Download Eukaryotic Cell Ultrastructure

Cell Biology &
Biochemistry
Series:Set 3
Version: 1.0
Objectives
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Learn the structure of eukaryotic cells.
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Structure to function of:
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Cell surface membrane
Nucleus
Mitochondria
Chloroplasts
Golgi apparatus
Lysosomes
Ribosomes
Rough Endoplasmic reticulum
Smooth Endoplasmic reticulum
Cell Wall
Vacuole
Features Shared by Plant
and Animal Cells
Organelles and structures found in both plant and
animal cells include:
Nucleus, chromosomes and nuclear envelope
Plasma membrane
Ribosomes
Mitochondria
Golgi apparatus
Endoplasmic reticulum (rough and smooth)
Vacuoles and Vesicles, although these differ
in size and function in plants and animal cells.
Animal & Plant Cells
Animal and plant cells have many organelles in common, as well as
several features specific to each. Specialized features of each are
labelled on the diagrams of a animal cell and an plant cell below.
Lysosome
Chloroplast
Centrioles
Cell
wall
Animal Cell
Plant Cell
Starch
granule
Nucleus
Located:
Variable location; not necessarily near
the center of the cell.
Nuclear pores
Structure:
Surrounded by a double nuclear
envelope and encloses the genetic
material (chromatin). Contains
nucleoplasm (a granular, jelly-like
material)
Function:
Contains most of the cell’s genetic
material as DNA,
Regulates all the activities of the cell Nuclear
membrane
and involved in protein synthesis
through production of RNA.
Size: 5 µm diameter.
Nucleolus
Chromatin
Nucleolus
Located:
Within the nucleus.
Depending on the organism, there
may be more than one.
Structure:
A prominent structure which
appears under EM as a mass of
darkly stained granules and fibers
adjoining part of the chromatin.
Function:
Synthesis of ribosomal RNA
Assembly of ribosomal
subunits.
Size: 1-2 µm diameter.
Nucleolus
The Nuclear Membrane/Envelope
The nuclear membrane
(or nuclear envelope) is a double
membrane, similar to the cell
plasma membrane.
Nuclear
pores
Outer
membrane layer
Inner
membrane layer
It encloses the nucleus to
separate its contents from the
cell cytoplasm.
The nuclear membrane has many
holes in it called nuclear pores
(3000 each 40-100nm).
The nuclear pores allow
the selective passage of
materials between the nucleus
and the cytoplasm.
This includes the movement
of mRNA into the cytoplasm.
Cell
cytoplasm
Nuclear
pores
Mitochondria
Located: Cytoplasm
Folded inner membrane
forms cristae
Structure: Rod shaped organelles occurring in
large numbers, especially in metabolically very
active cells.
Bounded by a double membrane; the inner
layer is extensively folded to form partitionsSmooth outer
membrane
called cristae.
Matrix
Cristae provide large surface area for the
attachment of enzymes and other proteins.
Mitochondria contain some DNA.
Matrix contains all the required substances
for reactions.
Function:
The site of cellular aerobic respiration (the
production of ATP).
Size: Variable but 1-10µm
A single mitochondrion in cross section
Plasma Membrane
Located:
Surrounds the cell forming a
boundary between the cell contents
and the extracellular environment.
Structure:
Semi-fluid phospholipid bilayer in
which proteins are embedded. Some of
the proteins fully span the membrane.
Phospholipid
bilayer
Protein
Function:
Forms the boundary between the cell
and the extracellular environment.
Regulates movement of
substances in and out of the cell.
Size: 3–10 nm thick.
The plasma membranes of two adjacent
cells joined with desmosomes
Ribosomes
Small subunit
Located:
Free in the cytoplasm or bound to
rough endoplasmic reticulum.
Structure:
Made up of ribosomal RNA (mRNA)
and protein and composed of two
subunits, a larger and a smaller one.
Function:
Site of protein (polypeptide) synthesis
Size: 20 nm.
Ribosomes
Polypeptides being produced
on a polyribosome system
Large
subunit
Polypeptide chain
Rough Endoplasmic
Reticulum
Located:
Continuous with the nuclear membrane
and extending to the cytoplasm as part of
the endomembrane system.
Structure:
A complex system of membranous tubules
studded with ribosomes. Connected to
the smooth ER but structurally and
functionally distinct from it.
Function:
Synthesis, folding, and
modification of proteins.
Transport of proteins through the cell.
Membrane production.
Size: Variable according to cell size.
Membranous tubules
Ribosome
Transport vesicle
budding off
Smooth Endoplasmic
Reticulum
Membranous tubules
lacking ribosomes
Located:
In the cytoplasm as part of the
endomembrane system.
Structure:
A system of membranous tubules
similar in appearance to the rough ER
but lacking ribosomes.
Function:
Synthesis of lipids, including oils,
phospholipids, and steroids.
Carbohydrate metabolism.
Transport of these materials
through the cell.
Detoxification of drugs and
poisons.
Size: Variable according to cell size.
Transport vesicle
budding off
Golgi Apparatus
Transfer vesicle from the ER
Cisternae
Located:
Cytoplasm, associated with the ER.
Structure:
Stack of flattened, membranous
sacs called cisternae.
Function:
Modification of proteins and lipids
received from the ER adding non-protein
component (eg carbohydrates).
Sorting, packaging, and storage of
proteins and lipids.
Transport of these materials in vesicles
through the cell.
Manufacture of some certain
macromolecules, e.g. hyaluronic acid.
Size: 1-3 µm diameter
Vesicle from the ‘shipping’
side of the Golgi
Vacuoles and Vesicles
Located:
In the cytoplasm; often numerous.
Structure:
Vacuoles and vesicles are both membranebound sacs, but vacuoles are larger.
Function:
food vacuoles in animal cells are formed
by phagocytosis of food particles.
central vacuole of plants provides cell
volume and stores inorganic ions and
metabolic wastes.
Support plant cells through turgor
pressure on cell walls
Vesicles transport substances out of the
cell through exocytosis
Size: varies according to
cell type and size.
Food vacuole in a
human lymphocyte
Specialist Plant Cell
Features
A small number of cellular organelles
are typically found in plant cells but not
in animal cells.
Organelles and structures found in
plant cells are:
cellulose cell wall
iStock
Chloroplasts
Amyloplasts
Cross section through a
buttercup stem showing
the individual cells
Cellulose Cell Wall
Located:
Surrounds the plant cell and lies
outside the plasma membrane.
Middle lamella
Structure:
microfibrils of Cellulose fibers,
with associated within a matrix.
Between the walls of adjacent
cells, is a sticky substance called
the middle lamella.
Function:
mechanical strength to
prevent cell bursting
maintains cell shape
Size: 0.1 µm to several µm thick.
Pectins
Hemicelluloses
Cellulose fibers
Diagrammatic representation
of plant cell wall structure
Chloroplasts
Located: Within the cytoplasm of plant leaf
(and sometimes stem) cells.
Grana
Stroma
Structure:
Specialized plastids containing the green
pigment chlorophyll.
Chloroplast envelope – selective double outer
membrane which are separated by a narrow
inter-membrane space.
Thylakoids
Inside the chloroplasts are stacks of flattened
sacs or thylakoids which are stacked together
as grana. Chlorophyll pigments inside thylakoid
absorb light.
Stroma is a fluid filled matrix where the second
stage of photosynthesis takes place.
Chloroplasts contain some DNA
Function:
The site of photosynthesis
Size: 2 -10 µm.
Specialist Animal Cell
Features
A small number of cellular organelles
are typically found in animal cells but
not in plant cells.
Organelles and structures found in
animal cells are:
lysosomes
cilia
flagella
TEM of a human lymphocyte
Lysosomes
Membrane proteins
Located:
Free in the cytoplasm.
Structure:
Single-membrane-bound vesicle of hydrolytic
enzymes (proteases and lipases). Lysosomes
bud off the Golgi apparatus.
Function:
Hydrolyse material ingested by phagocytic
cells such as white blood cells and bacteria
Release enzymes to outside of cell
(exocytosis) in order to destroy material
around cell
Digest worn out organelles and recycling of
cellular components (autophagy)
Completely break down cells after they have
dies (autolysis)
Size: varies according to cell size
Hydrolytic
enzymes break
down compounds
by adding water
Lysosomes in a
lymphocyte.
Note how they
are budding
from the Golgi
Plant Cell
Animal Cell
Homework
Read pages 67 – 71 and make a top trump card for each organelle
If you have any more information you
want to add then you can put it on
the back of the card
Chloroplast
Grana
Stroma
There is a Top Trump Template on
Moodle if you wish to print them off or
do it by computer.
Thylakoids
Job: Photosynthesis
Deadline for H/W Thursday Lesson.
Number of Membranes: 2
Special Structures: Thylakoids and Grana
Size: 2 -10 µm
Extension: Look at ‘Division of
Labour’ article on Moodle
Relative Sizes
The following scale shows the size range of some representative
cellular organelles, cells, and multicellular structures.
The scale is logarithmic to accommodate the range of sizes shown.
From left to right, each reference measurement marks a tenfold
increase in diameter or length.
Leaf tissue
DNA
Plasma
membrane
Animal cell
Plant cell
Golgi
Ribosome
Nucleus
Leaf
Cell Fractionation
Cell fractionation is the process where cells are broken up and the different
organelles are separated out.
Before cell fractionation begins cells are placed in a cold buffered solutions
of the same water potential (isotonic).
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Cold – to reduce enzyme activity that might break down organelles
Isotonic – to prevent organelles bursting or shrinking as a result of
water intake/loss
Buffered – so that pH does not fluctuate. Any change in pH may alter
protein/enzyme/organelle structure
Cell Fractionation
There are two stages to Cell Fractionation
1. Homogenation:
Cells are broken up by a homogeniser (blender). This breaks the cell
membrane and releases the organelles. The resultant fluid is known as
the homogenate and can be filtered to remove large debris and unbroken
cells.
2. Ultracentrifugation
The filtered homogenate is separated out in a machine called a
centrifuge. This spins very fast in order to create a centrifugal force.
Cell Fractionation
The process is as follows:
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The tube of homogenate is placed in a
centrifuge and spun at slow speed.
The harvested organelles, the nuclei, are
forced to the bottom of the tube, where they
form a sediment or pellet
The fluid at the top of the tube (supernatant) is
removed, leaving just the sediment of nuclei.
The supernatant is transferred to another tube
and spun in the centrifuge at a faster speed
than before
The next heaviest organelles, the mitochondria,
are forced to the bottom of the tube.
The process is continued in this way so that at
each increase in speed the next heaviest
organelle is sedimented and separated out.
Describe how you could use cell fractionation to isolate chloroplasts from
leaf tissue.
[3 marks]
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The suspension is filtered before spinning to remove debris / intact cells which would
contaminate sediment / interfere with the results.
Tissue is homogenenised to break open the cell and release the cell contents.
The solution is ice-cold because it slows / prevents enzymes being denatured.
It is isotonic to stop osmotic effects on cells / organelles.
It contains a buffer to prevent damage to proteins / enzymes due to changes in pH.
The second pellet collected is Chloroplasts
Organelles can be separated by centrifugation because they have different density.
Centrifuge at low speed to obtain nuclei as they are the largest / densest organelle.
Order of density from highest to lowest: nuclei, mitochondria, ER, golgi, ribosomes