Division Ave. High School AP Biology

Transcription

1 Control of Prokaryotic (Bacterial) Genes Bacterial metabolism n Bacteria need to respond quickly to changes in their environment u if they have enough of a product, need to stop production n why? waste of energy to produce more STOP n how? stop production of enzymes for synthesis u if they find new food/energy source, need to utilize it quickly n why? metabolism, growth, reproduction GO n how? start production of enzymes for digestion Remember Regulating Metabolism? n Feedback inhibition u product acts as an allosteric inhibitor of 1 st enzyme in tryptophan pathway = inhibition u but this is wasteful production of enzymes Oh, I remember this from our Metabolism Unit! 1

2 Different way to Regulate Metabolism n Gene regulation u instead of blocking enzyme function, block transcription of genes for all enzymes in tryptophan pathway n saves energy by not wasting it on unnecessary protein synthesis Now, that s a good idea from a lowly bacterium! = inhibition Gene regulation in bacteria n Cells vary amount of specific enzymes by regulating gene transcription u turn genes on or turn genes off n turn genes OFF example if bacterium has enough tryptophan then it STOP doesn t need to make enzymes used to build tryptophan n turn genes ON example if bacterium encounters new sugar (energy GO source), like tose, then it needs to start making enzymes used to digest tose Bacteria group genes together n Operon u genes grouped together with related functions n example: all enzymes in a metabolic pathway u = binding site n single controls transcription of all genes in operon n transcribed as one unit & a single m is made u = binding site of repressor protein 2

3 So how can these genes be turned off? n Repressor protein u binds to at site u blocking u blocks transcription Operon model Operon:, & genes they control serve as a model for gene regulation TATA repressor m gene1 gene2 gene3 gene4 Repressor protein turns off gene by blocking binding site. repressor = repressor protein Repressible operon: tryptophan TATA repressor m Synthesis pathway model When excess tryptophan is present, it binds to tryp repressor protein & triggers repressor to bind to u blocks (represses) transcription gene1 gene2 gene3 gene4 repressor repressor protein tryptophan conformational change in repressor protein! repressor tryptophan repressor protein complex 3

4 Tryptophan operon What happens when tryptophan is present? Don t need to make tryptophanbuilding enzymes Tryptophan is allosteric regulator of repressor protein Inducible operon: tose TATA repressor gene1 gene2 gene3 gene4 m Digestive pathway model When tose is present, binds to repressor protein & triggers repressor to release u induces transcription repressor repressor protein conformational change in repressor protein! repressor tose tose repressor protein complex Lactose operon What happens when tose is present? Need to make tosedigesting enzymes Lactose is allosteric regulator of repressor protein 4

5 Jacob & Monod: Operon n Francois Jacob & Jacques Monod u first to describe operon system u coined the phrase operon Jacques Monod Francois Jacob Operon summary n Repressible operon u usually functions in anabolic pathways n synthesizing end products u when end product is present in excess, cell allocates resources to other uses n Inducible operon u usually functions in catabolic pathways, n digesting nutrients to simpler molecules u produce enzymes only when nutrient is available n cell avoids making proteins that have nothing to do, cell allocates resources to other uses 5