Regulation of Gene Transcription Chapter 13 Regulation of Gene Transcription

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.

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

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

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

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

b-galactosidase = product of lacZ gene

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

Negative Regulation of lac Operon

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

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