Chapter 18 Bacterial Regulation of Gene Expression

Response to Environment How can bacteria tune their metabolism to changing environments? Control occurs at 2 levels: 1. Cells can adjust activity of enzymes already present -sensitivity to chemical cues will increase or decrease activity (feedback inhibition) 2. Cells can adjust the amount made of certain enzymes -regulate expression of genes coding for enzymes

Operons Operator – segment of DNA positioned within or between promoter and enzyme coding genes that controls access to RNA polymerase Operon – cluster of genes with related functions ex: promoter, operator and genes they control for enzyme production

Operons Repressor- protein that reverses the action of operons - binds to operator and blocks attachment to RNA polymerase; prevents transcription of genes

Repressible and Inducible Operons Repressible operons – transcription is active but can be inhibited when a small molecule allosterically binds to protein EX: tryptophan to trp repressor Inducible operons – usually turned off but can be stimulated when a small molecule binds to regulatory protein EX: allolactose to lac repressor

Inducible Operons Absence of lactose vs. Presence of lactose

Positive Gene Regulation Occurs when a regulatory protein interacts directly with genome and switches transcription on. EX: CAP (catabolite activator protein) -activates transcription - on/off switch and volume control