Download THE CELL - Kevan Kruger

THE CELL
Types of Cells
Prokaryotic cells (pro = first and karyotic = nucleus)
These were the first cells. They were primitive, small, had
no defined nucleus (no nuclear membrane), and no
membrane bound cell organelles at all.
Eukaryotic cells (Eu = true and karyotic = nucleus)
These are modern cells. They have a nucleus and
membrane-bound organelles. They are much
larger (up to 1000X larger).
Cell Theory:
All living things are made up of cells
The cell is also the functional unit of life
All living cells come from pre-existing cells
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Cell Structure
The cell is the basic unit of life
contains internal structures called
organelles.
and
Cell Organelles
1. Cell membrane: This is a universal
structure. It is the same in all
organisms. It is also the same as most
internal membranes of the cell.
of the
The cell membrane is composed of a bi-layer of phospholipids with
proteins embedded in it. The model used to explain the cell
membrane is called the FLUID MOSAIC model.
2. Nucleus: The nucleus is the control
centre of the cell. It is large, and
centrallylocated It is surrounded by a
double layered membrane with
pores, it contains DNA. This is where
transcription and replication occur.
The nucleus has two functions.
It contains the genetic information
It directs all cell activities through
protein synthesis
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It is made up of the following things:
Nuclear membrane: a double layer of cell
membrane, which contains very large pores which
allow macromolecules (RNA and proteins) in and
out of the nucleus.
Nucleolus: This is the dark stained area in
the nucleus (usually spherical). It is made up
primarily of RNA. It is not membrane bound. It makes rRNA
(ribosomal RNA), which then makes ribosomes. It is involved in
protein synthesis.
Chromatin: strands of DNA densely coiled together with histone
proteins. Chromatin is condensed into chromosomes during cell
division. Chromosomes contain all of the genetic material
(DNA/genes) for the cell/organism.
Nucleoplasm: this is the cytoplasm of the nucleus.
It supports and suspends the contents of the nucleus.
3. Mitochondria: This is the FURNACE of the cell, and is located in the
cell cytoplasm. It is a double membraned structure where the ce area.
Mitochondria are used to convert the chemical energy in food to
biological energy for use by the cell (ATP – adenosine triphosphate).
inner membrane is highly infolded into cristae to increase inner
surfaMitochondria have their own DNA.
Mitochondria performs Cellular Respiration:
C6H12O6 + O2  CO2 + H2O + ATP energy
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4. Endoplasmic Reticulum: This is an extensive network of internal
sheets of cell membrane. The ER connects the nuclear membrane to
the plasma membrane.
There are two types:
Smooth ER: contains no attached
ribosomes. sER make lipids and steroids. SER
also detoxifies harmful material or waste
products (there is lots of smooth ER in liver
cells).
Rough ER: A series of tubular canals
connected in places with the nuclear
membrane. There are ribosomes attached to
the membrane of the rER. The Rough ER assists in the production of
proteins to be exported out of cell. Proteins are transported inside
the E.R. to the Golgi apparatus.
5. Ribosomes: These are small dense stained granules that are made of
rRNA. Ribosomes are the site of protein synthesis and they ensure the
correct order of amino acids and make a peptide bond. Ribosomes are
typically attached to the rough ER (so proteins produced can be easily
exported), but will attach to any membrane or float in the cytoplasm
(free floating groups of ribosomes are called POLYSOMES). Polysomes
produce proteins to be used inside the cell.
Ribosomes contain two
subunits; one big, one small.
They are found in both
prokaryotic and eukaryotic
cells.
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6. Golgi Body (Apparatus): These are made up of flattened saccules of
cell membrane, which are stacked loosely on top of
each other. Their function is to receive and
temporarily store proteins from the rough ER. These
proteins are packaged into membrane enclosed
vesicles which pinch off from the edges, and are
distributed within the cell or shipped to the cell membrane for
excretion.
7. Vacuoles and Vesicles: These are the storage sacs of the cell
membrane. Vacuoles are larger and are formed by
phagocytosis (cell eating). Vesicles are smaller
and are formed by pinocytosis (cell drinking);
often formed from the Golgi apparatus or from infoldings of the cell
membrane. They are both used to import and export substances from
the cell that need to be separated from the cytoplasm, and both store
food, water, and/or waste.
8. Lysosomes: These are double membraned vacuoles containing lytic
(digestive) enzymes that can break down proteins and
lipids. Lysosomes are produced by the golgi body. They
are also known as ‘suicide-sacs’. Their function is to attach
to food vacuoles and digest their contents, and to enable
an organism to destroy old or malfunctioning cell parts. They are also
used as a cell defense system as they are capable of dissolving
bacteria.
9. Cilia and Flagella: These are hair like projections,
which use energy to produce movement. (cilia - short
and many, flagella - long and few).
cilia
They are made up of ‘microtubules’,
which have the universal structure of
‘9+2’. Both have a basal body (‘9+0’
structure) at their base in the
cytoplasm to act as an anchor. Their
function is cell locomotion.
flagella
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10.
Centriole: A pair of basal bodies that grows
spindle fibers, which attach to and move
chromosomes during mitosis. These are found in
animal cells only.
11. Cytoskeleton: This gives the cell its shape and form. It anchors
and supports the cell organelles. There are two components to the
cytoskeleton:
Microfilaments: long and extremely thin
protein fibres that occur in bundles, which
are made of 2 proteins called Actin and
Myocin. Organelles may move around the
cytoplasm on these.
Microtubules: These are
larger than microfilaments.
They are cylinder shaped and
made of a coiled protein called
tubulin. They are used to make cilia, flagella,
centrioles and spindle fibres.
12. Cytoplasm: This is a ‘watery gel’ that contains mainly water with
dissolved salts, proteins and other organic compounds. It’s functions
are to support and suspend organelles and to provide water for all of the
cells biochemistry.
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