PR PROK CELL.docx - Bioenviroclasswiki

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12 Δεκ 2012 (πριν από 4 χρόνια και 9 μήνες)

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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









http://videos.howstuffworks.com/hsw/10309
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prokaryotic cells video






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Differences between prokaryotic and Eukaryotic
cell


Prokaryotic cells

Eukaryotic cells

Small cells
<5micrometers

Large cells >10
micrometers


Always unicellular

Often multicellular

No nucleus, membrane
bound organelles like
mitochondrion

Always have nucleus and
membrane bound
organelles

DNA is circular,

without
proteins

DNA is linear, associated
with proteins to form
chromatin

Ribosomes are s
mall (70S)

Ribosomes are large (80S)

No cytoskeleton

Always has cytoskeleton

Motility by rigid rotating
flagellum made of flagellin

Motility by flexible waving
cilia or flagellae made of
tubulin.

Cell division by binary
fission

Cell division by mitosis
or
meiosis

Reproduction is always
asexual

Reproduction is asexual or
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 surf
ace. 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
mat
erial 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
protein
s 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 FISS
ION

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.

Decompositio
n

Making of yoghurt, tea







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