Prokaryotic Gene Expression II Bacteria

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Prokaryotic Gene Expression IIBacteria
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Overall outline

• Introduction to Bacteria
• Genetic Recombination in Bacteria
• Regulation of Transcription

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Introduction to Bacteria

• Bacterial structure
• Bacterial life cycle
• E. coli DNA
• E. Coli dividing binary fission
• Plasmids
• Replication of the bacterial chromosome

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Bacterial structure

• Prokaryotes are distinguished by having no
  membrane-bound organelles.
• The DNA genome is gathered in a central region
  called the nucleoid.
• Bacteria are also uniquely characterized by a
  rigid cell wall which serves to resist osmotic
  stress.
• Bacteria can be classified in terms of their
  cell-wall components and in terms of their shape.

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Bacterial life cycle

• Bacterial growth (generally exponential) usually
  involves asexual reproduction (binary fission)
  sexual reproduction via gene transfer is rarer.
• The resulting semi-log growth curve involves
  lag, logarithmic and stationary phases.

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E. coli DNA
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E. Coli dividing binary fission
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Plasmids
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Replication of the bacterial chromosome
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Genetic Recombination in Bacteria

• Detecting genetic recombination in bacteria
• Transduction
• Conjugation Bacterial mating
• Recombination in E. coli
• Insertion sequences, the simplest transposons
• Insertion of a transposon and creation of direct
  repeats
• Anatomy of a composite transposon

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Detecting genetic recombination in bacteria
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Transduction
(during lysogeny)
(during lysis)
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Conjugation Bacterial mating
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Recombination in E. coli
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Recombination in E. coli
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Insertion sequences, the simplest transposons
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Insertion of a transposon and creation of direct
repeats
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Anatomy of a composite transposon
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Regulation of Transcription

• Regulation of a metabolic pathway
• The lac operon regulated synthesis of inducible
  enzymes
• cAMP
• Positive control cAMP receptor protein
• The trp operon regulated synthesis of
  repressible enzymes

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Regulation of a metabolic pathway
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The lac operon regulated synthesis of inducible
enzymes

• Regulation of gene expression often occurs at
  the level of transcription.
• The most common strategy is to control the
  binding of RNA polymerase to the promoter or to
  block its precessive activity along the operon.
• Eukaryotic regulatory mechanisms are more
  complicated and involve a variety of DNA enhancer
  elements and protein transcription factors.
• The lac operon depicted here is a prototypical
  system.

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cAMP
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Positive control cAMP receptor protein
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The trp operon regulated synthesis of
repressible enzymes