bacterial genetics.ppt
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Genetics of Bacteria
• Bacterial genome =
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Genetics of Bacteria
• Bacterial genome = One circular DNA molecule
• E. coli chromosome has 100 times more Dna than in a typical virus, but much less than a eukaryotic cell.
• Packed into nucleoid region of cell
• Plasmid =
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Genetics of Bacteria
• Bacterial genome = One circular DNA molecule
• E. coli chromosome has 100 times more Dna than in a typical virus, but much less than a eukaryotic cell.
• Packed into nucleoid region of cell• Plasmid = small circular extra piece of
DNA
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Bacterial Genetic Recombination
• What is the main source of genetic recombination in bacteria?
• Mutations
• What are the other sources of recombination?
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Transformation
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Transduction
What is the vector of
transduction?
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Conjugation
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Plasmids• What is a plasmid?• Small circular, self replicating piece of
bacterial DNA• Episomes = plasmids that can reversibly
incorporate into the bacterial chromosome
• Plasmid genes are advantageous to the bacteria that has them
• Plasmids that confer resistance to antibiotics are called R plasmids
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Transposons
• Jumping genes
• Does not depend on complementary base pairing between homologous regions of the chromosome.
• Transposons move to regions that the gene has never been
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Transposase recognizes the inverted repeats
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Targeted inverted
repeats are cut, and the target is cut, then the transposon is
inserted
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Composite transposons move extra genes along with the inserted sequence,
and are very beneficial to the bacteria
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Regulation of Gene Expression
Regulatory gene = codes for regulatory protein
Regulatory protein = binds to the operator and stops transcription of the structural geneOperator = on /off switch for transcription of structural gene
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Repressible operons• Repressible operons have structural genes
that code for the production of the substrate.
• The repressor protein is produced in an inactive form, leaving the operator open
• In the presence of the substrate, the substrate will allosterically bind to the repressor protein (is a co-repressor) and activate the repressor protein causing it to bind to the operator
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Inducible operons• Inducible operons have sturcutral genes
that produce enzymes that break down the substrate.
• The repressor is translated into its active configuration and will bind to the operator in the absence of the substrate.
• If the substrate is present, it binds to the repressor protein and de-activates it, thereby opening up the operator.
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Feedback control
As the lactose is degraded by the new enzymes, the regulatory protein once again binds to the operator
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