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Genetics - Ch 10
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  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. Lac Operon to metabolize (break down) lactose constitutive inducible Z protein= ß-galactosidase 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 protein cyclic 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 lac high cAMP, high allolac high transcription high glu, no lac low cAMP, low allolac no transcription no glu, no lac high cAMP, no allolac no transcription low cAMP, some allolac not enhanced, induced low transcription some glu & lac

  8. Mutated Lac Operon & Areas what if …? I- no repressor Lac operon turned on Oc repressor can’t bind Lac operon turned on to operator I-d repressor can’t bind Lac operon turned on to operator Is allolactose can’t bind Lac operon turned off to repressor

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

  10. Trp Operon: Repressible System [Trp] --> Trp operon turned off aporepessor(always present) combines with co-repressor(tryptophan) to form functional repressor 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 • attenuation can form • under certain conditions • base-pairing can occur • between • 1 - 2 2 - 3 3 - 4

  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