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
Cell Structure
The cell is the basic unit of life and contains internal structures called organelles
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Cell Organelles
Cell membrane: This is a universal structure. It is the same in all organisms. It is also the same as most of
the internal membranes of the cell.
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.
Summary:
Composed of proteins and phospholipids (fats with Phosphorus).
Acts as skin around the cells contents.
Acts as a selectively permeable membrane to allow movement of materials in and out of the cell
Located around the outside of the cell.
Single membrane around the vacuoles, lysosomes, E.R., Golgi Apparatus.
Double membrane around the nucleus and mitochondria
Nucleus:
The nucleus is the control centre of the cell. It is large, and centrally located 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.
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It contains the genetic information
It directs all cell activities through protein synthesis
Summary:
Largest Organelle.
Surrounded by a double-layered
membrane (the nuclear envelope).
Membrane has pores through which
larger molecules pass. (Nuclear Pores)
Control center for the cell’s functions.
(The brain).
Contains a fluid called the nucleoplasm.
Contains chromatin (DNA strands which
forms chromosomes during cell division.
The nucleus 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.
Summary:
Dark region in the Nucleoplasm.
One or more found in the nucleus.
Site where ribosomal RNA (rRNA) is produced or stored.
Involved in interactions between the nucleus and the cytoplasm.
Chromatin:
strands of DNA densely coiled together with histone proteins. Chromatin is
condensed into chromosomes during cell division
The hereditary material of the cell.
Condenses to form chromosomes during cell division.
Composed of Protein and DNA.
Chromosomes contain all of the genetic material (DNA/genes) for the cell/organism.
o Rod-shaped bodies in the nucleus, particularly during cell division.
o Contains the hereditary information. (genes)
o Condensed chromatin
Nucleoplasm: this is the cytoplasm of the nucleus.
It supports and suspends the contents of the
nucleus.
Mitochondria:
This is the FURNACE of the cell, and is located in the cell cytoplasm. It is a double
membraned structure where the inner membrane is highly folded into cristae to increase inner surface area.
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Mitochondria are used to convert the chemical energy in food to biological energy for use by the cell (ATP –
adenosine triphosphate). Mitochondria have their own DNA.
Mitochondria performs Cellular Respiration:
C6H12O6 + O2  CO2 + H2O + ATP energy
Summary:
Burn glucose to produce ATP energy which is by cells to carry out specialized functions eg. Movement
Use up oxygen and give off carbon dioxide (this process is called cellular respiration).
Composed of two membranes.
Considered the powerhouse of the cell.
Their inner membranes loop back and fourth through the inner fluid, matrix, of the mitochondria increasing its surface area and
producing shelf-like structures called cristae.
This inner membrane is the site of cellular respiration.
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).
Summary of SER
o System of interconnected flattened tubes,
sacs, or canals.
o Begins at the nuclear envelope and
branches throughout the cytoplasm to the
cell membrane.
o Moves molecules from one are to another.
o Location of lipid manufacture. Cells that
produce steroid hormones, have an
abundant smooth ER.
o Section of both types of ER can break free “blebbing” to produce small membrane bound sacs of
either proteins or lipids called vessicles.
o Contains enzymes that synthesize lipids and related products such as steroids.
o Also seems to have enzymes that detoxify drugs.
o Amount of E.R. in a cell increases or decreases depending on the cell’s activity.
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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.
Summary of RER
o Like Smooth E.R., but with attached ribosomes.
o Abundant in cells that produce large amounts of protein for export from the cell.
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.
Contain rRNA and protein subunits.
Function as sites for protein synthesis.
Found on E.R. (proteins for export) or in cytoplasm. (Proteins for use in the cell).
Several ribosomes together in a line, all producing the same protein is called a polyribosome.
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.
Summary
o Stack, of a half dozen or more flattened sacs.
o On one side receives protein-filled vesicles from the E.R.
o Sorts the proteins and packages them in vesicles at the other
side.
o From here the vesicles more to different locations in the cell.
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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.
Vacuole
o
Vessicle
o
o
o
Storage areas for water, sugars, and salts.
A small vacuole
Storage sites in various kinds of molecules.
Can be made by the Golgi Apparatus or from an infolding of the cell membrane.
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.
o Special vacuoles formed by the golgi body. (double membrane)
o Contains powerful hydrolytic enzymes used to digest substances enteringthe cell or organelles that
are of no further use. (Autodigestions).
Cilia and Flagella:
These are hair like projections, which use energy to produce
movement. (cilia - short and many, flagella - long and few). 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.
Cilia
o Short, numerous, hair-like projections that are used for locomotion by many unicellular
organisms.
o Membrane – bound collections of microtubules ( 9 pairs arranged around a central pair
(called 9 + 2 pattern).
o Each pair of outer microtubules ( doublet ) also has pairs of arms projecting toward a
neighboring doublet and spokes extending toward the central pair of microtubules.
flagella
cilia
Flagella
o Like cilia but can be very much longer.
o Also for locomotion of organisms and gametes (sperm).
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.
o Very short cylinders with a 9 + 0 arrangement of microtubules.
o Give rise to basal bodies that direct the formation of cilia and
flagella.
o Also used to direct movement of material through the cell.
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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.
o Extremely thin protein fibers usually occurring in bundles.
o Similar in composition to the protein in the muscle (allows for
contraction).
o Associated with cell movement such as “Cyclosis”, cytoplasmic
streaming, amoeboid movement and “pinching off” during cell
division
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.
o Thin cylinders several times larger than
microfilaments.
o Each cylinder contains 13 rows of a globular
protein, tubulin, arranged in a spiral fashion.
o Found in both cytoplasm and certain organelles.
o Used to construct material to make up Cilia,
Flagella and Centrioles.
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.
o A colloidal substance, which can change from the gel (solid) to the sol (liquid) state with the
addition of heat or change in metabolic activity.
o Contains and supports all the cells organelles.
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2 Major Cell Metabolism Pathways:
o Protein synthesis & secretion
o Intracellular digestion
Sections of both types of ER can break free (blebbing) to produce small membrane bound sacs of either
proteins or lipids called vesicles. The vesicles move through the cytoplasm and join into another
membranous structure called the golgi apparatus. The golgi apparatus is similar looking to smooth ER at
first glance. The golgi apparatus prepares the contents of the vesicles for their storage or secretion from the
cell. Either way, new vesicles bleb off. Those destined for secretion move to the cell membrane and
exocytosis occurs. Those destined for future use in the cell become known as Lysosomes and contain
digestive hydrolytic enzymes used for hydrolysis of molecules in a cell. Lysosomes digest food particles that
they have taken in.
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