1. Regulation of Gene Transcription
Chapter 13
Regulation of Gene Transcription

2. Prokaryotic Gene Regulation
Sugar Utilization
Glucose is the preferred carbon source.
Glucose goes directly into glycolysis pathway.
Other sugars must be converted into glucose before it can enter glycolysis pathway.
Advantageous to have potential to use other sugars (e.g., lactose and arabinose)
Regulate transcription of genes that code for proteins necessary for utilization of these other sugars.

3. Transcription regulated by proteins that bind to DNA
Promoter = binding site for RNA polymerase

4. Activator bound to operator facilitates transcription
Repressor bound to operator blocks transcription

5. Allosteric regulation of activators & repressors
Effector binding changes conformation of DNA binding site
Activator + Effector Binds to DNA
Repressor + Effector Does not bind to DNA

6. Operon = group of genes that are coordinately regulated
Lac Operon
Operon = group of genes that are coordinately regulated
(+ regulatory DNA)
3 structural genes
lac I
constitutively transcribed
multigenic mRNA
AUG
AUG
stop
AUG
stop
stop
Inducer = Effector that binds to Repressor
Transports lactose into cell

7. b-galactosidase = product of lacZ gene

8. Induction = Relief of repression
Promoter Operator
Inducer
Induction = Relief of repression

9. Negative Regulation of lac Operon

10. Catabolite Repression
Positive Regulation
Controls all operons that code for proteins needed for metabolism of sugars other than glucose --- Only allows their transcription when glucose is absent.
Adenylate cyclase
Glucose inhibits activity of adenylate cyclase
ATP
cAMP
CAP = Catabolite Activator Protein
Helps RNA polymerase bind to promoter

11. Lactose Glucose Transcription state of lac operon
Low High Not transcribed
High High Transcribed at low levels
Low Low Transcribed at low levels
High Low Transcribed at high levels