ch. 14: regulation of cellular processes (memorize)

when can bacterial cells regulate gene expression

transcription, translation, and protein activity

what are constitutive genes

genes that are always on, producing a constant supply of proteins, like enzymes in central metabolism

what are inducible genes

genes that are usually off but can be turned on in response to a signal or environmental condition, like the lac operon when lactose is present

what are repressible genes

genes that are usually on but can be turned off when their product is not needed, like amino acid biosynthesis enzymes

what is negative transcriptional control

a repressor protein binds DNA to block RNA polymerase and prevent transcription

what is positive transcriptional control

an activator protein binds DNA to help RNA pollymerase bind and increase transcription

how do inducers affect repressors

inducers bind repressors and change their shape so they cannot block transcription, turning genes on

how do inducers affect activators

inducers or ligands bind activators to allow them to help RNA polymerase, increasing transcription

in the lac operon, what is the repressor’s role

lacl binds the operator and blocks transcription when lactose is absent

in the lac operon, what is allolactose’s role

allolactose is an inducer that binds Lacl and prevents it from blocking transcription

in the lac operon, what is CAP’s role

CAP binds upstream of the promoter when cAMP is present, helping RNA polymerase start transcription efficiently when glucose is absent

what happens in diauxic growth

bacteria use glucose first, then lactose; glucose blocks lactose entry (inducer exclusion) and turns off lactose genes (catabolite repression)

what is a two-component signal transduction system

a sensor kinase detects an external signal, phosphorylates itself, then transfers the phosphate to a response regulator that changes transcription

how is a phosphorelay system different from a two-component system

a phosphorelay involves multiple phosphorylation steps, adding more control points before the response regulator changes gene expression

how do alternate sigma factors help bacteria

different sigma factors direct RNA polymerase to specific promoters, turning on distinct sets of genes in response to environmental changes (like heat shock, starvation, or flagella formation)

how do CAP, cAMP, and the lac repressor work together to regulate the lac operon

• lac repressor: blocks transcription when lactose is absent

• allolactose: inactivates repressor when lactose is present

• CAP + cAMP: increase transcription when glucose is absent

what is quorum sensing

bacteria detect population density through chemical signals; when enough signals accumulate, they turn on genes for biofilms or virulence factors