1. Bacterial Physiology (Micr430) Lecture 13 Regulation of Gene Expression (Text Chapter: 6) (Moat book)

2. Cellular Regulations Regulation of metabolic pathways Regulation of gene expression

3. Regulation of metabolic pathways A cell has thousands of chemical reactions, if not regulated, chaos occurs Regulation of metabolic pathways is accomplished by adjusting rate of one or more regulatory enzymes that control the overall rate of the pathway Non-covalent binding between enzyme and pathway intermediate compounds Covalent modification of enzyme activity

4. Patterns of regulation Feedback inhibition – for a biosynthetic pathway, end product is usually a negative allosteric effector for a branch point enzyme. Simple feedback; for unbranched pathway Cumulative feedback; both effectors exert partial inhibition Concerted feedback; no inhibition unless both effectors bind Inhibition by isoenzymes

5. Patterns of feedback inhibition

6. Branched metabolic pathways

7. Patterns of regulation Positive regulation of a pathway By intermediate of a second pathway Precursor activation Regulatory enzymes usually control branch points of metabolic pathways and reactions are usually irreversible.

8. Enzyme kinetics Non-regulatory enzymes Michaelis-Menten equation v = V max * S/(K m + S) When S is small compared to K m, v is proportional to S -> v = V max * S/K m When S is much larger than K m, then v ~ V max

9. Michaelis-Menten kinetics

10. Enzyme kinetics Regulatory enzymes follow sigmoidal curve. Binding of one substrate molecule increases the affinity of the enzyme for a second substrate molecule or increases rate of product formation from site already occupied – positive cooperactivity.

11. Regulatory Enzymes

12. Enzyme kinetics Conformational changes in regulatory enzymes

13. Regulation by covalent modification

14. Gene expression regulation Definitions Structural gene Promoter Operator Operon and polycistronic Regulatory gene Inducible Repressible

15. Gene expression regulation Negative control: regulatory proteins bind to operator region to prevent transcription Positive control: regulatory proteins bind to region near promoter to increase transcription Regulation at transcriptional level relies heavily on DNA binding proteins

18. The lac Operon Responsible for utilization of lactose as a carbon source  -galactosidase, encoded by lacZ, cleaves  -1,4-linkage of lactose Permease (encoded by lacY) allows entrance of lactose lacA encodes a thiogalactoside transacetylase, whose cellular role is not known.