Regulation of Gene Expression Prokaryotes

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Regulation of Gene ExpressionProkaryotes
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I. Genetics of Bacteria

• A. Bacteria are prokaryotes meaning they do NOT
  have a nucleus
• B. Instead they have 1 tightly condensed
  double-stranded DNA circular chromosome called a
  nucleoid.
• C. During replication DNA is copied in both
  directions at a single point of origin

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II. Bacteria Reproduction

• A. Bacteria can reproduce several ways although
  the most common is asexual binary fission. Where
  all genes are identical with a few mutations
  every 1,000 replications which can result in
  significant variations.

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II. Bacteria Reproduction

• B. Bacteria can also reproduce through
  conjugation a primitive method of sexual
  reproduction.
• 1. With the use of a plasmid which allows the
  bacteria to create a pillis, or bridge between
  two different bacteria that allows for DNA
  exchange. (F plasmid)

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• C. Plasmids are foreign, small circular,
  self-replication DNA molecules that are found
  within bacteria.
• 1. other plasmids include the R plasmid which
  allows for bacteria to be resistant to
  antibiotics
• D. Other variation due to
• Transformation
• Transduction

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III. Gene Expression

• A. In eukaryotes to go from DNA to a protein the
  steps are compartmentalized due to the nuclear
  envelope in prokaryotes gene expression happens
  all together.

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IV. Gene Regulation

• A. In prokaryotes gene regulation is controlled
  by operons. An operon is a set of genes and the
  switches that control the expression of those
  genes.
• B. There are 2 main types of operons
• 1. Repressible (tryptophan operon)
• 2. Inducible (lac operon)

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1. Trp Operon Repressible always turned on
unless repressor is activated

• a. Consists of a promoter and 5 adjacent
  structural genes that code for the 5 separate
  enzymes necessary to synthesize the amino acid
  tryptophan.
• b. RNA polymerase binds to the operator along the
  promoter creating one long strand of mRNA.
• c. Trp operon is only turned off when the
  repressor, activated by the corepressor trp,
  binds to the operator does transcription stop.
  (Recall what this is called from previous
  chapters, enzyme changes shape)

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2. Lac operon Inducible always turned off but
can be stimulated or induced

• a. In order for E. coli to utilize lactose as an
  energy source they need 3 enzymes to break the
  disaccharide which are coded in the lac operon.
• b. In order for this to happen the repressor must
  be removed from the operator and RNA must bind to
  the promoter region.
• c. Allolactose, isomer of lactose, is the inducer
  that binds to the active repressor inactivating
  it.

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• Repressible anabolic pathways
• Only when sufficient end product is there
• Inducible catabolic pathways
• Only active when product is available

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V. Positive Gene Regulation

• A. When both glucose and lactose are both present
  E. coli prefers using glucose but when glucose
  is in low supply and lactose is high enzymes are
  created to allow for this breakdown.
• B. When glucose is in low supply cyclic AMP
  (cAMP) accumulates. This molecule can bind to a
  regulatory protein called catabolite activator
  protein (CAP).
• C. When cAMP binds with CAP it can attach to the
  lac operon at the promotor (increase affinity of
  RNA polymerase)to stimulate transcription.

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