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Bacteria

Sunday, 22 June 2014

10:51 AM

Describe the structure of a bacterial chromosome including the arrangement of DNA within bacterial cells
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(Knowledge of Hfr is not required
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The bacterial DNA attaches itself to the mesosome, a highly folded region of the cell membrane
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2
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This
process is assisted by DNA gyrase which removes the positive supercoiling
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3
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The bacteria chromosome s separate and the cell membrane invaginates
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Transformation
Transformation is the uptake by the cell of a DNA molecule from the surrounding environment and the incorporation of
this molecule into the recipient chromosome an a heritable form
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This is due to errors
made during the viral lifecycle
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Generalised transduction
1
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2
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3
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 Because any random DNA fragment maybe packaged into the viral particle, any segment of the
bacterial DNA may be transferred this way
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During the phage lysogenic phase, the phage's DNA is integrated into a very specific area in the host's
chromosome
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When the viral DNA excises itself during the lytic phase, some bacterial DNA that is next to the viral
integration site is excised along with it
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When the resulting virus infects another cell, it will pass the bacterial DNA into the cell along with its own
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 Because the viral DNA integrates at a specific location, when it excises, the bacterial DNA removed will
be those near to the prophage
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Conjugation
Conjugation involves the direct transfer of DNA between 2 bacterial cells that are in contact
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Bacterial cells that have the
F plasmid act as donors and those without act as recipients
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The F plasmid mostly codes
for the production of the sex pili, which acts as a grappling hook to pull two cell together
1
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In the donor cell the F factor is nicked at the origin of transfer, resulting in the separation of one strand of
DNA from the other intact circular stand
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3
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4
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The remaining strand in the
donor cell also synthesises its own complementary strand
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• A structural gene is a region of DNA that codes for a protein or RNA molecule that forms part of a structure or has
an enzymatic function (e
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lacY, lacZ, lacA, but excludes lacI)
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g
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Distinguish between the concept of repressible and inducible systems of gene regulation using trp and lac operon as
examples respectively (attenuation of trp operon is not required)
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g
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If abundance
continues, the cell can stop synthesizing additional gene by blocking transcription of the trp operon
 Negative control
○ Consists of a promoter, an operator and 5 genes encoding the enzymes catalyzing the last steps of
tryptophan synthesis
○ Regulatory gene trpR codes for a repressor protein

At normal conditions, tryptophan concentrations are low:
• The repressor protein is inactive and not bound to the operator region
• The promoter remains available to RNA polymerase for transcription
• E
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g
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• The lac operon is a cluster of structural genes that specify enzymes taking part in metabolism of lactose
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The activity of these regions is
in turn determined by a repressor molecules specified by a separate regulator gene

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