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 x10 8 in 12 hours

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

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)

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

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)

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

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