1. Control of Gene Expression
If all cells have the same genome, why are they so different from each other?

2. Two levels of metabolic control
Feedback inhibition – quick response to short term fluctuations in amount of required substance
Operon model – genes switched on or off by changes in the cell

3. Jacob and Monod’s Operon Model – cluster of genes under the control of a promoter - genes are either expressed together or not at all

4. Components of an operon
Promoter – sequence recognized by RNA polymerase
Operator – segment of DNA to which a regulator binds
Structural genes – genes regulated by the operon
Regulatory genes – code for regulatory proteins

5. Operon control Regulates the expression of genes depending on environmental conditions
Negative gene regulation
repressor binds to operator preventing transcription
Repressible
transcription usually on but can be inhibited by presence of product
trp operon
Inducible
transcription usually off but can be stimulated by presence of substrate
Positive gene regulation
activator protein binds to DNA at a site other than the operator allowing transcription to occur

6. trp operon repressible gene regulation

7. lac operon inducible gene regulation

8. lac operon positive gene regulation CRP-cAMP or CAP is an activator

10. Differential gene expression in eukaryotes
Regulation of chromatin structure
Regulation of transcription initiation
Enhancers (control DNA sequence)
Activators
Repressors
3. Post-transcriptional regulation
RNA processing
mRNA degradation
Initiation of translation
Protein processing and degradation