Virtual Lab Questions

SBI4U VIRTUAL LAB QUESTIONS
Name: ________________________________
Go to the website http://learn.genetics.utah.edu/content/labs/. You will be looking at five different

virtual labs. They are DNA Extraction, Gel Electrophoresis, PCR, DNA Microarray and Flow
Cytometry.
DNA Extraction Lab (6 marks)

1. What are three reasons that you would need to do genetic testing of DNA?
Genetic testing, analysis of forensic evidence, body identification.
2. a) Why do people typically use mouth swabs in order to conduct genetic testing?
Skin on the inside of the mouth loses thousands of cells each day so these cells can be easily
obtained and then DNA in these cells isolated and tested.
b) Why might this be used instead of a blood sample?
Blood is mainly comprised of red blood cells that do not contain DNA.
3. Why do we need proteinase K?
To break down the histone proteins the DNA is wrapped around to unravel it.
4. Why do you think the cells were placed in a warm water bath when the lysis solution was
added?.
The enzymes that will break down the proteins need activation energy which the warm
water will provide.
5. a) For the first centrifuge - Why would the DNA be in the liquid portion after putting the tube
into the centrifuge instead of in the pellet at the bottom?
The centrifuge causes denser things to gather at the bottom so the cell debris and proteins settle at
the bottom and since the DNA is all broken up, it is not as dense and remains distributed in the
solution.
b) For the second centrifuge – Why would the DNA now sink to the bottom of the tube?
The isopropyl alcohol causes the DNA to gather in dense clumps so it will now sink the bottom in
the centrifuge.
Gel Electrophoresis Lab (4 marks)

1. What is the purpose of the gel?
The gel acts as a filter that will allow smaller fragments on DNA to move through it faster
than longer fragments, showing approximately how many base-pairs long a fragment of
DNA is.
2. Why does the DNA move through the gel?

The DNA is negatively charged so it is repelled from the negative charge on one side of the gel and is
attracted to the positive side and moves towards that side through the gel.
3. When making the agarose gel, what is the comb used for?
To make the wells in the gel to put the DNA solutions in.
4. Why do we stain the gel after we run the gel electrophoresis?

Staining the sorted groups of DNA helps to make them visible to the naked eye.
PCR Lab (8 marks)

1. What does PCR do?
It isolates a certain fragment of DNA and copies it over a billion times.
2. Why would PCR be effective to help in analysis of crime scenes?
PCR is effective to help in crime scenes because you can use a sample of blood, saliva, hair, etc and
find a marker on this DNA and compare it to the suspects to confirm who was or wasn’t involved in
a crime. You only need a small sample because PCR would replicate the DNA many times to obtain a
good sized sample to test.
3. What is the purpose of the extreme heat (approximately 95oC) used on the DNA?
The heat is used to separate the two strands of DNA by breaking the hydrogen bonds.
4. Why do the DNA strands not reanneal

Th DNA strands want to reanneal but there are more primer sequences than DNA molecules in the
solution so the primers lock on to their target/complementary sequences before the DNA can
reattach.
5. How do the primers help to isolate desired DNA fragments? Why does it take 3 cycles
The primers only attach to either the beginning or end of the desired fragment and mark the
starting point of DNA polymerase. Because of this, all the nucleotides upstream of where the DNA
polymerase begins will not get replicated. The first cycle results in 2 DNA molecules missing all the
sequences upstream of the desired segment. The second cycle results in 2 molecules with 1 original
strand and one strand missing all the nucleotides on 1 side of the desired fragment and 2 more
molecules with 1 strand missing all nucleotides on 1 side of the desired fragment and 1 strand with
only the desired fragment. Finally, in the third cycle, 2 molecules of isolated desired fragments are
produced and as the cycle continues these molecules quickly become the majority.
6. Why do your DNA fragments multiply to such a large number in just 30 cycles?
Each fragment doubles in each cycle so in thirty cycles you would have 2^30 or over a billion
fragments.
DNA Microarray Lab (9 marks)

1. Why has it been difficult in the past for scientists to study the full human genome?
Humans have around 20,000 genes and it would take a very long time to investigate each gene, one
at a time.
2. Why would some of your body cells express genes that others would not?
Different types of cells have different requirements and it would waste resources to turn on
all genes all of the time so cells only have the genes they need turned on.
3. How can a microarray help to treat cancer?

Microarrays show the differences in gene expression between two cells so scientists can
compare healthy cells to cancerous ones to determine which genes are turned on/off that
shouldn’t be in the cancer cells to diagnose and treat cancer better.
4. Why would you want to isolate mRNA instead of DNA?
You would want to isolate mRNA because the best way to tell whether a gene is being expressed or
not is to see if it is making mRNA transcriptions. If there is an mRNA transcription of a gene it is
most likely being expressed and if there is not then it is not being expressed.
5. Why doesn’t the DNA stay in the solution after the first centrifuge?
DNA strands are much, much longer than RNA strands so they sink to the bottom.
6. How do you separate mRNA from tRNA and rRNA?
Pouring the solution through a column filled with poly-T beads that will only bind to the
poly-A tails that are exclusively found in mRNA, allowing rRNA and tRNA to flow through.
7. Why would you add a labelling mixture?
The mRNA is converted to DNA because DNA is more stable. Labelling the DNA will show
which genes are from the cancer cells and which are from the healthy cells.
8. Why would hybridization with a probe be a useful tool in genetic engineering?

Hybridization is a useful took in genetic engineering because it can be used to add new
genes, regardless of the source, to form recombinant DNA which can be used for many
purposes.
9. What is a major limitation to this technology?

This technology shows gene expression by comparing the presence of mRNA for a gene but RNA
expression doesn’t always indicate protein activity therefore not all gene defects show up on a
microarray.
Flow Cytometry
1. What three things can you use flow cytometry for? (1 mark)
Complete blood count, diagnose leukaemia, look for signs of cancer after treatment.
Introduction to blood: (2 marks)
a. What is the liquid portion of blood called?

The liquid portion of blood is called the plasma.
b. What are the scientific names for the three types of blood cells?
Thrombocytes, Erythrocytes and Leukocytes.
c. Which one is in the highest proportion?

Erythrocytes/ red blood cells.
d. What could cause a white blood cell count be raised (think about it)?
Some sort of infection that would require white blood cells to fight it.
Complete Blood Count (CBC) (6 marks)
a. What information would a CBC test give?

Proportions of different types of blood cells in the blood.
b. What are two methods for conducting a complete blood count?
Manual and automated blood analyzer.
c. Why would a blood analyzer be preferable?
An automated blood analyzer is more preferable because it’s much faster and more
accurate.
d. How does the flow cytometry count the cells?

Cells will flow one at a time and pass through a laser beam. As a cell flows through the laser
it scatters the light which will be detected by the light detectors and counted, larger cells
disrupt more light than smaller ones and cells with more internal complexity will have more
side-light scattering.
e. What are the differences between the two scatterplots?
The patient has less lymphocytes and neutrophils than a normal person and many
immature white blood cells where a normal person has none.
Diagnosing Leukemia (5 marks) : Write a paragraph on how flow cytometry is used to diagnose
leukemia and to check for remaining disease after treatment.
Flow cytometry is an essential technology in the diagnosis of leukemia and checking for
remaining cancer after treatment. Acute leukemia is when stem cells in bone marrow divide
uncontrollably and immature white blood cells do not mature properly and overcrowd other types
of cells. Flow cytometry can be used to do a CBC to show the proportions of types of cells in the
blood and if there are too many/too little of a certain type of cell, leading to a diagnosis of leukemia.
It can also help choose the proper treatment by identifying the specific type of cell that is growing
out of control. To find this out, T-cells are tagged orange and B-cells are tagged blue. When the cells
in the sample pass through the laser they will scatter either blue or orange light and by plotting
this, scientists can conclude which type of leukemia a patient has and what the best treatment is.
After treatment, flow cytometry is used again to see if any cancer remains. If there is detectable
cancer a different treatment will be used and if there is no detectable cancer it means that the
treatment is working and will be continued.

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SBI4U VIRTUAL LAB QUESTIONS

Go to the website http://learn.genetics.utah.edu/content/labs/. You will be looking at five different

DNA Extraction Lab (6 marks)

Genetic testing, analysis of forensic evidence, body identification.

b) Why might this be used instead of a blood sample?

3. Why do we need proteinase K?

Gel Electrophoresis Lab (4 marks)

2. Why does the DNA move through the gel?

4. Why do we stain the gel after we run the gel electrophoresis?

PCR Lab (8 marks)

It isolates a certain fragment of DNA and copies it over a billion times.

2. Why would PCR be effective to help in analysis of crime scenes?

4. Why do the DNA strands not reanneal

DNA Microarray Lab (9 marks)

3. How can a microarray help to treat cancer?

4. Why would you want to isolate mRNA instead of DNA?

6. How do you separate mRNA from tRNA and rRNA?

7. Why would you add a labelling mixture?

8. Why would hybridization with a probe be a useful tool in genetic engineering?

9. What is a major limitation to this technology?

a. What is the liquid portion of blood called?

c. Which one is in the highest proportion?

Complete Blood Count (CBC) (6 marks)

a. What information would a CBC test give?

d. How does the flow cytometry count the cells?

e. What are the differences between the two scatterplots?

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