PROKARYOTIC CELL
STRUCTURE OF E.coli
2.2.1 Draw and label a diagram of the ultrastructure of
Escherichia coli (E.coli) as an example of a prokaryote
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prokaryotic cells video
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Differences between prokaryotic and Eukaryotic
cell
Prokaryotic cells
Small cells<5micrometers
Eukaryotic cells
Large cells >10
micrometers
Always unicellular
No nucleus, membrane
bound organelles like
mitochondrion
DNA is circular, without
proteins
Often multicellular
Always have nucleus and
membrane bound
organelles
DNA is linear, associated
with proteins to form
chromatin
Ribosomes are small (70S) Ribosomes are large (80S)
No cytoskeleton
Always has cytoskeleton
Motility by rigid rotating
Motility by flexible waving
flagellum made of flagellin cilia or flagellae made of
tubulin.
Cell division by binary
Cell division by mitosis or
fission
meiosis
Reproduction is always
Reproduction is asexual or
asexual
sexual
Functions of parts of a prokaryotic cell
Cell wall: Outside the plasma membrane of most
prokaryotes is present fairly rigid, chemically complex
cell wall. Functions: The wall protects the cell and helps
maintain its shape. It prevents damage from outside
and also bursting if internal pressure is high. In some
prokaryotes, another layer, a sticky coat called a
capsule surrounds the cell wall and further protects the
cell surface. Capsules help glue prokaryotes to surfaces,
specific host tissues, such as the surface of a tooth or the
lining of small intestine. They are polysaccharide
coatings.
Plasma membrane: Controls entry and exit of
substances, pumping some of them in by active
transport.
Cytoplasm: Contains enzymes that catalyse the
chemical reactions of metabolism and contains DNA in
a region called the nucleoid.
Pili: pili are proteins that project outward from the
bacterial wall . Pili are used to exchange genetic
material between bacterial cells.
Flagella: Solid protein structures, with a corkscrew
shape, projecting from the cell wall, which rotate and
cause locomotion (propel the prokaryotic cell through
its liquid environment.)
Nucleoid: The region of the cytoplasm that contains
naked DNA, which is the genetic information of the cell.
The nucleoid is not separated from the rest of the
cytoplasm by a membrane.
Plasmid: Most prokaryotes contain small loops of DNA
outside the nucleoid.
Some disease causing bacteria possess plasmids that
allow them to inactivate antibiotics making them much
more difficult to kill. Used in genetic engineering and
contains genes resistance to antibiotics.
Ribosomes: Structures composed of combination of
proteins and RNA. Ribosomes are small granular
structures that synthesise proteins by translating
messenger RNA. Some proteins stay in the cell and
others are secreted.
2.2.3 Identify structures from 2.2.1 in electron
micrographs of E.coli.
BINARY FISSION
2.2.4 State that prokaryotic cells divide by binary
fission.
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Prokaryotic cells divide by binary fission.
This is an asexual method of reproduction in which the
cell divides into two equal sized cells.
The cells are genetically identical.
During this process, the DNA is copied, the two
daughter chromosomes become attached to different
regions on the plasma membrane, and the cell divides
into two genetically identical daughter cells.
What is a disadvantage of the prokaryotic cells having
their DNA free in the cytoplasm without a nuclear
membrane?
The DNA is more vulnerable to the life functions of the
cell. These cell functions require enzymes and raw
materials, and produce products that may potentially
damage the DNA. This creates a greater chance of
interactions and mutations or harmful changes.
What structures are involved in sexual reproduction in
prokaryotic cells?
Pili are plasma membrane extensions that serve to allow
joining of bacterial cells so that exchange of DNA
between cells may occur, thus bringing about sexual
reproduction.
Examples of prokaryotic cells are bacteria and blue
green algae (cyanobacteria)
Functions:
Nitrogen fixation.
Photosynthesis (bacteria contain bacterio chlorophyll)
Anaerobic respiration.
Fermentation.
Decomposition
Making of yoghurt, tea
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