All metabolic systems are catalyzed by enzymes

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Regulation of Bacterial Gene Expression

• All metabolic systems are catalyzed by enzymes
• Feedback inhibition
• Turns off functioning enzymes
• Stops cell from performing unneeded reactions
• Constitutive enzymes
• Repressible enzymes
• Inducible enzymes

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RepressionInhibits gene expression and
decreases synthesis of enzymes Usually in
response to build up of product Mediated by
regulatory proteins called repressors which block
RNA polymerase activity
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Operon Model of Gene ExpressionBased on studies
of induction of the enzymes of lactose catabolism
on E. coli
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Mutations

• Change in the genetic material
• Changes in the genotype
• may or may not cause phenotypic changes
• Changes may be neutral, beneficial, or harmful
• May be repaired through nucleotide excision
• Mutagen
• Agent that causes mutations
• Spontaneous mutations
• Occur in the absence of a mutagen

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Types of Mutations

• Base substitution (point mutation)
• Missense mutation

• Change in one base
• Result in change in amino acid

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• Nonsense mutation

• Results in a nonsense codon

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Mutation

• Insertion or deletion of one or more bases
• Alter all base pairs after this point

• Frameshift mutation

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Genetic Recombination

• Exchange of genes between two DNA molecules to
  form new combinations on genes on a chromosome
• Along with mutations, contributes to genetic
  diversity

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Types of Genetic Transfer

• Vertical gene transfer
• Horizontal gene transfer

• Occurs during reproduction, between generations
  of cells
• Transfer of genes between cells of the same
  generation

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Horizontal gene transfers

• Transformation
• Transduction
• Conjugation
• All result in recombination
• Combining genes from two different cells

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Transformation
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Transduction
Phage protein coat
Bacterial chromosome
Recombinant
Phage DNA and proteins are made, and the
bacterial chromosome is broken down into pieces.
A phage infects the donor bacterial cell.
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Bacterial DNA
Donor bacterial DNA
Recipient bacterial DNA
Phage DNA
Recipient cell
Recombinant cell
Occasionally during phage assembly, pieces of
bacterial DNA are packaged in a phage capsid.
Then the donor cell lyses and releases phage
particles containing bacterial DNA.
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A phage carrying bacterial DNA infects a new host
cell, the recipient cell.
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Recombinant can occur, producing a recombinant
cell with a genotype different from both the
donor and recipient cells.
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Conjugation
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Conjugation
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Plasmids

• Conjugative plasmid Carries genes for sex pili
  and transfer of the plasmid
• Dissimilation plasmids Encode enzymes
  for catabolism of unusual compounds
• R factors Encode antibiotic resistance

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Plasmids
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Transposons

• Segments of DNA that can move from one region of
  DNA to another
• Contain insertion sequences for cutting and
  resealing DNA (transposase)
• Complex transposons carry other genes