1. Chapter 18 Bacterial Regulation of Gene Expression

2. 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

3. 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

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

5. 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

6. Inducible Operons
Absence of lactose vs. Presence of lactose

7. 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