Bacterial Genetics

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Bacterial Genetics

• Asexually reproducing (binary fission)
• High reproductive rates/short generation spans
• Variation in bacteria mainly caused by mutation
• Our variation mainly caused by recombination of
  existing alleles

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Sources
Although there is no meiosis, recombination of
alleles can occur

• Transformation (we will do a lab after exams)
• Transduction
• Conjugation

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Transduction

• Viruses may transfer (act as vector) DNA from one
  bacteria to another
• New bacterial DNA may line up with a homologous
  section of the bacterial chromosome and
  recombination (crossing over) may occur
• May be GENERALIZED TRANSDUCTION or SPECIALIZED
  TRANSDUCTION

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Generalized transduction

• Virus is in the lytic cycle
• Bacterial DNA that was degraded accidentally is
  incorporated into viral capsid
• Capsid injects bacterial DNA into new bacteria
• The genes transferred are random

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Specialized transduction

• Occurs from temperate viruses (in lysogenic
  cycle)
• Prophage comes out of bacterial chromosome and
  take adjacent genes with it
• Only specific genes are transferred in this way

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Conjugation

• Bacterial Sex
• Many bacteria have plasmids
• Small circular pieces of DNA separate from
  chromosome
• Contain only a few genes
• Not necessary to bacterias survival
• May give an advantage under certain environmental
  conditions

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F plasmids

• Have genes that allow bacteria to form sex pilli

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F plasmid

• Plasmids are transferred through the sex pilus
  during conjugation
• A copy of plasmid is first made then transferred
• F transfers to F-

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R plasmid

• Plasmid containing genes that make bacterial
  RESISTANT to antibiotics
• May have up to 10 antibiotic resistance genes on
  one plasmid
• Made possible by TRANSPOSONS

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Transformation

• Gets its name from Griffiths experiment with mice
• When bacteria take up foreign DNA from their
  surroundings
• Some bacteria do this naturally
• Some can be induced to do this (made competent
• Important in E. coli to take up plasmids that
  have been created to carry certain genes

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Anatomy of the lac operon
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The operator determines whether transcription
will occur by being able to bind with a
regulatory protein
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The regulatory gene codes for the regulatory
protein which is a repressor molecule
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Active repressor prevents transcription
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Effect of lactose on the lac operon
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Energy preference of E.coli
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The concentration of glucose is inversely
proportional to the concentration of cyclic AMP
Cyclic AMP binds with an activator protein and
helps RNA polymerase to bind to the promoter
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