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Viruses as Pathogens in Bacterial Gene Regulation

Viruses as Pathogens in Bacterial Gene Regulation. Bacterial DNA single double-stranded circular DNA densely supercoiled in a region called the nucleoid region replication occurs in both directions from the replication fork (no Okazaki) replication via binary fission (splitting)

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Viruses as Pathogens in Bacterial Gene Regulation

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  1. Viruses as Pathogens in Bacterial Gene Regulation • Bacterial DNA • single double-stranded circular DNA • densely supercoiled in a region called the nucleoid region • replication occurs in both directions from the replication fork (no Okazaki) • replication via binary fission (splitting) • asexual process • offspring are clones • very quick replication time ~20min • 1 E. coli can create a colony of 1 x108 in 12 hours

  2. Sources of Genetic Variation • mutations are the main source of variation (~9 million/day) • transformation • process by which bacteria pick up DNA from similar species and incorporate into their genome • in biotechnology E. coli can be induced into transduction with the addition of Ca+ to the growth medium • transduction • bacteriophage introduces new DNA into the bacteria

  3. Sources of Genetic Variation • conjugation • bacteria sex! • bacteria containing the F-factor (fertility) forms a pili • long extension that pulls another bacteria close • a cytoplasmic bridge is established and DNA is passed from the bacterium with the F factor (F+) to the recipient (F-) • F-factor may be located in a separate circular region called a plasmid • if the plasmid reinserts itself into the DNA is it called an episome • an episome is an example of a transposable element - a gene that can be relocated- • called transposons if they are larger segments • insertion segments are inverted repeats that act as boundaries that separate transposed genes • If the conjugation infers resistance to antibiotics it is renamed to R-factor (resistance)

  4. Lac Operon Concept • works by the process of feedback inhibition • product of the reaction blocks a step in the metabolic pathway leading to the product • shuts off the production at the DNA level - inhibits the production of mRNA • saves resources of the organism

  5. Operons • groups of enzymes that are grouped into the same mRNA transcript (ex: trp - gene for making tryptophan) • each protein has its own start and stop sequence • benefit: single on & off switch for entire process • switch is called the operator • located within the promoter region • can be switched off by the presence of a repressor bound to the operator • blocks attachment of the RNA Pol • product of a repressor gene that is some distance from the operon (trpR) • Repressors are reversible - only active if the corepressor is present to its ligand trp (allosteric inhibition)

  6. Inducible Repressor • the presence of an inducer inactivates repressor • ex: lactose • allolactose binds to the repressor changing its conformation • the repressor is released • suppression of enzyme for the uptake saves resources • negative control mechanism

  7. Positive Gene regulation • CAP promoter binds with cAMP stimulates the transcription in the absence of glucose (its preferred food) • called an activator

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