BIOL111 Plant Cell Structure Lecture Notes
BIOL111 Plant Cell Structure Lecture Notes
BIOL111 Plant Cell Structure Lecture Notes
THE CELL
Cells are the structural functional unit of living structures. The overall function of the
body is actually the combined function of all these cells. Within these cells the
complex biochemical and physical processes necessary for maintenance and
reproduction of life are carried out.
ROBERT HOOKE
• Reported that thin slices of cork and other plant materials contained minute
partitions separating cavities that he named “cells”. What he saw were
empty cavities and it was not until 1835 that:
• Discovered the microscope and £free cells£ with nucleus (red blood cells)
• Father of Microscopy
DUJARDIN
• Stated that any living body must have its parts of cellular tissue or formed by
such tissue.
ROBERT BROWN
ALEXANDER FLEMMING
cell theory
• Most of the cells are small, ranging from about 1-100 microns in diameter,
though some can be seen such as “yolks” of eggs of most vertebrates (fishes,
amphibians, reptiles, and birds) and some giant nerve cells of cows.
• Most of the cells are small due to the following reasons:
➢ The ratio of the volume of the cell’s nucleus to the volume of its
cytoplasm must not be so small than the nucleus in order for it to control
the cytoplasm.
➢ The need for cells o exchange nutrients and wastes with their external
environment through the plasma membrane.
o As a roughly spherical cell becomes larger, the innermost
regions become farther away from the membrane which makes
diffusion of substances a lot difficult and would take a relatively
longer time.
➢ Cell volume works to limit cell size
o As cell enlarges, its volume increases more rapidly than its
surface area does; so a larger cell has a greater need for
exchange of nutrients and wastes with the environment but a
relatively smaller surface area of the plasma membrane trough
which to make these exchanges.
o muscle cells and neurons can get very large due to their
elongated shape that increases their membrane surface area.
THREE STRUCTURAL PARTS OF A GENERALIZED ANIMAL CELL
PLASMA MEMBRANE
Components:
INCLUSIONS
• Temporary structures that contain secretions and storage products if the cell.
ORGANELLES
MITOCHONDRIA
• Universally present within animal cells except in mature red blood cells.
• Capable of self replication; that is, they divide to increase in number in
response to cellular need for ATP and cell division.
• Because of their function in generating ATP, an energy-rich molecule, they
are called the powerhouses or power generators of the cell.
Structure
• Are tiny spheres that contain ribosomal RNA (rRNA) and several ribosomal
proteins
• With large and small ribosomal subunits
• Site of protein synthesis
Some are free ribosomes and the others are attached to the ER (Endoplasmic
reticulum)
ENDOPLASMIC RETICULUM
o Rough ER (RER)
➢ Studded with ribosomes
➢ Functions:
✓ Protein synthesis
✓ Glycosylation or addition of carbohydrate groups to
glycoprotein.
o Smooth ER (SER)
➢ Has no ribosomes
➢ Functions:
✓ Triacylglycerols , phospholipids and steroid synthesis
✓ Drug detoxification (by hydroxylation or addition of OH
groups which increases solubility or hydrophobic drugs in
water so they can be easily excreted from the body)
✓ Carbohydrate metabolism (e.g. breakdown of glycogen by a
membrane-bound enzyme known as glucose-6-phosphate)
✓ Calcium storage (e.g. in muscle cells, sarcoplasmic
reticulum stores and releases calcium during relaxation and
contraction respectively)
GOLGI COMPLEX
➢ Ribosomes -> RER -> Transport Vesicles -> Golgi Complex ->
Secretory Vesicles -> Released to exterior of the cell by exocytosis.
LYSOSOMES
o Intracellular Digestion
➢ Lysosomal enzyme digest bacteria and other substances that enter
the cell in phagocytic vesicles (phagosomes) during phagocytosis,
pinocytic vesicles during pinocytosis, or endosomes during reporter-
mediated endocytosis.
o Autophagy
➢ Lysosomes also use their enzymes to recycle the cell’s own
structures. A lysosome can engulf another organelle, digest it, and
return the digested components to the cytosol to reuse. In this way,
old organelles are continually replaced. A human liver cell recycles
about half its contents every week.
o Autolysis
➢ Lysosomes act as “suicide bags” during apoptosis or “programmed
cell death” in which the cells themselves die in order to go about
normal development.
➢ E.g. during development of the vertebrate hand and foot, cells
between the digits die by apoptosis to generate free fingers and
toes.
o Extracellular Digestion
➢ Lysosomal enzymes released at sites of injury help digest cellular
debris, which prepares the injured area for effective repair.
PEROXISOMES
Functions
o HZOZ Metabolism
➢ Contain enzymes like oxidase that generate hydrogen peroxide and
catalase which degrades HZOZ; these enzymes are localized in the
same compartment to ensure that HZOZ would not harm cells.
o Detoxification of Harmful Compounds
➢ Catalase also detoxifies methanol, ethanol, formic acid,
formaldehyde, nitrites and phenols.
o Oxidation of Fatty Acids
➢ Peroxisomes shorten fatty acids in preparation for subsequent
metabolism in mitochondrion to produce acetyl coenzyme A.
CYTOSKELETON
o Microtubules
➢ Hollow, cylindrical structures 25nm in diameter assembled from the
protein called tubulin
Functions:
Functions:
• Both cilia (Latin for “eyelash”) and flagella (“whip”) are slender extensions of
the plasma membrane
• Both contain a ring of 9 fused pairs of microtubules, with an unfused pair of
microtubules at the center (forming “9+2” arrangement)
• Main difference between cilia and flagella lie in their length, number, and the
direction of force they generate.
o In general, cilia are short (about 10-25 microns long) and numerous;
they provide force in a direction parallel to the plasma membrane, like
the oars in a canoe; accomplished through a fairly stiff “rowing” motion
during the forceful power stroke and a flexible return stroke that bring
the cilium to its original position.
o Flagella are long (50-75 microns), relatively few in number, and provide
force perpendicular to the plasma membrane, like the engine of a
motorboat; flagella undulate with a continuous bending wavelike
motion, without distinct power-and-return strokes.
• Ciliated protozoans include Paramecium, Didinium, Euplotes, etc.
• Flagellated protozoans include Euglena, Trypanosma, and other
dinoflagellates
• Sperm cells and some spiral and rod-shaped bacteria are also flagellated
• Ciliated cells (e.g. in gills of oysters, oviducts of females, and respiratory
tracts of most land vertebrates) usually propel substances along their
surfaces.
CENTROSOME & CENTRIOLES
VACUOLES