BABS1201 Summer 2015-16 Manual
BABS1201 Summer 2015-16 Manual
BABS1201 Summer 2015-16 Manual
Student Name:
Student Number:
Tutor:
CONTENTS
Welcome
Course Outline
11
Course Structure
12
Graduate Attributes
13
Lecture Program
14
Administrative Matters
20
21
22
Student Declaration
23
24
38
54
Practical 3: Cell Structure 3 - Differences between plant cells & animal cells
- Differences between bacteria & eukaryotes
62
78
93
108
118
132
152
Course Convenors
BABS1201
Course Name
Academic Unit
Level of
Course
Units of Credit
Hours per
Week
variable
Number of
Weeks
8 weeks
Course
Convenor
John Wilson
Room G27, Ground floor, Biological Sciences Building
(02) 9385 1748
E-mail: j.e.wilson@unsw.edu.au
Drop in any time during business hours
Administrative
Support
Course
Web Site
Course
Manual
Practical
Class
Requirements
Recommended
Textbook
Scientific
Literature
Essay
Due Date
Practical 1
Thu
3rd
Dec
2015
Mark
N/A
Practical 4
th
Thu 7 Jan
2016
5%
Session
Theory
Exam 2
Final Theory
Exam
Thu
17th
Dec
2015
10%
40%
10
Assessment
Enzymes
Project
Biological
Modelling
Due Date
Practical 2
Thu
10th
Dec
2015
Practical 6
Thu
21st
Jan
2016
Practical 8
Tue
2n
Feb
2016
Mark
3%
2%
10%
Continuous
&
Practical 8
nd
Tue 2 Feb
2016
10%
Practical 9
Thu
4th
Feb
2016
10%
11
Course Outline
The course, Molecules, Cells and Genes encompasses four major themes. These themes
are not presented in turn, but rather will be presented in an integrated fashion.
Theme 1:
Thinking
like a
scientist
Theme 2:
Cell biology
and cell
architecture
Theme 3:
Metabolism
Theme 4:
Genetics
This theme introduces the skills of scientific thinking, including how to decide
what is true or plausible, and how scientists communicate. It also exposes
you to cutting edge research being conducted at UNSW.
Lectures and practical classes on this theme are interspersed through the
session, enabling you:
This theme describes the principal types of living cells, the key components
of cell structure, their functions, and how they relate to each other.
Lectures and practical classes on this theme should enable you:
To identify the different types of living cells, and the main similarities
and differences between them.
This theme outlines the key concepts of metabolism, the consumption and
generation of energy by living cells.
Lectures and practical classes on this theme should enable you:
differences
between
proteins,
This theme introduces the key concepts of modern genetics, including what
genes are, how they are regulated, how genetic information is transmitted
and how modern molecular biology can use genetics to understand biology.
Lectures and practical classes on this theme should enable you:
12
Course Structure
Practical
classes
Lectures
13
Science Graduate
Attributes
0 = no
focus
1=
minimal
2 = minor
3 = major
Activities / Assessment
Research, inquiry
and analytical
thinking abilities
Capability and
motivation for
intellectual
development
Communication
Teamwork,
collaborative and
management skills
Information literacy
Teaching strategies
14
Lecture Program
Please note that the lecture topics and learning outcomes listed below are a guide
only. Individual lecturers may provide you with updated topics & learning outcomes.
What is
BABS1201?
Scientific literature
Cells 1
Cells 2
Lecture topics
Course introduction.
Use of course resources: lectures, web site, and practicals.
Assessments.
Plagiarism.
Lecture topics
Communication between scientists: literature, presentations,
conferences.
Nature of peer review.
Primary literature and review articles.
Electronic databases.
Citations.
Learning outcomes
To be able to identify scholarly reports and to recognise the
principles behind the style and content of scientific journals.
To understand how scientific arguments are built by
reference to published scientific reports.
To appreciate the importance of verification in the scientific
process.
Lecture topics
What is life?
Bacteria, archaea and eukaryotes.
Principal differences between bacteria and eukaryotic cells.
Evolutionary relationships between cell types.
Learning outcomes
To understand the characteristics of life.
To be able to identify the fundamental differences between
bacteria and eukaryotic cells.
To comprehend that prokaryotes gave rise to single-celled
organisms with a DNA-containing nucleus the eukaryotes.
To understand the likely evolutionary relationships between
the different domains of life.
Lecture topics
Eukaryote organelle structure and function.
Bacterial cell structure.
The cytoskeleton.
Learning outcomes
To identify characteristic structures of eukaryotic and
bacterial cells and to describe their basic functions.
To describe the concept of endosymbiosis.
To list the main components of the cytoskeleton and briefly
describe their roles in the cell.
15
Macromolecules
Lecture topics
The four main organic components of cells nucleic acids,
proteins, lipids, carbohydrates.
Identification of important similarities & differences in
macromolecular structure.
Introductory concepts of breakdown and synthesis.
Functions of macromolecules structural, food storage,
enzymes.
Learning outcomes
To identify characteristic structures of protein, carbohydrate
and lipid molecules.
To describe the principal elements of their formation from and
breakdown to their molecular subunits.
To identify the importance of these molecules in cell structure
and in nutrition.
Cell Integrity
Lecture topics
Membrane structure.
The fluid mosaic model.
The roles of lipids and proteins in maintaining cell integrity.
Membrane permeability, diffusion and osmosis.
Learning outcomes
To comprehend the structure of the cell membranes and their
function in maintaining cell integrity.
To describe the different components of the cell menbrane
that play an important role in maintaining cell integrity.
To explain the non-selective diffusion of some small
molecules across cell membranes and osmosis.
Cellular transport
Lecture topics
Transporter proteins.
Passive and active transport.
Ion transport and membrane potential.
Vesicular transport.
Learning outcomes
To explain the mechanisms by which small molecules may be
selectively transported into and out of cells.
To comprehend the concept of a membrane potential arising
from ionic imbalances across cell membranes.
To describe the different types of endocytosis.
16
From gene to
function
Lecture topics
What is the genetic information?
An introduction to nucleic acid structure.
Bases as code.
Learning outcomes
Describe the basic structure of nucleic acids.
Explain how genetic information is encoded in nucleic acids.
Identify the differences between DNA & RNA.
DNA replication
Lecture topics
Mechanisms of DNA synthesis in bacteria and eukaryotes.
Learning outcomes
Explain the semi-conservative model of DNA replication.
Describe the basic steps involved in the process of DNA
replication.
Describe the function of the major enzymes involved in DNA
replication.
Lecture topics
Nature of genes and chromosomes.
Cell division: mitosis and meiosis.
Learning outcomes
To explain the difference between a gene and a
chromosome.
To describe the processes of mitosis and meiosis, the
differences between them and their purpose.
Metabolism I:
Metabolic concepts
Lecture topics
Catabolism and anabolism.
The role of ATP in "energy" metabolism.
Nutritional and metabolic diversity.
Respiration and fermentation.
Metabolic control.
Learning outcomes
Explain the differences between anabolism and catbolism.
Describde the process of cells breaking down molecules to
release chemical energy, render them harmless or allow for
recycling.
Explain the basic model for enzyme catalysis.
Describe the structure and function of ATP.
Explain the four main nutritional modes utilised by organisms.
To comprehend the importance of oxygen and respiration in
higher animals and plants.
Explain the concept of metabolic control via feedback
inhibition.
17
Metabolism II:
Extracting energy
from food
Lecture topics
Overview of the catabolism of carbohydrate, fat and protein.
Overview of glycolysis, the TCA cycle and the respiratory
chain.
Chemiosmosis - the formation of ATP by oxidative
phosphorylation.
ATP yields from glucose catabolism.
Learning outcomes
Describe the convergent catabolism of different
macromolecules.
Describe the central features of glycolysis, the TCA cycle and
oxidative phosphorylation.
To comprehend the basic principles of chemiosmosis - the
generation of a proton gradient by, for example, the
respiratory chain and the utilisation of the gradient by ATP
synthase.
To explain the advantages of respiration over fermentation
with respect to energy yields.
Photosynthesis:
Synthesising food
from energy
Lecture topics
Overview of photosynthesis.
Light harvesting.
The light reactions of photosynthesis.
The Calvin cycle.
Learning outcomes
To comprehend the functions of the different stages in
photosynthesis - light harvesting, the conversion of light
energy into chemical energy and carbon dioxide fixation.
To comprehend the overall organisation of the light reactions
in photosystems I and II.
To describe, in overview, the fixation of carbon dioxide and
synthesis of glucose in the Calvin cycle.
To compare and contrast the generation of energy from
photosynthesis or oxidation.
Metabolism in
review
Gene expression I:
Transcription
Lecture topics
Overview and revision of Metabolism I, Metabolism II and
Photosynthesis lectures.
Lecture topics
DNARNAprotein.
The genetic code.
Transcription: The synthesis of RNA from a DNA template.
Differences in gene expression between bacteria &
eukaryotes.
Learning outcomes
Describe the genetic code.
Explain how the instructions contained within DNA are
transcribed into RNA.
Define the three stages of transcription.
State the main differences in gene expression between
bacteria and eukaryotes.
18
Lecture topics
Overview: the translation of mRNA into amino acids.
Transfer RNA and its role in translation.
The ribosome as the protein synthesis factory.
The three stages of translation.
Control of gene expression.
Learning outcomes
Explain the processes of transcription and translation and
relate them to cell function and the role of ribosomes.
Describe the basic structure and function of tRNA.
Describe the three main stages of translation.
Explain the main differences between control of gene
expression in bacteria and eukaryotes.
The polymerase
chain reaction
Lecture topics
Polymerase chain reaction (PCR).
Learning outcomes
To describe the PCR technique and the basic steps involved.
To list several applications of the PCR.
Mutation
Lecture topics
Errors in reproduction.
Environmental influences (radiation, chemicals, viruses).
Beneficial mutations and natural selection.
Loss of function or changed function.
Gene duplication.
Relationship to selected disease.
Mutations in the immune system.
Learning outcomes
To explain at mechanisms by which mutations can arise.
Relate the occurrence of mutations to the outcomes for cells
and whole organisms.
To appreciate the importance of the rate of mutation for the
evolution of species.
Mendels laws of
heredity
Lecture topics
Mendels laws.
Essential concepts in genetics: allele vs. locus, genotype vs.
phenotype, homozygosity vs. heterozygosity, recessive vs.
dominant
Learning outcomes
To describe Mendels laws.
To explain the basis of inherited characteristics.
To explain why genotype does not always equal phenotype.
19
Mechanisms of
inheritance
Lecture topics
Modes of inheritance (single-locus, Mendelian traits).
Inheritance of complex traits.
Vertical inheritance vs. horizontal gene transfer.
Learning outcomes
To understand the varied modes of inheritance in different
organisms.
Population
genetics
Lecture topics
Hardy-Weinberg law.
Evolutionary forces that change allele and genotype
proportions.
Learning outcomes
To explain the evolutionary forces that influence population
genetics using the Hardy-Weinberg model.
Course review
Overview of BABS1201.
Exam structure and tips.
Student questions.
20
Administrative Matters
Expectations
of Students
Assignment
Submissions
Equity and
Diversity
Student Complaint
Procedure
Louise Lutze-Mann
l.lutze-mann@unsw.edu.au
Tel: 9385 2024
Science
Faculty Contact
21
Students who believe that their performance, either during the session or
in the end of session exams, may have been affected by illness or other
circumstances may apply for special consideration. For BABS1201,
applications can be made for in-session assessments tasks and the final
examination.
Students must make a formal application for Special Consideration for
the course/s affected as soon as practicable after the problem occurs and
within three working days of the assessment to which it refers.
Students should consult the A-Z section of the Student Guide 2014,
particularly the section on Special Consideration, for further information
about general rules covering examinations, assessment, special
consideration and other related matters. This is information is published
free in your UNSW Student Diary and is also available on the web at:
my.unsw.edu.au/student/atoz/SpecialConsideration.html.
How to apply
for special
consideration
22
23
STUDENT DECLARATION
I declare that this assessment item (Molecules, Cells & Genes Laboratory
Manual) is my own work, except where acknowledged, and has not been
submitted for academic credit elsewhere, and acknowledge that the assessor of
this item may, for the purpose of assessing this item:
o Reproduce this assessment item and provide a copy to another member of the
University; and/or,
o Communicate a copy of this assessment item to a plagiarism checking service
(which may then retain a copy of the assessment item on its database for the
purpose of future plagiarism checking).
I certify that I have read and understood the University Rules regarding Student
Academic Misconduct.
Signature: ...
Date: ...........
24
COURSE INTRODUCTION
&
LABORATORY SAFETY
CONTENTS
1.
2.
3.
4.
5.
6.
1.
Students should proceed to the appropriate laboratory (BioScience labs G20 and
G21) where practical class groups will be organised.
2.
INTRODUCTION TO COURSE
Your demonstrator will outline the scope of the course and explain the method of
continual assessment to you and answer any questions you have about them.
Assessment:
q Safety Quiz (compulsory)
q Essay (5%)
q Enzyme project (15%)
q Biological system project (20%)
q Session theory test 1 (10%)
q Session theory test 2 (10%)
q Final exam (40%)
25
3.
There are two major projects in BABS1201 which together will contribute 35%
towards your final grade. Both projects involve group work, which is best described
as cooperative learning.
Cooperative learning is a teaching method in which students work in small groups to
accomplish a common learning goal under the guidance of a mentor.
Positive features of cooperative learning are:
Students positively depend on each other in a team to achieve a mutual
learning goal.
Students engage in face-to-face interactions.
Students are assessed individually and held accountable for equally sharing
and contributing to the mastery of learning goals (peer reviewing)
Students use and develop appropriate collaborative and interpersonal skills to
teach and encourage each other to learn.
Cooperative learning improves students thinking and helps them construct their own
understanding of science content by strengthening and extending their knowledge of
the topic. The sharing of ideas allows students to explore, refine, and question new
ideas (Chi et al. 1994; Chin and Brown 2000; Jones and Carter 1998; Wood 1992).
Cooperative learning promotes student involvement and engagement. Students must
take responsibility for their own learning and not depend solely on the teacher. The
use of cooperative learning supports this outcome and provides all students with
public opportunities to make their thoughts visible to others by allowing them to talk
about and consider their own as ideas as well as those of others (Chin and Brown 2000;
Jones and Carter 1998; Kagan 1994; Wood 1992).
Enzymes project
This task is a course assessment component and is
worth 15% of your final mark in BABS1201. In order
to complete this task, you will be assigned to a
team of two (2) students within your demonstrator
group.
You will design and implement an experimental
protocol that investigates one or two factors that
affect enzyme activity This project will require your
participation over several weeks of the session.
26
Outline:
To perform background research on enzyme structure and function and design and
implement an experimental protocol to explore the activity of one of the following
enzymes:
o Amylase
o Catalase
o Bromelain
o Rennin
Background:
Enzyme activity is influenced by factors such as concentration of the enzyme,
concentration of the substrate, pH and temperature. All enzymes are affected in
specific ways by these factors. Thus, there are optimal catalytic conditions for each
enzyme. Since enzymes are found in living organisms, the optimal pH and
temperature reflect the environmental conditions in which these organisms function.
For example, in mammals the pH of cell cytoplasm is approximately 7, but the pH of
the stomach cavity can be as low as 2-3. Therefore, enzymes that function within
mammalian cells typically have a neutral pH optimum, whereas the stomach enzyme
pepsin works best at an acidic pH. Similarly, the optimal temperature for an enzyme
reflects the temperature of its natural environment (~37C in the case of human
enzymes).
Learning outcomes:
Assessment:
There are three assessable components to this project. Depending upon the item, the
grading may be as a team (pair) or individual.
o Experimental design (3%) (group submission)
o Experimental notes (2%) (group submission)
o Final report (10%) (individual submission)
27
Timeline:
When
Introduction
day
In your own
time
Practical 4
Practical 5
Practical 6
Practical 8
Component
Description
Discussion on
experimental
design
Design of
experimental
protocol
Discussion &
review of
experimental
protocol
During your lab discussion this week, you will submit your
final draft experimental protocol to your demonstrator for
review. Your teams protocol must include the aims and
purpose of the experiment, a complete list of the materials
and equipment required, a detailed description of the
experimental methods/procedures to be employed and the
expected outcomes of the experiment. Your demonstrator
will give you feedback relating to the feasibility of your
protocol, along with any suggestions for improvement.
Submission of
experimental
protocol
Enzymes
practical
Report
submission
28
29
Resources:
Below, you will find a list of equipment, reagents and solutions that our technical staff
will be able to provide upon your groups request. You should aim to design your
experiment based on this list. Please note, however, that the quantity of each item or
solution may be limited in some cases.
Equipment available:
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
o
Test tubes
Beakers
Measuring cylinders
Glass stirring rods
Mortar and pestle
Watch glasses
Volumetric flasks
Thermometers
Timers
Scalpels
Test tube racks
Water baths
Stop watches
Rubber bands
Metal spoons
Petri dishes
Balance
Razor blades
Universal indicator
HCl (0.1 2.0%)
NaCl
3% hydrogen peroxide solution
Amylase
1M NaOH
Buffer solutions
Benedicts solution
Cheese cloth
Hot water baths (35C, 45C, 50C, 60 and 90-100C)
Ice
30
3b.
Learning outcomes:
Assessment:
The project is based on the design and construction of a biological system. The
topics may vary widely in scope and difficulty, and the project assessment will take
this into account.
The following aspects of the project are assessable:
The effort made by the individual student
The collaborative effort of the team (evidenced by group diary notes)
The quality and resourcefulness of the model developed
The completeness and scientific validity of the model in relation to the
system addressed
There are two assessable components to this project.
o Diary (10%)
o Model (10%)
31
Timeline:
When
Component
Description
General
discussion
Practical 2
Tutor review
During your lab discussion this week, you will discuss your
biological system with your tutor for review. Your tutor will
give you feedback on the appropriateness and feasibility of
system, along with any suggestions for improvement.
In your own
time
Research &
design of
system & model
During this time you will research and diarise all aspects
your biological system and commence/consider the design
of your proposed model.
Tutor review
During your lab discussion this week, you will discuss your
model with your tutor for review. Your tutor will give you
feedback along with any suggestions for improvement.
Preliminary grade for your diary.
Practical 8
Tutor review
Your model
should be near completed. During lab
discussion time, you should show evidence of your design
and with your tutor for review.
Submission of diary to your tutor for final grading.
Practical 9
Science fair
Practical 1
In your own
time
Practical 5
32
4.
This week you will meet your laboratory demonstrator, and be introduced to the basic
principles of laboratory safety. This is a requirement of the Occupational Health and
Safety legislation. At the end of the class, you will be required to sign a declaration
that states that you have read and understood the rules. If you fail to do this, you will
not be permitted to participate in further practical classes.
General conduct:
A laboratory is intended for serious work and rowdy behaviour is forbidden.
Students must read the instructions to their experiments carefully before starting
work, and should be aware of all possible hazards.
No undergraduate students are to work in the laboratories outside class hours
without permission and some degree of supervision.
All accidents and injuries must be reported to the lecturer or demonstrator in charge
of the practical class, so that treatment may be provided if necessary.
Evacuation:
If there is a fire or other major calamity an alarm will sound. Messages may be
broadcast from the universitys Emergency Response group. Unless there is an
immediate danger nearby, when you first hear the initial Prepare to Evacuate alarm,
stop what you are doing and wait for further instructions.
Follow the instructions from your lecturer or demonstrator. Close all the doors and
windows if possible. Quickly check to see that everyone is out of the room. Move
steadily to the exit. If for some reason, you are not in the groundfloor labs, move
quickly to the nearest stair well and out of the building. Do not use the lifts. Assemble
in the Michael Birt Gardens in front of the Chancellery Building (near Gate 9 on High
Street). Supervisors should bring the class roll and check that every one has left the
building.
Risk assessment:
Working in a laboratory is inevitably associated with certain risks. Good laboratory
practice means working in such a way as to eliminate, or at least minimise, these
hazards. In order to perform your work safely and to comply with government
legislation's, a risk assessment has been conducted on all of work that will be
performed in this subject in the laboratory and the following potential risks have been
identified:
Biological hazards: All microorganisms are potentially harmful if ingested or
exposed to body surfaces. Some organisms used in this class may be opportunistic
human pathogens, however none are considered to pose a significant risk if handled
appropriately (see procedures below).
33
Chemical hazards: Most of the chemicals used in this subject (eg. in solid and liquid
media and most buffers) are not hazardous at the concentrations that are being used,
however all chemicals should be considered potentially harmful. Some practicals
employ hazardous chemicals. In these cases the hazard is described in the class
directions for that specific exercise. The concentration of antibiotics in media are
generally not harmful, however contact with skin should be avoided.
Note: Material Safety Data Sheets (MSDS) are available for all of the hazardous
chemicals from your tutor. You should be familiar with the relevant MSDSs prior to
commencing your practical work.
Physical hazards: Bunsen burners and heat from other sources such as water
baths, breakable glassware, sharp objects such as plastic tips and needles.
Hazards involving work environments: The combination of large numbers of
students performing laboratory work (eg. with Bunsen burners alight), and the
necessity to wear protective clothing (see below), especially in summer weather, may
cause discomfort to some students. In addition, the nature of laboratory design
(benches and stools) may cause discomfort to some students.
Procedures for reducing risks:
In addition to the general risks that have been identified with laboratory work for this
subject (see above), any additional risks associated with specific practicals are
written in this manual at the beginning of each practical description. At the
commencement of each new practical your tutor will review the risks with you. At the
commencement of each class the procedures may also be reviewed. You may be
examined on your understanding. It is imperative that you be present at the
beginning of each class to ensure that you are available to review safety procedures.
If you are not present you may be excluded from the class. Below are some simple
rules that you must follow which will ensure good laboratory practice and minimise
the consequences of risks:
Wear adequate protective clothing. This will protect you from contamination by
cultures and chemicals as well as protecting the cultures and chemicals from
contamination by you. A laboratory coat must always be worn while in the lab, and
removed on leaving. Where necessary (as advised by your tutor), protective gloves
should also be worn. These will be provided and must be disposed of in the
designated Scientific Waste bins. Do not wear lab coats or gloves outside the
laboratory! Adequate protective clothing also includes footwear. Fully enclosed shoes
must be worn while thongs and other open, loose footwear are not permitted. Safety
glasses will be provided if required.
You must not eat, drink, smoke, apply make-up etc in the lab. Neither should you
bring food, drink etc. into the lab. Never leave food or drink on laboratory benches!
Habits such as chewing the ends of pens and pencils, nail biting etc. are often difficult
to avoid, but you should make a conscious effort not to do them. Do not sit on
laboratory benches. All bags and/or extraneous clothing items must be stored under
benches and not on benches or on the floor between the benches where they could
act as a tripping hazard.
34
Do not invite anyone into the lab. They may not be aware of the hazards and may
themselves create additional hazards.
Keep everything covered. Do not leave the plugs off flasks or caps off tubes and
bottles. As well as minimising spillages, this will prevent contamination of cultures
and solutions.
If there is an accident with a microbial culture, or hazardous chemical, ask a fellow
student to call someone in authority immediately. Do not move and risk the spread of
contamination. If there is a fire, remove yourself from immediate danger and call
someone in authority immediately. If there is a small spill of a non-toxic or harmless
chemical or solution such as water, you should clean it up yourself or check with your
demonstrator first for the best way to proceed.
Before leaving the laboratory tidy your bench, clean your bench area and
alwayswash your hands.
If you feel discomfort from your work (eg. heat exhaustion or back pain), consult
your tutor or the course authority.
If you get any biological or chemical substance (eg. sodium hydroxide) in your eye,
ensure that you immediately go to a tap and wash your eye. While washing your eye,
alert someone to your situation so that they can assist you and gain the attention of
someone in authority. Continue to wash your eye until someone in authority indicates
for you to do otherwise. It is imperative that you take this seriously as you may risk
permanent eye damage if it is a harmful chemical. Note: you should always wear
safety glasses when handling hazardous substances. These will be provided if
required.
Acid splashes on the skin should be immediately washed thoroughly, and in the case
of a major spill, you should douse yourself immediately using the safety showers.
You should ensure that your demonstrator is aware of what has happened, and they
may refer you to a school safety officer or medical officer.
You must sign the declaration below and have it witnessed by a tutor or demonstrator before
you will be permitted to take part in practical classes.
I, ..............................
name
.......................
student ID
certify that I have read and understood the Safety in Laboratories information above, and
agree to abide by these rules at all times when in University Laboratories.
Witness: ..................................
name
........................................................
position
35
5.
In order to be permitted to take part in laboratory classes, you must also complete an
online Laboratory Safety Quiz that is accessed through the BABS1201 Moodle site.
Prior to your first laboratory class, go to the BABS1201 Moodle site and enter the
Laboratory Safety Quiz module by clicking on the appropriate icon on the home
page. Follow the instructions provided there and use the above information on
occupational health and safety that you have discussed with your demonstrator today
to complete the quiz. When you have finished the quiz and submitted all your
answers, you will receive a mark out of 12. If any of your answers were incorrect,
then you must attempt the quiz again and keep repeating this proceess until you
have scored a mark of 12/12 (that is, 100%). Since it is crucial that you are aware of
all important health and safety rules and regulations, you can attempt the quiz as
many times as required for you to get all the answers correct. Your final quiz mark
will be checked prior to your first lab. If you have not scored 100% in the quiz by 9am
on the day of your first practical class you will not be permitted to attend that lab class
or any subsequent lab class until you have satisfied this requirement.
6.
Introduction:
Today you will start your training in how to think scientifically, and to evaluate
whether information you come across is good value and reliable, or is merely
someones opinion. This is a skill which will be important when you prepare
assignments in this course. The exercises today are meant to make you think about
how you evaluate information every day of your life, and how skills in the evaluation
of information can be applied to the study of science and of scientific discovery.
Activity 1:
Divide into groups of 4-5. Your tutor will allocate one of the items in the list below to
each group. You all make decisions about purchasing these types of things.To do
this, you look at and evaluate a number of sources of information in order.
o Mobile phone
o Car
o Computer
o iPad
In your groups, discuss purchasing one of these items, and analyse the processes
you go through when doing so. Answer the following questions:
36
If you find two sources of information that are conflicting, how do you decide
which one to believe?
Activity 2:
Form groups of 4-5 students.
As a group, work out the dimensions of the UNSW sign on top of the library building.
Please note: Do not take any risks such as climbing the building!
37
SECTION 1:
PRACTICALS 1- 3
EXPLORING CELL STRUCTURE
This sequence of three practical classes explores aspects of cell structure and
concepts that will be discussed in lectures. You will learn some of the techniques we
use to explore cells.
The goals for this sequence are:
To become proficient at identifying and reporting on microscopic structures
observed through a light microscope.
To be able to identify an unknown cell type and report on your findings to your
colleagues, including:
- What type of cell (bacteria, eukaryote, plant or animal) you have.
- What procedures you used to identify your cells.
- What characteristics of those cells enabled you to identify them:
Organelles?
Size?
Other features or structures?
To be able to record observations and results from your investigations in the
manner of a scientist, including appropriate referencing of the scientific
literature.
Graduate attributes:
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PRACTICAL 1
CELL STRUCTURE I
PRINCIPLES OF MICROSCOPY
CONTENTS
1.
2.
3.
4.
5.
Discussion of essay
Principles of light microscopy
Setting-up the light microscope
Observing microscopic life
Reporting on your findings
1.
This assignment must be completed and handed in at the commencement of your lab
in Practical 4.
This assignment is designed as a first university writing assignment. It will be
followed by other assignments in this course, and in other courses, that will
progressively introduce you to the demands of scientific report writing. This report,
however, is not an exercise in scientific report writing. It is a more personal piece of
writing, which in part reflects upon your own experience locating and reading a
scientific article. A major objective of this task is to see if you can write clearly and
concisely. It is not an objective to focus on the scientific content of the research
article. If, as a result of this assessment, we think you have problems writing, we will
refer you to the Learning Centre for assistance.
The essay should be about 500 - 600 words long. You must perform a word count
and print the count on the coversheet that you attach to your essay.
Your essay will describe a peer-reviewed journal article that you identify from the
primary literature.
The article may come from any science discipline. You must attach a copy of the
journal article to your essay, when you submit the hard-copy.
Your essay must contain the following:
o A simple introduction that describes the purpose of your report.
o A description of the discipline that you think best describes the research that is
reported in the article. For example is it zoology, or microbiology, genetics or
something else that you think best describes the work. Remember that there
may be more than one discipline name that you can think of, and you could
discuss the different possibilities if that is the case. You should say a little bit
about what you think the discipline is about. Of course you do not have space
to do this in any detail. In some cases it may be easy. In others, the
boundaries of the discipline may be unclear to you. Feel free to discuss your
uncertainties as this is a reflective essay.
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o A description of the journal. Tell your reader as much as you can, in the
available space, about the journal. Write about the relationship between the
journal you have chosen and the discipline. In some cases, this will mean you
will find out a little about a professional society that is associated with the
journal. The journal may be a general one, that serves many disciplines, or
may be a journal that is strongly associated with a particular scientific subdiscipline. The journal may target regional, national or international audiences.
This is something to write about.
o A description of the purpose of the study, and the results of the investigations
that are reported. Dont get bogged down with the detail. You have very little
space to do this, so you must focus on the main points. You may not
understand very much. You may not understand anything at all. If this is the
case, do not panic! You will not be penalised as long as you can sensibly write
about your lack of understanding. (Remember this is a reflective essay, where
you are free to discuss both your triumphs and difficulties!)
This part of your essay could look something like this:
Although this article was chosen because its title seemed
understandable, and suggested that the paper was about the diet of
bandicoots, it proved impossible for me to understand it at all. The first
sentence alone included 15 words that I had never seen before.
Although I used a dictionary to clarify the meaning of most of the words,
I was still unable to make any sense of the article. etc etc
The assignment must be professionally presented. You cannot write in pencil or pen,
but must use a word processor. Organise the document neatly, and try to make it
easy for your demonstrator to read. Avoid spelling errors. UseSpell Checker!
Marks will be deducted for late submission, unless the delay is due to medical or
other serious reasons that can be professionally documented. If you wish to ask for
such special consideration, you must provide your demonstrator with a Medical
Certificate or other professional documentary evidence to support your claim.
Your essay will be marked by your demonstrator, and for reasons of equity, the
results will be reviewed by the course convenors to ensure that the marks are
appropriate between groups. You will not be given your marks back until all
assignments have been submitted and marked.
You will be rewarded for carefully following all the above instructions, and you will
lose marks for each omission or error. Remember that you can score full marks
without understanding the article, if you just follow the instructions.
Note that this is not a scholarly essay, and that therefore we do not expect you to
provide citations. You simply report on the one paper, as described above. As this is
a reflective essay, we expect that you will use the first person in your essay. That is,
you may write I did this, and I did that.
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2.
Light microscopes are a powerful tool for identifying and examining single cells or
tissues. While there are many other techniques that can be used in conjunction with
light microscopy, such as electron microscopy, DNA fingerprinting and biochemical
techniques, light microscopes are still a crucial element of our scientific armoury, and
are widely used.
For example:
Hospital laboratories will look down a microscope to help identify a bacterial
species, such as meningococcus, that is causing illness.
Pathology laboratories will look at blood cells down a microscope to identify
leukaemias, or tissue samples to identify other cancers.
Ecologists may look down a microscope to identify the microscopic organisms
present in the environment that can indicate the presence of pollution.
Botanists use microscopes to identify seeds that are fertile.
Biotechnologists may look down a microscope to identify cells that have
successfully been engineered to express a desired protein.
The characteristics of individual organisms that can help identify them include size,
shape, and internal structures. You can also use chemical stains to colour the
organisms which can provide even more information. So knowing how to get the
most out of your light microscope is a skill that you could need at many stages of
your future career.
The compound light microscope:
The compound light microscope is a precision optical instrument designed for
producing magnified images of objects using two or more glass lenses. The term
light refers to the fact that light transmits the image to your eye, in contrast to
electron microscopes in which beams of electrons are used to create magnified
images. Compound deals with the microscope having more than one lens.
Microscope is a word created from "micro" meaning small and "scope" meaning
view.
The key factor in optimising the compound light microscopes performance is not
magnification, but resolution. Resolution is the ability to separate two closely spaced
items. A lens magnifies by bending light. Optical microscopes are restricted in their
ability to resolve features by a phenomenon called diffraction which, based on the
nature of the optical system and the wavelengths of light used, sets a definite limit to
the optical resolution. Due to the diffraction of light, even the best optical microscope
is limited to a resolution of 0.2 micrometers. In other words, the smallest detail that
can be seen under the highest magnification of the light microscope is 0.2
micrometers (m).
When using the 100X lens the light is bent at such an angle as it passes from glass
into air that it is impossible to properly or clearly observe the specimen. To prevent
the light being bent away on an angled path from the objective lens, immersion oil is
used. Immersion oil has the same refractive index as the glass, so light travelling up
through the slide, the oil and then the objective lens, is not refracted again until it
passes from the convex upper surface of the lens into the air above.
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That bending, however, is what the lens is designed to do, sending the rays which left
the specimen at angles up the tube at new angles, to be resolved and magnified by
the ocular lens.
The oil immersion lens (100X), when used with a drop of oil, prevents this refraction
or deflection of angled light from its straight path as would occur if the light were to
pass at an angle from glass into air.
To use the oil immersion lens (100X), a drop of immersion oil is placed on the
specimen and the oil immersion objective (100X) is then lowered into the oil.
Please note that immersion oil must not be used with any other lens (4X, 10X, 40X),
as these lenses are not designed to come into contact with immersion oil, and the
use of oil will result in damage to the lens.
Parts of the light microscope:
There are many makes and models of light microscope. However, all light
microscopes are fundamentally the same, have similar controls and functions. The
microscope illustrated below is typical of the light microscope used in UNSW
teaching.
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1. Switching on microscope
Turn the power switch on (1).
Move the voltage control slide (2) to
set the light intensity.You should not
need to set the intensity to the
maximum power.
2. Specimen placement
Open the spring-loaded finger of
the specimen holder (1) and insert
the slide that is provided for each
student.
3. Focus
Swing in the 4x objective (1).
Using the coarse adjustment (2), raise
the stage as high as possible. Bring the
specimen into focus by lowering the
stage, using first the coarse and then
the fine adjustment knobs.
Swing in the 10x objective and refocus
using the coarse and/or fine adjustment
knobs.
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4. Interpupillary distance
Looking through both eyepieces,
move the knurled dovetail slides until
a suitable binocular image is obtained.
5. Diopter adjustment
To achieve maximum binocular clarity, an
adjustment can be made to compensate
for differences in the vision of your left and
right eyes. Look at the image through the
right eyepiece with your right eye, and
focus on the specimen with the fine focus
adjustment.
Looking at the image through the left
eyepiece with your left eye, rotate the
diopter adjustment ring (1) to focus on the
specimen without using the focus
adjustment knobs.
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As light strikes the specimen the qualities of the light are changed in several ways
that give the visual image we perceive. It may be scattered or reflected away from
a path leading to the objective, darkening the image; it may be completely occluded
by solid structures that appear black to the observer; specific wavelengths of the
light may be partially absorbed by certain substances (including stains), giving a
characteristic colour to structures containing them.
Microscopy trouble shooting
Apparent fault
Field dark
Colour of objects
indistinct
Poor resolution
Unable to focus on
object
Possible cause
Power (lamp) not on or
turned down too low
Condenser diaphragm
closed
Lamp filament burnt out
Condenser diaphragm
closed too far
Condenser either too far
open or too far closed
Cover-slip too thick
Slide up-side down
Focusing attempts too
rapid
Objective has insufficient
resolving power
Objective covered with
dried immersion oil from
previous use
Dirt on eye lens of ocular
Dirt on condenser lens
Dirt on filter
Air and/or water bubbles in
immersion oil
No oil contact between oil
immersion objective and
slide
Correction
Turn power on & check
voltage
Open diaphragm
Replace lamp
Open diaphragm
Adjust condenser
diaphragm
Replace
Invert slide
Use fine focus and adjust
more slowly
Use higher power
Clean with lens tissue and
solvent
Clean with lens tissue
Remove oil with lens
tissue. Re-apply
Adjust with course /fine
focus control
Calculating the total magnification of an image that you are viewing through the
microscope is really quite simple. To get the total magnification, take the power of the
objective (4X, 10X, 40X) and multiply by the power of the eyepiece to give total
magnification.
If you are looking at something through the 40X objective, what is the actual
magnification of the object you see?
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field number
objective magnification
18
10
1.8mm
Therefore an object on the slide which occupies half the field of view will measure
approximately 0.9mm or 1mm across.
Accurate measurements using the eyepiece scale
In order to provide an accurate scale for a drawing it may be necessary to have
accurate measurements. A ruler or micrometer is built into the eyepiece of your
microscope. A microdot slide of the number 5 has been provided as a trial slide.
With this slide on the stage and in focus, observe the eyepiece micrometer. Notice
that the scale has 100 divisions.
Starting with the lowest power, move through the different non-oil objectives and note
that the size of the ruler does not change. However the apparent size of the 5
changes with each new objective lens used. Therefore the divisions of the ruler
include a different amount of the 5 with each different objective.
The high quality of your microscope lenses is such that calibration made at the
factory are good for all microscopes of the same model.
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You can get an accurate measurement of any object on a slide at any magnification.
Test this by measuring the 5 on the microdot slide.
Using the scale, how high and how wide is the 5 ?
Now you know the size of the object seen through your microscope. However
someone looking at a drawing you made of it will have absolutely no idea of its actual
size unless you also include some indication of size. This is done by placing a scale
on the drawing.
4.
Experimental procedure:
Obtain a small sample of the pond water provided.
Place a drop on a clean microscope slide, and gently lower a coverslip onto the slide
as shown in Figure 1 below. This provides some protection for your specimen. It
prevents the specimen drying out, and it allows you to place oil on top of the coverslip
when you wish to use the oil immersion lens Be careful not to squash your specimen.
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Can you tell whether they are plants or animals? What characteristics might
help you decide?
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5.
One good way to report to others what you see down a microscope, is to draw what
you see. You do not need to be artistic, just accurate and clear.
Make sure you recognise and label important characteristics of the cells you see.
This record might help you identify unknown cell types in later weeks (e.g. organelles,
membranes, size, etc.)
Guidelines for drawing:
Drawing remains an important method of recording biological observations. It is also
a useful thing to do since it encourages the observer to look more carefully at the
specimen. For this reason, learning to produce good accurate drawings of your
material is an important part of practical work.
Outline drawings:
these drawings show relationships between parts of the subject, but provide little
detail. When using a microscope, line drawings are usually made to record what is
seen with the low power objective lens.
See Figure 2 below.
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Where specimens have repetition of detail it is best to make an outline sketch of the
whole specimen or field of view and then illustrate a clearly defined part of this sketch
with a separate detailed drawing as illustrated in figures 2 and 3.
Label the drawings and diagrams fully in pencil. Keep your labels horizontal and to
the side of the drawing, and rule lines to the appropriate parts. Do not use
arrowheads. Provide a title for each drawing. If notes are necessary as part of your
observations, place them at the bottom of the drawing or near the appropriate label.
This allows a combined record of structural and functional observations. There
should be a scale with each drawing to indicate size.
Your observations:
Make line drawings as figures 4 and 5, and work out the actual size of any two of the
organisms you see down your microscope.
Figure 4:
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Figure 5:
Re-adjusting your microscope:
To help you remember how to adjust your microscope, a second short video will be
played.
On completion of microscopic examination:
When finished with your microscope, before returning it to the cupboard, always:
o If appropriate, clean oil from the oil immersion lens and from other lenses too if
they have been contaminated with the oil
o Return the light intensity to the lowest setting and then switch off.
o Rotate the nosepiece back to the 4X position.
o Remove any slide from the stage.
o Dry any liquid from the stage.
o Secure the power cord.
N.B. You must clean your lenses using the lens tissue provided: Never use ordinary
Kleenex, as this can scratch lenses.
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PRACTICAL 2
CELL STRUCTURE II
IDENTIFYING DIFFERENT CELL TYPES
OBJECTIVES
o To identify key differences between eukaryote and bacterial cells, including
their size and structure.
o To identify intracellular structures of an example of a eukaryotic cell.
CONTENTS
1.
2.
3.
4.
1.
Introduction:
In this exercise, you will examine a water sample containing Spirogyra. Note that we
are not providing you with a pure culture. Samples were collected from local ponds
and so will contain a range of protists, plants and animals.
All living cells can be divided into three main types: bacteria, archaea and
eukaryotes. Bacteria and archaea are very similar in structure and wer once
collectively termed prokaryotes. Animals, plants and fungi are eukaryotes. There are
many differences between the cell types, but the most obvious is that bacteria and
archaea do not have a nucleus, whereas eukaryotes do. Also, as you are learning in
lectures, eukaryotes have internal structures called organelles. Other important
differences cannot be seen down a light microscope.
Spirogyra is a green algae (eukaryote), composed of cells arranged in long
unbranched filaments. Each cell contains one or more long, green ribbon-like
chloroplasts that wind around the periphery of the elongated cells.
As well as its distinctive ribbon-shaped chloroplast(s), Spirogyra has a cell wall, and a
large central vacuole, and at its centre it has a nucleus. The degree of coiling of the
chloroplast(s) seems to vary a great deal in different filaments, from being almost
straight and lying along the long axis of the cell to being tightly coiled.
The nucleus and pyrenoids (organelles in or extending from the chloroplast and
associated with reserve food accumulation) in the Spirogyra cell are normally
colourless. They can be stained with iodine to make them more visible but this kills
the cells.
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Focus on an individual cell with the 10X objective. Have a look at the general layout
of the cell. See if you can identify the cytoplasm around the edge of the cell, the large
central vacuole, the nucleus and the coiled ribbon-like chloroplast(s).
Make a line drawing of a chain of at least three Spirogyra cells, and put a scale on it
(figure 1). Provide a title for your figure. The aim of this drawing is to illustrate
accurately the overall shape of the organism, the shape of each cell and how the
cells are joined to one another. Do not show any structures within the cells.
N.B. Dont let your specimen dry out completely. If it looks as though it might be
drying, add another drop of pond water. You do not need to remove the cover-slip just add the drop carefully at the side.
Figure 1:
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In a cell where the chloroplast(s) are tightly coiled, work out the direction of coiling
(right-handed or left-handed helix) by varying your plane of focus. To do this it is
necessary to determine when you are in focus in the upper plane and when you are
in focus in the lower plane, and then focus through the top, middle and bottom of the
cell.
Record your findings by making simple diagrams (Figure 2) indicating the
appearance and position of a chloroplast ribbon at each of the three levels of focus in
the cell to illustrate the direction of coiling.
Figure 2:
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Figure 3:
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Figure 4:
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Assuming a Spirogyra cell is a regular cylinder and the width measurement is a true
diameter, calculate the average volume of the cell in the space below:
Using the 100X oil immersion objective, make similar measurements on the Bacillus
cells. (A word of caution: be sure that you are only measuring the length of one
bacterium, not a group or chain of bacteria). Using the same assumptions as for
Spirogyra, calculate the average cell volume below:
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4.
Introduction:
Mitochondria are not easily seen in living cells, but it is possible to increase their
visibility by staining them in a solution of pale yellow tetrazolium salt. This is a vital
stain which enters the cells and is reduced in the mitochondria to form an intense
coloured compound (purple or blue).
Safety note:
Tetrazolium salts are hazardous, so keep them off your skin. Disposable latex gloves
will provided for your use.
Procedure:
Note: This procedure needs to be done carefully, and includes a 1 hour incubation.
Make sure you set this up at the beginning of your class. While the cells are staining,
you can proceed with other tasks.
Place about 10 drops of the tetrazolium solution into the container provided on your
bench. Immediately cover the container with foil to protect it from light, as tetrazolium
salts are sensitive to light and rapidly decay.
Cut several thin slices of surface tissue from the terminal centimetre of the broad
bean root tip with a razor blade, and place them immediately into the solution in the
container. Cover the container again and allow 1 hour for the reaction to take place.
After one hour, mount a piece of tissue, using water and cover-slip, and examine the
thinnest part under the 10X and 40X and, if possible, the 100X oil immersion
objectives. It may help if you close down the condenser diaphragm to get higher
contrast. The mitochondria should appear as dark elongated or more or less round
structures, about the size of bacteria, throughout the cytoplasm.
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Figure 1:
Look at the electron micrographs of mitochondria available in the lab.
What structures can you see here that you cannot see under your microscope?
Why do you think you cant see such structures in the cells you stained?
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PRACTICAL 3
CELL STRUCTURE III
DIFFERENCES BETWEEN PLANT CELLS & ANIMAL CELLS
DIFFERENCES BETWEEN BACTERIA & EUKARYOTES
OBJECTIVES
Living cells come in a range of shapes, sizes and degrees of complexity. In this
practical you will perform a procedure commonly used to assist in the identification of
cells - chemical staining. Different types of stains react with different kinds of
molecules, and so cell structures may or may not stain with different coloured stains.
We can use this to identify cell structures and compartments. There are two general
ways of staining cells. They may be stained when they are alive (vital stains) or
when they are dead. Cells are often chemically fixed a technique that prevents
decay and preserves important features of the cells. You will use both types of stain
in this class. You will also remind yourself of the main differences between bacterial
cells and eukaryotic cells (plants, fungi and animals).
o To identify key differences between internal structures of prokaryotic and
eukaryotic cells
o To become competent with basic staining procedures and light microscopy of
different types of cells
o To identify and report on key internal structures of a range of cell types.
CONTENTS
1.
2.
3.
4.
5.
6.
7.
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1.
In this procedure you will be using a stain, toluidine blue, that stains the nucleolus
purple (indicating the presence of RNA) and the nucleus pale blue (DNA).
Procedure:
Lightly scrape the inside of your cheek with the wooden stick provided. This allows
you to collect some of the so-called epithelial cells that line many surfaces of the
body.
Mount the scrapings directly on a microscope slide, and add a drop of toluidine blue
solution. Leave 5 minutes for stain to work.
Cover with a coverslip and examine under 10X and 40X objectives.
Observe individual epithelial cells: what can you see?
Compare your cheek cells with the prepared slide of a corn root tip. In this
preparation, you will find many nuclei in various stages of division, but concentrate on
cells with nuclei that are not dividing, i.e. nuclei that have a clearly defined circular
outline and contain one or more nucleoli.
Can you see clear gaps between the cells in your corn root? What might this be?
Hint: what feature do plant cells have that animal cells dont?
What are the major differences between the plant cells and your cheek cells
(animal cells)? What are the common features?
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Draw 2 cells from both the cheek cell and the corn root preparations to show their
shape (Figure 2). Include their nucleus and any other internal structures that you can
see, making particular note of differences. Label your drawings and include a scale.
Figure 2:
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2.
Procedure:
You could not see details of the cell wall in your toluidine stained slides. Look at the
demonstration slide stained specifically to show the carbohydrate rich cell walls.
Plant cells often contain a central vacuole.
vacuoles in plant cells.
Can you see central vacuoles in your corn root slides? Explain why this might be
so.
With the forceps provided, carefully mount a young leaf of the water plant Egeria in
pond water, and examine with the 10X and 40X objectives.
Can you find chloroplasts?
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Figure 3:
Leave your Egeria cells for a few moments to recover from the shock of being
removed from the plant, and look at it again.
What differences can you see?
Record your observations, and make a simple drawing of the main features that you
see (Figure 4).
Figure 4:
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3.
There are other internal cell structures that are not visible down a light microscope.
Look at the electron micrographs that are available, and identify as many of the
features as you can. Record the structures that you recognise, and identify their
main function in Table 1.
Table 1:
Structure
Function
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4.
Because bacterial cells are generally smaller than eukaryotes, and have a less well
defined internal structure, it can be difficult to see them well under light microscopy,
unless you use the high power (100X) oil immersion lens. Today you will look at 2
different bacteria, and you will use several different stains.
Procedure:
Work in pairs and divide the work between you, but make sure you look at all slides.
Negative staining
Negative staining uses a stain that is excluded from the cells, so you have a dark
background with a light area highlighting each cell.
Mix a small drop of 4% nigrosine with a drop of Rhodospirillium suspension on a
clean microscope slide.
Using a clean cover slip, smear the suspension over the slide, and allow it to dry
completely under the lamp on the side bench.
Add one drop of immersion oil to the slide. This acts as a mounting medium,
allowing you to now to cover your specimen with a coverslip.
Look at your cells under 10X to focus, and then under 40X. When you have a clear
focus, add one drop of immersion oil on top of your coverslip, then examine the slide
under 100X. Make notes and/or drawings of what you see.
What shape are the bacterial cells?
Positive staining
Positive staining stains cells, leaving the background unstained. Toluidine blue is a
positive stain.
Put a drop of bacterial suspension on a slide, smear it as before, and allow it to dry
under the lamp.
Add one drop of toluidine blue solution on top of your smear, and leave it for 5
minutes on the bench.
Gently rinse the slide with distilled water, using the squeeze bottles provided. Be
careful not to squirt too hard, or you may wash the bacteria off your slide. Dry the
back of your slide with a tissue, then leave it under the lamp to dry completely.
When the slide is dry, place a drop of immersion oil on the smear as a mounting
medium, and cover with a coverslip.
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Focus the bacteria clearly under the 40X objective, then add a drop of immersion oil
on top of the coverslip, and examine under the 100X objective.
What features can you see?
Figure 5:
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5.
Using stains directly on cells can be useful, but often, much more detail is visible if
you fix your cells before staining. This is because fixing tends to make the membrane
more permeable, and allow the stain to better enter the cell. Many fixatives are used,
but a common one is ethanol. You are going to compare toluidine blue staining of
fixed and unfixed cells of the cyanobacterium, Anabaena.
Unfixed cells:
Mix one drop of toluidine blue with one drop of Anabaena suspension directly on a
slide. Cover it with a coverslip, and examine it under 40X.
Can you see the cell wall? (It should look like a pinkish fringe around the cell)
Describe:
Fixed cells:
Place one drop of Anabaena suspension on a watchglass, and add one drop of 50%
ethanol.
Mix well and leave for 2-3 minutes, then transfer one drop of this mixture to a slide,
and add one drop of toluidine blue. Mix and leave for 2-3 minutes to stain.
Transfer 1 drop of stained suspension to a new slide, cover it with a coverslip, and
examine it under 40X. If you need to move to 100X, add a drop of immersion oil on
top of the coverslip.
What are the main features you see?
What are the main differences between this slide and the unfixed cells?
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Make a drawing of both fixed and unfixed cells. Label features that you can identify,
and indicate size with a scale (Figure 6)
Figure 6:
Write a brief explanation of the difference between the two slides.
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6.
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7.
The following questions are to be attempted in your own time prior to todays lab, and
will be graded (very poor to very good) by your demonstrator during this lab. These
questions will conribute up to 1% of your final grade.
Question 1
Using a diagram, briefly describe what is meant by the domains of life. What
cellular characteristic was used to construct the phylogenetic tree depicting
the domains of life?
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Question 2
Using diagrams, explain the theory of endosymbiosis:
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SECTION 2:
EXPLORING CELL FUNCTION
PRACTICALS 4 - 6
Over the next three practical classes, your mission will be to perform accurate and
repeatable measurements of cell functions including:
Graduate attributes
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PRACTICAL 4
CELL FUNCTION I
OSMOSIS AND DIFFUSION
ASSESSMENT
Your group enzymes project experimental protocol is due today. A hard copy of your
groups protocol (based on the template provided via Moodle), signed by all members
of the group, must be submitted to your laboratory demonstrator at the
commencement of todays practical class.
OBJECTIVES
o To calculate and report on parameters involved in diffusion through a semipermeable membrane
o To investigate and report on the effects of osmosis on animal and plant cells
CONTENTS
1.
2.
3.
Osmosis
Effect of osmosis on animal and plant cells
Post-lab discussion - Accuracy, precision & reproducibility
1.
OSMOSIS
Introduction:
Movement of substances through cell membranes can, at one extreme, be entirely
dependent on physical factors (passive transport) or at the other extreme, may be
entirely dependent on specific transport mechanisms that require energy for their
function (active transport).
One of the most important factors influencing the passive movement of substances
through cell membranes is membrane permeability. All cells are enclosed by a
plasma membrane which is semipermeable. To be more accurate, the plasma
membrane is selectively or differentially permeable to various solutes. Osmosis is the
spontaneous net movement of water across such a semi-permeable membrane from
a region of low solute concentration to one with a high solute concentration, down a
solute concentration gradient. These descriptions all imply that the cell membrane is
much more permeable to water than it is to most solutes dissolved in the water.
The net movement of a solvent (substance, usually a liquid, in which other
substances are dissolved) is from the hypotonic (less-concentrated) to a hypertonic
(more-concentrated) solution. This results in a reduced difference between the
concentrations.
79
Experimental Procedure:
NOTE: Congo red will stain skin and clothing indelibly.
Work in pairs
In this part of the experiment, you will demonstrate osmosis using an artificial semipermeable membrane, and calculate the osmotic potential. The osmotic potential of a
solution that is separated from another solution by a semi-permeable membrane is a
measure of potential of the solution to suck water across the membrane.
Take a 10 cm length of dialysis (cellophane) tubing. Wet the ends of the tubing.
Insert a solid rubber bung into one end of the tubing and a perforated rubber bung
into the other end. Wrap one or two rubber bands tightly around each of the rubber
stoppers to make a leak-proof seal at each end of the dialysis tubing.
Over the sink, carefully fill the bag through the hole in one of the bungs with 3.5% w/v
Congo red solution (i.e. 3.5 gm Congo red in 100 mL aqueous solution).
The molecular weight of Congo Red is approximately 700. What is the molarity of
the Congo Red solution?
Insert the capillary tube into the hole in the bung until the red solution appears at the
bottom of the tube above the bung. Do not bend the capillary tube. Hold the tube
close to the end being inserted through the bung and take care to apply force only
along the axis of the capillary tube. Wash the outside of the filled dialysis tube with
water to remove any spilled Congo red solution.
Examine the apparatus for leaks.
Support the capillary tube on a retort stand so that the capillary tube is vertical and
the dialysis bag is completely immersed in a beaker of distilled water, as illustrated in
Figure 1 on the following page.
80
Figure 1.
Note the level of the Congo red solution in the capillary tube.
Measure the level every 20 minutes for the next 2 hours and plot the results against
time on the blank graph provided as Figure 2 (dont forget to give the figure a title).
81
Figure 2:
82
Use Equation 1 below to calculate the osmotic pressure exerted by the congo red
solution under these circumstances. Show your calculations.
Equation 1:
Where:
= 1000 RT (Ci Co )
Use Equation 2 below to calculate the height of water that can theoretically be
supported by this solution. Show your calculations.
Equation 2:
Where:
P = gh
83
Given sufficient time, would the liquid column in the capillary tube reach this
height? Explain your answer:
Look at the demonstration using 2% methyl blue as the osmotic agent instead of
congo red. The molecular weight of this molecule is almost the same as congo red.
Can you think of a reason why Methyl blue readily escapes from the dialysis bag
while Congo red does not?
84
2.
Two solutions containing different solutes but having the same osmotic pressure are
called iso-osmotic. However, if these two solutions are separated by a membrane
they may not exert the same osmotic pressure across the membrane. This will
depend on the permeability of the membrane to each of the two solutes. When two
such solutions do exert the same osmotic pressure in a membrane system they are
described as being isotonic. Osmotic potential depends on solute concentration and
temperature whereas tonicity depends on solute concentration, temperature and the
relative permeability of the membrane to the solutes.
In the next exercise, the effect of osmotic gradients on animal and plant cells will be
demonstrated by lysis (bursting) of animal erythrocytes (red blood cells) and by
plasmolysis (cytoplasmic shrinkage) of plant cells.
Animal erythrocytes:
To measure the tonicity of animal erythrocytes (red blood cells) you will set up a
series of salt solutions of differing tonicities, and you will see whether the
erythrocytes lyse or not.
Set up a series of 10 labelled test tubes in a test tube rack.
Use the pipettor to dilute the stock 0.2 M (200 mM) sodium chloride (NaCl) provided
with distilled water to make up the range of solutions given in Table 1. Your tutor will
demonstrate the correct use of the pipettor.
Table 1. Concentrations of Sodium Chloride (NaCl)
Tube
Volume of
Volume of dist.
Final NaCl
NaCl (mL)
water (mL)
conc. (mM)
1
1.25
3.75
50
1.50
3.50
60
1.75
3.25
70
2.00
3.00
80
2.25
2.75
90
2.50
2.50
100
2.75
2.25
110
3.00
2.00
120
3.25
1.75
130
10
3.50
1.50
140
Result
(lysis or no lysis)
85
Solute permeability
In this experiment, you will investigate the effect of solute permeability into
erythrocytes on the outcome of the lysis process, remembering that unless the solute
can penetrate the erythrocyte membrane, osmosis cannot occur. All the solutions
you will use are 330 mM. A range of different solutions, including sucrose, glucose,
urea, glycerol and ethyl alcohol are provided.
Decide what factors might affect the permeability of different solutes into
erythrocytes. Explain your reasoning:
Choose two solutions from those available, making sure you choose one that you
think will easily penetrate the cells, and one which will not. Make sure that at least
one person within your bench group will be testing every solution.
Place 2 mL of each of your solutions into separate small test tubes. Add 2 drops of
blood to each tube and quickly stir.
86
Using a stop watch if necessary, note the time taken for complete lysis of the
erythrocytes.Keep checking your tubes at 1 minute intervals for the first 10 minutes,
then 5 minute intervals for one hour if necessary.
Record the time taken for lysis in each of your tubes. Consult with the other
members of your bench group, and complete the table of the time taken for lysis
upon exposure to each solution (Table 2).
Table 2: Estimation of induced lysis of erythrocytes
Solution
Time until complete lysis of erythrocytes
Were the erythrocytes affected by the different solutions in the ways that you
predicted? If this was not the case, can you suggest reasons for this?
87
The average osmotic concentration of the intracellular fluid of the population of plant
cells can be estimated using the phenomenon of plasmolysis.
Plasmolysis occurs when the osmotic potential gradient is reversed by placing cells in
a hypertonic solution. Water then diffuses out of the vacuole into the external
solution. Incipient plasmolysis describes the condition when a solution removes
sufficient water to cause the protoplast to detach from the cell wall.
The concentration that causes plasmolysis in 50% of the cells can be estimated by
placing pieces of plant tissue into a graded series of solutions. This concentration is
isotonic with the vacuolar contents of an average cell in the tissue.
You should work as a bench group for this experiment. Each student should perform
counts on at least two tubes.
Note: Students are advised to put gloves on when handling Rhoeo because the plant
can be an irritant.
Cut 9 thin slices from the purple epidermis on the underside of the Rhoeo leaf. Note:
any slice that has numerous green photosynthetic cells attached to its under-surface
is too thick. Immerse the slices in distilled water as they are cut.
Set up a series of 8-10 labelled specimen tubes.
You will now use the pipettor to dilute a 0.5 M (500 mM) NaCl solution with distilled
water to a range of concentrations from 500 mM down. Make sure you cover the
range well so you can narrow down the concentration that is isotonic with the plant
vacuole.
You need a total volume of 10 mL in each tube, so use the table below to help you
calculate the relative volumes of NaCl and water you need for each concentration.
For example, if you wanted to test NaCl at 500 mM, you would add 10 mL NaCl
solution and 0 mL distilled water. If you wanted to test 250 mM, you would add 5 mL
NaCl solution plus 5 mL distilled water. Complete Table 3, to indicate the range of
concentrations you will test.
88
Volume of NaCl
(mL)
Volume of distilled
water (mL)
Show your table to your demonstrator. While there is no one correct answer for the
appropriate concentrations of NaCL to use, your tutor will review your calculations for
the dilutions.
Before placing any pieces of plant epidermis into the tubes, mount one slice in
distilled water on a microscope slide with the cuticle uppermost, and cover with a
cover-slip.
Select two tubes from your series, one from the highest half of the dilutions series,
one from the lower half, e.g. you might choose tubes 1 and 5, or 2 and 6 etc.
At 3 minute intervals, totally immerse one of the slices of epidermis in one of your
tubes, and leave for 20 minutes.
After 20 minutes, remove each piece, and mount it in the solution in which it was
soaking on a microscope slide with the cuticle uppermost, and cover it with a coverslip.
Immediately examine at least 50 cells for plasmolysis. Any cell showing visible
separation of the purple protoplast from the cell wall should be counted as
plasmolysed.
89
Record the total number of cells you count, and the number of these that are
plasmolysed.
From this, calculate the percent plasmolysed at each NaCl
concentration.
Obtain the results from other members of your group, and record all in Table 4.
Table 4: Results
Tube
NaCl
concentration
(mM)
Total no.
cells
counted
No. of cells
plasmolysed
% cells
plasmolysed
90
Figure 3:
91
What occupies the space between the plasmolysed protoplast and the cell wall
of the Rhoeo cells?
92
3.
Reproducibility and accuracy are the essence of science. Your data needs to be:
Reliable/reproducible: if you repeat the measurement several times under the
same conditions you should get the same answer.
Accurate: your measurement should give you the correct value or very close to it.
An unreliable method cannot be accurate, but reproducibility does not guarantee
accuracy.
Can you think of an occasion where a reproducible measurement might not be
accurate?
Activity:
Practical use of calibrate pippettes.
93
PRACTICAL 5
CELL FUNCTION II
PHOTOSYNTHESIS AND RESPIRATION
OBJECTIVES
o To investigate the effect of light intensity on the rate of photosynthesis
o To determine the rate of respiration in mung beans and the effects of different
metabolic inhibitors on that rate.
CONTENTS
1.
2.
3.
4.
Photosynthesis:
1a. Rate of photosynthesis and light intensity in a whole plant
1b. Structure of a chloroplast
1c. The Hill reaction
Respiration
Post-lab discussion
Major theme study questions II
1.
PHOTOSYNTHESIS
Introduction:
Photosynthesis is frequently defined as the process by which green plants
manufacture carbohydrates from carbon dioxide and water, using radiation from the
sun as a source of energy. The overall process is summarised by the equation:
carbon dioxide + water
6CO2 + 6H2O
glucose + oxygen
C6H12O6 + 6O2
94
The so-called dark reactions are reactions in which carbohydrates are made from
carbon dioxide by using the reducing power of the ATP and NADPH generated in the
light reactions. Since production of carbohydrates can occur with or without light, it is
perhaps misleading to call it the dark reaction, and the process is better termed the
Calvin cycle. Only the light reactions are unique to photosynthesis. You will look at
this part of the process today.
1a
Demonstration:
This experiment using the aquatic plant Egeria densa has been set up as a
demonstration. The rate of photosynthesis at different light intensities was measured
by the rate of oxygen production, as indicated by the rate of bubbling. Other factors
that might affect the photosynthetic rate were kept constant. The data are set out
with the demonstration. These light measurements were made on the axis of the
lamp, in the centre of the beam. They do not follow the inverse square law because
the lamp and reflector are not a point source over these distances.
Why is the relationship between photosynthetic rate and light intensity
curvilinear with a tendency to saturate at higher light intensities?
95
1b
STRUCTURE OF A CHLOROPLAST
Figure 1: Chloroplast.
1c.
96
Since the oxidising agent used by plants in intact chloroplasts is NADP+, the light
reaction can be written as:
2H2O + 3ADP + 3P + 2NADP+ O2 + 2NADPH + 3ATP + 2H+
Hill used an artificial oxidising agent, ferric cyanide. Modern versions of the reaction
use an oxidising agent called dichlorophenolindophenol (DPIP for short) in place of
NADP. So the Hill reaction can be written as:
2H2O + 2DPIP*
light
97
Trial run:
Wrap a thin sheet of foil around each of two test tubes. Leave them in a test tube
rack. Label the tubes A and B. To A add 6 mL of buffered sucrose solution and 0.5
mL of 2,6 dichlorophenolindophenol (DPIP, strength 0.4 mmol.L-1). To tube B add
6.5 mL of buffered sucrose solution.
Half-fill a beaker to act as a water bath. Place the test tube holder in the beaker, with
2 empty tubes (the rubber rings are for the bottom of the tubes, so they stay upright).
Direct a 240 V 60 W bench lamp onto the tubes at about 10 cm distance from them
(that is, 10 cm from the rim of the lamp holder to the test tubes), but keep the light
turned off. Check that your light is in a direct line with the tubes.
Add 0.5 mL of your chloroplast suspension to each of tubes A & B and stir the
mixture. Quickly remove the foil from tubes A and B. Remove the empty tubes from
the holder in the H2O bath and replace with tubes A and B.
Turn on the light. Start the timer and time the disappearance of the blue colour from
the tube containing DPIP (e.g. when the tube containing DPIP is the same green
colour as the control tube).
Which reaction leads to this change in colour?
10
15
20
40
60
200
200
200
200
200
98
Express your results as a graph (Figure 3). Make sure your graph is fully labelled and
accurately represents the data in the table.
What can you conclude from this experiment?
What is the role of tube B? Is it effective in this role? If not, what would you
suggest in its place?
99
Figure 3:
100
2.
RESPIRATION
Introduction:
In its broadest meaning, respiration means the release of energy from complex
organic molecules built up during the process of photosynthesis. The overall process
can be summarised as:
101
102
Dampen the sides of the rubber bung with water and insert it with its plastic tube
firmly into the test tube.
Attach the pinch clamp to the rubber tubing, but do not clamp it yet. A millimetre
scale is firmly attached to the plastic tube.
Set up the respirometer in a horizontal position on the stand.
Affix the flat-bottomed tube containing the dye solution to the other end of the plastic
tubing so that the end of the plastic tubing is about one centimetre from the bottom of
the tube containing the dye.
Keep your respirometer away from heat sources, as it is very sensitive to heat.
Allow your experiment to equilibrate for about 5 minutes, and then tighten the clamp.
Wait several minutes until the end of the dye column reaches the millimetre scale.
Take the initial reading for your experiment.
Over the next seventy five minutes, take readings of the location of the liquid at 3
minute intervals. Compare your results with the demonstration of sterilzed beans set
up in the laboratory.
At the end of your experiment, the dye column can be returned to the flat-bottomed
reservoir container by opening the pinch clamp and tilting the plastic tube. Blow any
droplets of dye solution remaining in the plastic tube onto a piece of paper towel
using compressed air from the tap at the front of the laboratory.
Analyse your results as follows:
The internal diameter of the plastic tubing is 3.0 mm. Use the formula for the volume
of a cylinder to calculate the volume of gas consumed in the tube at each time point.
Record your results in Table 5.
Plot a graph (Figure 6) of your experimental results on the graph provided over the
page, showing the cumulative volume of gas consumed in the tube at three minute
intervals. Make sure that your graph is well labelled and that the data correspond to
those in your table.
Compare your results with those of other groups.
How reproducible are your results? How can you evaluate this?
103
Was there a difference in the oxygen consumption of the fresh and sterilised
mung beans? If so, can you explain this?
Did you observe water vapour within the respirometer? Where may this water
have come from?
104
Table 2.
Time (min)
3
6
9
12
15
18
21
24
27
30
33
36
39
42
45
48
51
54
57
60
63
66
69
72
75
105
Figure 6:
106
4.
The following questions are to be attempted in your own time prior to todays lab, and
will be graded (very poor to very good) by your demonstrator during this lab. These
questions will conribute up to 1% of your final grade.
Question 1
Using diagrams, explain the flow of electons which occurs in the light dependant
reactions of oxygenic photosynthesis:
107
Question 2
Cellular respiration allows organisms to extract energy from food. List and briefly
describe the main stages of cellular respiration within a eukaryotic cell. Include
references to the cellular locations of these stages and use diagrams to illustrate
your answer where possible:
108
PRACTICAL 6
CELL FUNCTION III
ENZYMES
ASSESSMENT
Today you will be carrying out the experimental procedures designed by your project
group to investigate enzyme activity. The experimental notes, results and
observations that you record today will be checked and assessed by your
demonstrator at the end of the practical (see below for details).
CONTENTS
1.
2.
3.
1.
After your demonstrator has shown your group where to locate all the necessary
reagents and equipment required for your experiment, you can get started!
Use the following blank pages to write experimental notes, observations and raw
data/results for your experiment. If more space is required, write on separate sheets
of blank or lined paper and secure these to your manual, preferably using a stapler.
NOTE: All experimental notes, raw data and observations will be checked, signed
and marked on an individual basis by your demonstator at the end of this laboratory
class. It is your responsibility to ensure that you have written down everything in your
own manual and that you are not relying on other group members to collect the
information.
109
Demonstrator Signature:
Date:
110
Demonstrator Signature:
Date:
111
Demonstrator Signature:
Date:
112
Demonstrator Signature:
Date:
113
2.
One of the skills you need for this course is the ability to write a clear, concise and
well-referenced report of your experimental results and how you achieved them.
While there are specific requirements for a scientific report, the ability to write a clear
report will be of benefit to you whatever career you undertake.
Introduction and Aims:
Your aim should be based on your hypothesis, and tell your reader what it is that you
are trying toachieve with your experiment. You should also provide an introduction to
your reader that tells them what other researchers have done in this area of work
(citing references of course). Never assume that your reader knows the work as well
as you do!
Methods:
When you design an experiment, you need to be sure of 2 things:
The method you use will work.
The methods you use will give you a result that means something.
The essence of a good scientific finding is that you or other people can get the same
result when they do the same experiment, i.e. it is reproducible. Because very small
differences in the way you do an experiment can affect your results, you must provide
your reader with enough information about your methods that they can do exactly the
same experiment. this can include telling them where you bought reagents, at
exactly what temperature and for what times you carried out procedures, and even
what machines you used.
Results:
In this section, you should identify what you found in your experiment. You need to
show your exact data (not an approximation) and this can be in the form of a graph or
a table: make it as easy as possible for your reader to understand what you have
done and what the result is. You need to label your table or graph to make it even
clearer. You should also describe in words your experiment and what its result was.
For example, the following table shows the result of an experiment to determine
whether six different cells have a nucleus and/or organelles.
Table 1: Presence of organelles in different cell types
Cell origin
human cheek
Bacterial culture
Onion smear
Lettuce leaf
Raw steak
Nucleus
yes
no
yes
yes
yes
Mitochondria
yes
no
yes
yes
yes
Chloroplasts
no
no
yes
yes
no
114
3.
Using data collected as a group, you must now work individually and compile a
scientific report that is to be written and presented in a style similar to that of a
primary scientific research article. In this report, you must describe the background
details of your allocated enzyme and the hypothesis that you were testing, along with
a thorough explanation of the materials and methods that you used, the experimental
method employed, your experimental results, and a discussion of the experimental
outcomes and observations. (See below for a detailed description of the report
structure and requirements).
Remember that each member of your lab group must write and submit their own
experimental report.
The report is to be submitted as a separate document, and should include a cover
page with all the necessary details completed. (Group Assignment cover sheets can
be downloaded from the Assessments section in Moodle).
Enzymes Report due date:
Your report is due at the beginning of your lab class in Practical 8 and is worth 15%
of your final assessment mark in BABS1201.
The penalty for late reports is 10% per day, including weekends.
115
Report structure:
Below are some guidelines for the structure and content of your report, including an
approximate distribution of marks for each section. Approximate page lengths are
also provided for each section, but please note that your group will not be penalised
for exceeding these where it is necessary to do so.
Introduction (1 mark)
Approximately 0.5 to 1 page in length
The Introduction should include:
A brief and general description or definition of enzymes and enzyme function.
A more detailed description of the specific enzyme you examined in your
experiment.
A clear explanation of the hypothesis and aim(s) of your experiment, with
reference to the type of results you expected to obtain and what they might tell
you about enzyme structure and/or function.
Materials and methods (2 marks)
No longer than 1 page in length (not including diagrams)
This section should be similar to the protocol you have already submitted to your
demonstrator, except that it should include any changes or modifications to your
original experimental plan. Your Materials and Methods section should include:
A concise list of all reagents and equipment used in your experiment.
A complete description of the experimental procedure in the form of a list of all
the experimental steps performed by your group as performed on the day
(that is, include any deviations to your original protocol).
Optional: you might also like to include diagrams to depict one or more of the
steps in your experimental procedure.
If you have adapted your protocol from another source such as the internet,
you must make a reference to this here.
Results (2 marks)
Approximately 1 to 2 pages in length
The Results section should include:
Tables and/or graphs of the data your group collected during your experiment.
A brief description of the results, including any additional observations that
were made on the day. The purpose of the results section is to accurately and
effectively communicate your results to the reader, and not to interpret them
specifically this is instead the purpose of the Discussion section of your
report.
116
Discussion (4 marks)
Approximately 2 to 4 pages in length
The Discussion section should include:
A more thorough description of your results with respect to the aim(s) of your
experiment. Did you expect the results you obtained and observations that you
made? If not, why do you think your experiment did not proceed as expected?
What were the major sources of possible error in your experiment?
An answer to the following question: what do your results/observations tell you
about enzyme structure and/or function?
Comments on how your experiment might be improved if you or someone else
were to repeat it.
Reflective comments describing the experience gained in designing and then
implementing your own experimental protocol (for example: the difficulties that
were faced, the valuable insights that were gained, etc.).
References (1 mark)
The References section should include:
A complete list of any internet sites, textbooks or other references that you
used to design your experimental protocol.
Any other references such as journal articles or text books that you may have
obtained information from for the purpose of writing your introduction,
discussion or any other part of your report.
We recommend that you use the Harvard referencing style (or something very
similar to this) for your reference list and internal citations.
Report Checklist:
Any material used from other sources is cited in the text, and given in full
detail in References.
The reference list should be only of references cited in the text - it is not a
bibliography.
Both tables and figures should be included in the results section of the
report.
Tables, graphs and drawings are given a title, and are clear and
unambiguous.
Text should be no smaller than 10pt type (Figure legends no smaller than
8pt).
117
SECTION 3:
EXPLORING GENES
PRACTICALS 7 - 9
Your mission in this section is to explore:
The mechanisms by which DNA is passed from cell to cell when they divide.
The third and final sequence of practical classes involves three labs exploring
aspects of cell division, genetic inheritance, and molecular biology related to the
concepts that will be discussed in lectures.
With the publishing of the human genome (all the genes in a human), and of multiple
genomes of other living organisms including mice, dogs, horses, many plants, many
bacteria and viruses, and many protists, modern genetics is one of the most
important basic sciences supporting modern biological research. It is on some of the
important concepts underlying genetics that this section is focussed.
The goals for this sequence are:
Graduate attributes:
Your assignments for this section of the course can be included in your portfolio as
evidence of the following Science Graduate Attributes:
118
PRACTICAL 7
GENES I
MITOSIS AND CELL DIVISION
OBJECTIVES
o Describe human karyotyping and its role in ascertaining sex and detecting
chromosomal abnormality.
o List and explain the principal events in mitosis and meiosis.
o Define the following terms: diploid, haploid, homologous chromosomes,
locus, alleles.
o Explain the difference between the first and second meiotic divisions.
o List and explain the similarities and differences between meiosis and
mitosis.
o Define the following terms: heterozygous, homozygous, dominant and
recessive.
CONTENTS
1.
2.
3.
4.
1.
Introduction:
The production of new cells continues throughout the life of any multicellular plant or
animal. Unless there is some mishap, each cell divides to produce two exact genetic
replicas of itself. This is the result of a process called mitosis, the division of the
chromosomes. The chromosomes are located in the nucleus, and they contain the
DNA, which carries the genetic information. The genes controlling a specific
characteristic, for example, eye colour, are always at the same place (locus) on a
specific chromosome.
Understanding mitosis (and meiosis) is important for understanding how genetic
information is passed from a cell to its daughter cells.
We will follow the behaviour of these chromosomes through a complete cycle of cell
division. Although it is a continuous process, mitosis is divided into stages for
convenience. These stages, which can be recognised down the microscope, are
named as follows: prophase, metaphase, anaphase, telophase.
Successive mitotic divisions alternate with a much longer interphase. Diagrams and
photographs of each stage are placed around the laboratory. For more detail on each
of these phases, see the textbook.
119
Figure 1: The cell cycle. G1 is the first growth phase, and G2 is the second
growth phase.
Human karyotype:
A diploid human cell usually contains 46 chromosomes, consisting of 23 homologous
pairs. One of the homologous pairs are the sex chromosomes (XX in females or XY
in males). The non-sex chromosomes are called autosomes. The karyotype of a
species describes the chromosome complement of an organism in terms of
chromosome number and length, centromere position and any other characteristics
such as banding patterns seen with certain staining methods.
Many human hereditary defects caused by chromosomal abnormalities can be
identified by examining human chromosomes from cells that have been arrested in
metaphase of mitosis a stage when chromosomes are very short and compact.
Leukocytes (white blood cells) or fetal cells obtained by amniocentesis or chorionic
villus sampling are often used for diagnosis.
The cells are cultured (to increase their number), treated with a chemical that disrupts
the mitotic spindle (to stop mitosis), and placed in a hypotonic salt solution (to swell
their nuclei). (Note: the mitotic spindle is a structure made of microtubules, which
coordinates the movement of chromosomes during cell division).The mixture is then
centrifuged (to increase the concentration of cells) and transferred to a glass slide. As
a drop of the cell suspension hits the slide, the nuclei break open and the
chromosomes spread apart; usually chromosomes from a single cell remain in an
identifiable group. The cells are then stained using procedures that result in banded
chromosomes.
In the early days of studying the human karyotype, it was hard to tell individual
chromosomes apart. So they were classified into seven major groups, A through G.
These groups were based on their length and the position of the centromere (the
constricted point on the chromosome). The groups were:
Group A
Group C
Group E
Group G
Chromosomes 1-3
Chromosomes 6-12
Chromosomes 16-18
Chromosomes 21 and 22
120
121
2.
In todays lab you will be given a root tip of an onion plant. It was fixed (killed) by a
mixture of acetic acid and alcohol and soaked for a short time in 70% ethanol to clear
the cytoplasm of oil droplets and other material that might make the chromosomes
difficult to see. It was then stained in aceto-carmine and stored in 45% acetic acid.
This procedure destroyed the spindles and stained the chromosomes red.
Preparing a root tip squash:
This technique will be demonstrated in a video.
Place a root tip on a microscope slide and cover it with a drop of 45% acetic acid, the
mounting medium.
If the root tip is thick, split it lengthwise. Keep one half on the present slide and
transfer the other half to a drop of 45% acetic acid on a second slide. Thus, two
slides can be made from one tip.
Hold the cut end of the root with a pair of forceps and cut off about 1 to 2 mm of the
pointed tip, the deeply stained meristem, with a sharp razor blade. Discard the
remainder of the root.
Cut the 1 to 2 mm of the tip remaining on your slide into 3 or 4 pieces. Spread these
in the drop of acetic acid containing gum chloral to prevent drying out.
Cover the tip with a cover-slip. Avoid all movement of the cover slip from now on.
Hold the edge of the cover-slip with your fingers and tap the surface firmly with the
blunt end of a pencil, dissecting needle or forceps to spread the cells - the red blobs
of tissue should spread into pink smears.
Place the slide, cover-slip down, on a tissue then fold the tissue over the slide. Hold
both ends of the slide firmly with one hand, and use the thumb of the other hand to
press on the centre of the slide. It helps squash the cells if you roll your thumb
slightly as long as you do not move the slide about.
Examine the whole preparation under the lowest power of the microscope and
identify interesting cells.
What makes a cell interesting? Can you see the chromosomes, and can you
identify cells at different stages of the cell cycle?
If the cells are not in a single layer, repeat the previous step. Switch to 40X objective
and study the cell in detail. Return to low power when searching for other stages.
122
This will speed your work immensely. Remember that you need to continually adjust
the focus when using high power.
In the spaces below, draw a cell at metaphase (Figure 2) and a cell at anaphase
(Figure 3). Write captions for your drawings and label them fully, including the
following where appropriate: centromere, sister chromatids, daughter chromosomes.
Sister chromatids are the two copies of a chromosome produced through DNA
replication during S phase. They are attached to each other at the centromere until
they separate during anaphase.
Figure 2:
Figure 3:
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3.
MEIOSIS
Introduction:
Sexual reproduction allows the genes of two individuals to combine and provides the
variability upon which evolution can work. In sexually reproducing organisms, the
production of sex cells, or gametes, requires that each parent's chromosomes be
reduced to half the normal number.
This halving of the parent's chromosome number from the diploid, or 2n, number to
the haploid, or n, number is the result of meiosis. Combining two haploid (n) gametes
during fertilization then restores the chromosome number to the number that is
characteristic of the diploid (2n) organism (Figure 4).
fertilisation
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Diploid parent
nucleus with two
chromosomes
DNA duplicates
Each
chromosome
consists of two
chromatids
Daughter cells
contain half the
number of
chromosomes
characteristic of
parent cell
Meiosis 1
First nuclear
division
Chromosomes
separate
Meiosis II
Second nuclear
division
Haploid
daughte
r cells
Chromatids
separate
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Experimental procedures:
You can study the process of meiosis using a chromosome simulation kit. The
yellow and red strands of beads, both of the same length, represent two
homologous chromosomes. A yellow strand represents the contribution of one
parent and a red strand represents the contribution of the other parent. In other
words, the yellow and red chromosomes are a homologous pair. The second yellow
and red strands in your kit are to be used as chromatids for each of these
chromosomes.
Interphase
Place one strand of red beads and one strand of yellow beads near the centre of
your work area. (Recall that chromosomes at this stage would exist as diffuse
chromatin and not as visible structures.)
Position the two hollow, cylindrical beads at right angles to each other near the
chromosomes. These hollow beads represent a pair of centrioles, which are
structures at the poles of cells involved in cell division.DNA synthesis occurs during
interphase prior to meiosis, and each chromosome, originally composed of one
strand, is now made up of two strands, or sister chromatids, joined together at the
centromere region. (Within the centromere region where two chromatids are most
closely associated, a platelike protein structure called the kinetochore is attached to
each chromatid. Spindle fibre microtubules attach to the kinetochores during
division.) A chromosome composed of two chromatids is called a dyad (or bivalent).
Simulate DNA replication by bringing the magnetic centromere region of the second
red strand into contact with the centromere region of the first red strand. Do the
same with its homologue, the yellow strand (Figure 6).
126
Centriole replication also takes place prior to division. Use two additional cylindrical
beads to simulate centriole replication. Place these next to the two original centriolar
bodies or centrioles.
Meiosis I
Prophase I
Homologous chromosomes come together and synapse (closely apply themselves to
each other), pairing along their entire length. Here, you should recognize the first
major difference between mitosis and meiosis.
Did homologous chromosomes synapse during prophase of mitosis?
A tetrad, consisting of four chromatids or two dyads, is formed. Entwine the two
chromosomes as shown in Figure 7.
Sister chromatids
Non-sister chromatids
(a)
(b)
You will not include crossing-over in this simulation, but you should be aware that it
can happen during prophase I.
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The centrioles that replicated prior to division begin to move to opposite sides (poles)
of the nucleus as the nuclear membrane breaks down.
Separate the two pairs of centrioles and move them to each side of the
chromosomes (Figure 7a). Spindle fibres also appear during prophase. You will not
simulate spindle fibres. Imaginary spindle fibres are shown as dotted lines in all
diagrams.
By the end of prophase I, each tetrad can be clearly seen to contain four separate
chromatids. Sister chromatids are linked at their centromere, while non-sister
chromatids that have crossed over appear to be held together at X-shaped locations
called chiasmata (singular, chiasma) (Figure 7b).
Metaphase I
Chromosomes have untwined by this time and can now be seen as dyad
chromosomes. They now line up in the centre of the cell in homologous pairs.
How does this arrangement of chromosomes differ from that in metaphase of
mitosis?
Position the chromosomes near the midpoint between the centrioles and at right
angles to the imaginary spindle fibres extending from the centrioles (figure 8).
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Figure 10: Telophase I homologues are found at opposite ends of the cell.
These may be separated into two cells by cytokinesis. In most organisms,
centrioles duplicate at this stage.
Compare the amount and arrangement of genetic material in each cell following
telophase of meiosis and telophase of mitosis.
How many of each type of chromosome do you see per cell? How many chromatids
does each chromosome have?
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Meiosis II
The following simulation procedures apply to bothchromosome groups (daughter
cells) produced by meiosis I.
Interphase II (Interkinesis)
The amount of time spent "at rest" following telophase I depends on the type of
organism, the formation (or not) of new nuclear membranes, and the degree of
chromosomal unwinding. Because interphase II does not necessarily resemble
interphase I, it is often given a different name-interkinesis. DNA replication does not
occur during interkinesis. The lack of DNA replication in this phase represents a third
major difference between mitosis and meiosis.
Prophase II
Separate the pairs of duplicated centrioles and tape them down on opposite sides of
each chromosome group (Figure 11).
Figure 11: Prophase II duplicated centrioles move to opposite poles in the two
daughter cells. Chromosomes shorten and thicken.
Does this action duplicate what you did during prophase I of meiosis?
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Metaphase II
Orient the chromosome so that it is centreed between the centrioles during
metaphase II (Figure 12).
Anaphase II
Sister chromatids now appear to be more loosely associated at the centromere
region. When completely separated, each chromatid will have its own centromere
region and can be referred to as a chromosome.
Separate the sister chromatids of the chromosome and pull the new daughter
chromosomes toward the centrioles on opposite sides of each daughter cell (Figure
13).
131
Telophase II
Pile each chromosome near its centriole. Formation of a nuclear membrane and
division of the cytoplasm, cytokinesis, occur at this time (Figure 14).
Figure 14: Telophase II-- four haploid daughter cells are formed following
cytokinesis. New nuclear membranes are formed within each daughter cell;
one pair of centrioles is present outside the nuclear membrane. (a) Simulation.
(b) Cells.
How many cells have you formed during the process of meiosis?
If the same set of chromosomes with which you began this simulation exercise
were to undergo mitosis, would the resulting cells be haploid or diploid?
132
PRACTICAL 8
GENES II
GENETIC INHERITANCE
GENETIC SCREENING BY POLYMERASE CHAIN REACTION 1
ASSESSMENT
Your group scientific report on the Group Enzymes Project (20%) is due today. You
must submit a hard copy of your groups report directly to your demonstrator at the
commencement of todays lab class.
OBJECTIVES
o Define and explain Mendel's law of segregation (the 1st law).
o Apply Mendel's first law to a simple cross between two heterozygous
individuals.
o Demonstrate the alternative possible arrangements of homologous
chromosomes during metaphase I of meiosis.
o Relate the arrangement of homologous chromosomes in metaphase I to the
number of types of genetically different gametes that can be produced.
o Define & explain Mendel's law of independent assortment (the 2nd law).
o Verify that the law of independent assortment holds true for alleles in a
dihybrid cross between two heterozygous individuals.
o To successfully prepare samples for PCR.
CONTENTS
1.
2.
3.
133
During meiosis, homologous chromosomes are separated from each other, and only
one may be carried in a particular gamete or spore. Thus the gene copies carried on
each of the homologous chromosomes are also separated or segregated.
When a diploid is heterozygous, this segregation is significant because the haploid
gametes carry different alleles. Mendel's first law states that alleles segregate in
meiosis(Figure 1). When two haploid gametes combine during fertilization, two alleles
for each trait are again present in the offspring.
134
Experimental Procedure:
Repeat the meiosis simulation performed in Practical 7, but first take a piece of label
tape and mark one bead on each yellow strand (chromatid) as A (same location on
each strand). Mark one bead on each red strand as a. Make sure that A and a
appear at the same locus on the two homologues (Figure 2).
Explain:
You have just demonstrated that during meiosis the two homologous genes for any
trait segregate so that each ends up in a different gamete or spore.
135
What is the phenotype of the offspring in this generation (which is labeled F1)?
will
136
The consequences of this segregation of alleles will become apparent when one
examines the possible genotypes in the next generation (called F2 since it is
composed of the offspring produced by F1 individuals).
The possible combinations of alleles that may be produced in each parent's
gametes, and the results of these combinations in the genotypes of the offspring,
can be determined by using a table called a Punnett square. All of the possible
genotypes of gametes that can be produced by one parent are listed across the top
of the square; all genotypes of gametes that can be produced by the other parent
are listed along the side.
In the Punnett square below, one type of gamete from each F 1 parent has already
been listed, and one possible combination is shown. Fill in the blanks for the other
gamete genotype for each parent, and then complete the other three combinations
in the square to determine the possible genotypes of the offspring. (Note: By
convention, the dominant allele for each trait is written first: for example, Vv, not
vV.) Below the Punnett square, list the genotypes and phenotypes of the four
types of individuals produced in the F2 generation.
Gametes from
mother
VV (full)
Vv (full)
Genotype
Phenotype___________
________
____________________
________
____________________
________
____________________
________
____________________
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Heterozygous
Homozygous
recessive
Genotype
Proportion
In the table below, fill in the expected proportion of individuals showing these
phenotypes
Phenotype
Full wing
Proportion
Short wing
Your demonstrator will supply you with a photograph simulation of randomly selected
F2 flies.
Record the total number of flies and then record number of flies with full size wings
and those with short wings.
Full wings
Short wings
Your data
Class total
How do these numbers compare to the proportion you predicted?
138
139
Figure 4: Mark alleles at the same locus on each chromatid and on homologous
chromosomes.
If you begin with two pairs of homologous chromosomes, there are two possibilities
for their alignment during metaphase I of meiosis, depending on which side you
place the yellow and red homologues. Draw both of these possibilities in Figure 5.
Indicate the alleles present on each chromosome.
Follow possibility 1 through meiosis, using the red and yellow beads. As you
proceed through your simulation for possibility 1, figure out how the chromosomes
and alleles would be distributed in possibility 2.
In the spaces provided in the diagrams in Figure 5, draw the chromosomes as they
appear for both possibilities at all stages indicated. Use coloured pencils to show the
colour of each chromosome at each step. Always indicate the alleles present on
each chromosome. Your demonstrator should check your bead setup for metaphase
I and metaphase II.
140
Possibility 1:
Possibility 2:
Prophase 1
Prophase 1
Metaphase 1
Metaphase 1
Anaphase 1
Anaphase 1
Figure 5.
141
Possibility 1 (continued)
Figure 5. (continued)
Possibility 2 (continued)
142
You have now demonstrated Mendel's second law: alleles of unlinked genes assort
independently.
How many possible combinations of alleles exist if you consider the results from
both possibilities?
Mendels second law can be verified by tracing the fate of two unlinked genes in
Drosophila through a series of crosses. In addition to the locus for wing length (with
alleles V and v) there is a locus that controls eye colour (with alleles S and s).
Homozygous recessives (ss) have white eyes, while the other two genotypes have
the dominant wild-type colour of red with a black glint in the centre. Suppose you
cross a VVss mother with a vvSS father. This is called a dihybrid cross.
Which alleles are present in the gametes of these parent types?
Find the possible genotypes that would be present in individuals of the F1 generation
by filling in the Punnett square below.
Gametes from
father
Gametes from
mother
143
Use the Punnett square below to find the proportions of different genotypes in the F2
progeny resulting from all the possible unions of the various gametes produced by
the F1 generation.
_______
_______
_______
_______
Gametes from
mother
_______
_______
_______
Circle all genotypes that result in a particular phenotype with the same wing size and
eye colour.
Indicate the expected proportions (ratios) of individuals showing the following
phenotypes:
144
Take another look at your flies (from the photograph simulation), particularly their
eyes. Observe the number of flies with red eyes and those with white eyes. Now
record the number of flies that have a) full wing + red eye, b) full wing + white eye, c)
short wing + red eye, and d) short wing + white eye, and add your data to the class
total.
Full wing +
white eye
Full wing +
red eye
Short wing +
white eye
Short wing +
red eye
Your data
Class total
Do your results support what you predicted from the Punnett square? Explain:
2.
Aim:
The aim of this experiment is to introduce you to some molecular techniques that are
used in medical diagnostics.
Perhaps the most important of these is PCR (Polymerase Chain Reaction), which
allows the amplification of specific gene sequences in any DNA sample, such as
those collected for forensic and diagnostic screening. You will use this technique to
screen some DNA samples for deletions in the Duchennes Muscular Dystrophy gene
and determine a family pedigree for this disease. You will also precipitate DNA from
an aqueous solution probably the most commonly performed technique in a
molecular lab.
145
Background:
In the last few years, the Polymerase Chain Reaction (PCR) has become a very
widely used technique in Molecular Biology. This technique enables the selective
amplification of a desired DNA sequence. The process involves thermal cycling and
DNA synthesis from oligonucleotide primers (see Figure 6).
In thermal cycling there are three different temperatures per cycle - a denaturation
step which separates the DNA strands (usually 92 - 95C); a step where the
oligonucleotide primers anneal to the DNA template (generally 50 - 65C); and a step
at 72C where the oligonucleotide primers are extended by Taq DNA polymerase.
These three temperatures constitute one cycle and usually 25 - 35 cycles are used in
each experiment.
The oligonucleotides provide the specificity for the reaction. They are usually
between 20 and 30 bases in length, which is sufficiently long to hybridise (base pair)
at only one sequence in the human genome. The oligonucleotides are synthesized
chemically in an automatic machine.
Taq DNA polymerase is used because it is stable at high temperatures (92 - 95C)
and its temperature optimum is 72C. It was originally isolated from a bacteria
growing in thermal hot springs.
The PCR exponentially amplifies a DNA sequence. This is because in each cycle
the number of DNA strands doubles and hence over a million-fold amplification can
occur in 25 cycles. (See Figure 1 over page). In 1g of human DNA (whose haploid
genome contains 3 X 109 bps of DNA), a unique sequence of 300 bp comprises
0.1 pg of DNA which is too small a quantity to be seen on an agarose gel (of course it
would be indistinguishable from the rest of the genome). If the 300 bp sequence can
be selectively amplified a million-fold by PCR, then the 0.1 g can be visualized on
an agarose gel. This can be accomplished in an afternoon by the PCR technique.
DNA sequence:
The sequence that you will be attempting to amplify is an exon sequence from the
Duchennes Muscular Dystrophy (DMD) gene. Within this particular family pedigree,
there has been a deletion of approximately 200 bp within the coding sequence.
Following PCR amplification of the specific DNA sequence, deletions of this size can
be readily identified by agarose gel electrophoresis. Based on the experimental
results you should be able to complete a pedigree for this family and determine the
carriers and affected individuals and hence, the mode of transmission.
146
147
Procedure:
Within a demonstrator group, you want to analyze the DNA from every member of
the pedigree. Ensure that each student within your group has a different DNA
sample to analyze so that all the DNA samples are analyzed (there are a total of 15
DNA samples to be analyzed in this pedigree).
1. Pipette 20l of DNA into a 0.2 ml PCR tube.
2. Add 4 l of PCR mix.
This consists of (final concentration in 25 l):
2 pmole forward oligonucleotide primer
2 pmole reverse oligonucleotide primer
200 M dATP, 200 M dCTP, 200 M dTTP, 200 M dGTP
16.6 mM (NH4)2SO4
67 mM Tris-HCl, pH 8.8 (at 25C)
6.7 mM MgCl2
3. Add 1 l of Taq DNA polymerase (supplied by your demonstrator).
4. Mix the contents of the tube by gently flicking the tube with your finger. Clearly
label the tube with your initials and give the tube to your demonstrator.
5. The tube will be placed in the PCR machine for thermal cycling and will be
returned to you at the next practical class.
6. Record here exactly what you did, including any mix-ups that might affect your
results: you will not be penalised for these, but the information is necessary to
interpret results properly next week.
148
3.
Introduction:
Once you have the data from your PCR experiment next week, you will use it to
analyse a family pedigree. A study of human genetics is complicated by the fact that,
unlike other species of animals or plants, our species is not bred experimentally and
test crosses cannot be made to order. One of the principal tools is the pedigree, a
phenotypic record of a family extending over several generations, showing whether
each individual is affected by some condition. We can use a standard format for
such a pedigree so that everyone can understand it. A standard set of symbols is
used in the pedigree shown in Figure 7.
marriage line
unaffected
female
unaffected
male
offspring line
II
affected
daughter
unaffected
daughter
outsider
affected
son
III
unaffected
grand-son
unaffected
grand-daughter
Each individual is identified by the generation, and the relative order of appearance
within that generation. Hence III 2 is the last individual shown in this pedigree.
Affected means that the individuals show some unusual condition, and symbols for
these individuals are shaded in the pedigree. Shading over only half of a symbol
indicates individuals who are known heterozygotes (carriers).
149
Table 1.
150
Female
151
Table 3.
Total
Male
Female
Widows peak
(a V-shaped hairline above the forehead)
Cleft chin
(a Y-shaped furrow on the chin)
Mid-digital hair
(hair on the middle joints of the fingers: may be
very fine)
Ear lobes
(the lobes of the ears can be free or attached:
record those attached)
Tongue rolling
(the ability to roll ones tongue into a tube)
Darwins tubercle
(a small lump on the rim of the external ear)
Can you make any suggestions as to the mode of inheritance of any of these
traits? Explain:
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PRACTICAL 9
GENES III
GENETIC SCREENING BY POLYMERASE CHAIN REACTION 2
CONTENTS
1.
2.
3.
4.
5.
Practical exam
Completion and analysis of screening PCR
Precipitation of genomic DNA from peas
Post-lab discussion
BABS1201 Science fair presentations
1.
PRACTICAL EXAM
The practical exam (comprising the first hour of todays class) will require you to
demonstrate profiency in the following techniques:
I. Microscopy
II. Plotting and interpretation of data
III. Accurate use of precision instruments
2.
Identification of hazards:
There are some potential low-level risks associated with this practical class as
follows:
Chemical Hazards
Biological Hazards
Human DNA
Procedural Hazards
Overview:
Following amplification of an exon from the DMD gene by PCR last week, you now
need to visualise the amplified DNA fragments. This is accomplished by separating
the DNA fragments using agarose gel electrophoresis and staining the samples to
visualise the DNA. You will prepare the gels, load your DNA, run the gels and
visualise the DNA.
153
Background
Due to its repetitive structure, native double-stranded DNA has a constant charge per
unit length and, on average, a constant mass per unit length. DNA molecules,
because of their identical shape, will migrate in an electric field at a rate inversely
proportional to their length or mass. Consequently, one of the simplest and most
rapid means of separating DNA fragments of varying sizes is by electrophoresis in an
agarose gel using an alkaline buffer.
The DNA fragments are highly negatively charged and so migrate to the positive
electrode. Agarose is a complex mixture of polysaccharides isolated from seaweed.
When the agarose is heated in solution it will form a gel as it cools (like jelly). The
agarose provides a matrix where the pore size can be varied depending on the
percentage agarose in the gel. For example, a 0.7% gel will separate kilobase sized
fragments whereas a 1.5% gel can be used for fragments 100 1000 base pairs
(these are very general estimates). The gels are usually produced as a horizontal
slab (approx. 4mm thick) with GelRedTM used to detect the DNA. GelRedTM is a dye
molecule that binds to nucleic acids and produces a luminescence under ultraviolet
light. Very small amounts of DNA (less than 100ng) can be detected by this method.
It is possible to estimate the size of DNA fragments by observing the distance of
migration relative to the migration of standard DNA molecules of known size.
Procedure:
Agarose gels will be prepared for you before the class.
You should perform the following steps. Each bench group should have two gels.
If not already done so, place the gel in the electrophoresis tank. Make sure that the
top of the gel (the end with the comb) is next to the negative electrode (black) i.e.
NOT at the end with the positive electrode.
Add enough running buffer to just cover the gel.
Carefully remove the comb from the gel and ensure that buffer enters the wells that
have been formed when the comb was removed. There should be no air bubbles in
the wells.
Add 5 l of gel loading buffer (GLB) to your PCR sample.
Set the pipettor to 6 l and gently pipette the DNA/GLB mixture up and down to
ensure they are completely mixed.
Pipette 6 l of this mix into the wells in the gel. Make sure you make a record of
which sample is loaded in which lane.
In the middle lane of the gel, load the molecular weight markers (labeled M).
When all the samples are loaded, place the lid on the electrophoresis apparatus and
attach the electrodes to the power supply using the leads provided. Make sure that
the top of the gel is attached to the negative electrode (black) so that the negatively
154
charged DNA will migrate through the gel to the positive electrode.
Run the gel (at 100 volts) until the bromophenol blue marker dye has migrated half
way.
While this is happening, perform the DNA precipitation (part 2 of this practical).
With the aid of your demonstrator, visualise the DNA in the gel using the Gel
Documentation system.
Analysis:
Estimate the size of the bands on the agarose gel, using the molecular weight
markers as a guide. The sizes of the marker bands are: 1000, 800, 600, 500, 400,
300, 200, 150, and 100 base pairs, with an additional faint band at 50 base pairs.
With this information, you should be able to determine which individuals in the
pedigree have a complete exon and which have a deletion. Use this to complete the
following pedigree.
II
1
III
1
IV
4
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3.
Although DNA is packed so efficiently into cells that we cannot see it, it is possible to
isolate DNA from cells and precipitate the DNA from solution so that it is visible.
Indeed DNA can be isolated from almost any organism, including the food we eat
(provided it hasnt been cooked!).
DNA has been prepared for you from peas by using high salt solution and detergent
to lyse the cells, extract the nuclei, and release the DNA into solution.
You will precipitate the DNA from this aqueous solution by the addition of cold
alcohol.
Pipette approximately 1 ml of the aqueous DNA solution into a clean specimen tube.
Using the 1 ml disposable plastic pipette, slowly add 2 ml of cold 95% ethanol. Let
the ethanol run down the side of the tube so that it forms a layer above the aqueous
DNA solution.
Using the pipette gently stir the layer where the ethanol touches the DNA solution.
You should observe the formation of long fibrous strands of DNA.
If you are careful, you should be able to pull the DNA out of the test tube by gently
swirling the pipette in the DNA layer and then pulling it through the alcohol layer
What colour is your DNA?
Pure DNA should be translucent. If it is whitish in colour then it still has some
proteins (called histones) attached to it.
Why does DNA appear stringy?
If you want to keep the DNA, gently ease it off the end of the pipette into a vial of
50% ethanol. Cap the vial tightly. In the PCR you used GelRedTM to visualise your
DNA under UV light.
What do you see? Are they the same or different?
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4.
Introduction:
Today's activity will be conducted according to the think, pair, square model. Initially
each student should individually consider the question for about 5-10 minutes. The
students should then pair up and further explore the question for another 5-10
minutes. Then finally the whole group should come together.
Topic:
What investigations should be undertaken if we are to decide whether or not male
and female sporting competition should be restricted to people who are XY and XX
respectively?
157
5.