1. Genetics - Ch 10 Molecular Mechanisms of Gene Regulation

2. Control of Gene Expression DNA -------------> RNA ------------> protein transcriptional control translational control Operon: (prokaryotes) several adjacent genes regulated together and coding for proteins involved in a common process Operator: Repressor binding site Promoter: transcriptional activation site

3. Repressible Vs. Inducible Operons Repressible System: in biosynthetic (anabolic) pathways substrate present -> operon turned off Trp Operon Inducible System: in degradative (catabolic) pathways substrate present -> operon turned on Lac Operon

4. to metabolize (break down) lactose constitutiveinducible Z protein= ß-galactosidase a)cleaves lactose --> glu + gal b) shifts bonds in lactose --> allolactose

5. Lac Operon: Inducer always some repressors in cell allolactose is an inducer: makes repressor fall off operator transcription occurs

6. Lac Operon: Enhancer CRP protein: cAMP: cAMP receptor proteincyclic adenosine monophosphate CRP/cAMP: enhancer binds to activator site upstream from Promoter helps RNA pol to attach to Promoter low glucose --> high cAMP high glucose --> low cAMP

7. Lac Operon under Different Cell Conditions what if…? no glu, high lachigh cAMP, high allolachigh transcription high glu, no laclow cAMP, low allolac no transcription no glu, no lachigh cAMP, no allolacno transcription some glu & lac low cAMP, some allolac not enhanced, induced low transcription

8. Mutated Lac Operon & Areas what if …? I - no repressorLac operon turned on O c repressor can’t bindLac operon turned on to operator I s allolactose can’t bind Lac operon turned off to repressor I -d repressor can’t bindLac operon turned on to operator

9. Trp Operon for production of tryptophan a.a.

10. aporepessor (always present) combines with co-repressor (tryptophan) to form functional repressor [Trp] --> Trp operon turned off Trp Operon: Repressible System negative feedback loop

11. Trp Operon Controlled by Attenuation trpR P O 1 2 3 4 trpE trpD trp C trp B trpA attenuator Leader attenuation can form under certain conditions base-pairing can occur between 1 - 2 2 - 3 3 - 4 Attenuation

12. High levels of Tryptophan in Cell transcription & translation occur simultaneously in Prokaryotes leader transcript (1) has 2 trp codons (UGGUGG) ribosomes moves fast along transcript stem-loop 3 - 4 fprms, poly Us after early termination of transcription, translation stops (only leader peptide forms - has no function)

13. Low Levels of Tryptophan in Cell ribosome stalls at UGGUGG in leader transcript (1) stem-loop 2 - 3 forms, no poly U after transcription continues

14. Low Levels of other Amino Acids ribosome stalls way early stem-loops 1-2 & 3-4 form, poly U after early termination of transcription