2. AP Biology 2007-2008 Control of Prokaryotic (Bacterial) Genes

3. AP Biology Bacterial metabolism Bacteria need to respond quickly to changes in their environment  if they have enough of a product, need to stop production _____waste of energy to produce more _____stop production of enzymes for synthesis  if they find new food/energy source, need to utilize it quickly _____metabolism, growth, reproduction _____start production of enzymes for digestion STOP GO

4. AP Biology Different way to Regulate Metabolism Gene regulation  instead of blocking enzyme function, block transcription of genes for all enzymes in tryptophan pathway saves energy by not wasting it on unnecessary protein synthesis = inhibition - Now, that’s a good idea from a lowly bacterium! - -

5. AP Biology Gene regulation in bacteria Cells vary amount of specific enzymes by ____________________________ turn _________or turn ___________ _______________________________ if bacterium has enough tryptophan then it doesn’t need to make enzymes used to build tryptophan __________________________________ if bacterium encounters new sugar (energy source), like lactose, then it needs to start making enzymes used to digest lactose STOP GO

6. AP Biology Bacteria group genes together __________  genes grouped together with related functions example: all enzymes in a metabolic pathway  __________= RNA polymerase binding site single promoter controls transcription of all genes in operon transcribed as one unit & a single mRNA is made  _________= DNA binding site of________________

7. AP Biology So how can these genes be turned off?  ______________________ binds to DNA at operator site  blocking RNA polymerase  blocks transcription

8. AP Biology operatorpromoter Operon model DNATATA RNA polymerase repressor = repressor protein ___________ ___________________________________ serve as a model for gene regulation gene1gene2gene3gene4 RNA polymerase ___________________turns off gene by blocking RNA polymerase binding site. 1234 mRNA enzyme1enzyme2enzyme3enzyme4

9. AP Biology mRNA enzyme1enzyme2enzyme3enzyme4 operatorpromoter Repressible operon: tryptophan DNATATA RNA polymerase tryptophan repressor repressor protein repressor tryptophan – repressor protein complex ______________________________ When excess tryptophan is present, it binds to ____________________& triggers repressor to bind to DNA  blocks (represses) transcription gene1gene2gene3gene4 conformational change in repressor protein! 1234 repressor trp RNA polymerase trp

10. AP Biology Tryptophan operon What happens when tryptophan is present? _________________________________________ Tryptophan is allosteric regulator of repressor protein

11. AP Biology mRNA enzyme1enzyme2enzyme3enzyme4 operatorpromoter Inducible operon: lactose DNATATA RNA polymerase repressor repressor protein repressor lactose – repressor protein complex lactose lac repressor gene1gene2gene3gene4 ___________________________ When lactose is present, binds to ___________________________& triggers repressor to release DNA  induces transcription RNA polymerase 1234 lac conformational change in repressor protein! lac

12. AP Biology Lactose operon What happens when lactose is present? _______________________________________ Lactose is allosteric regulator of repressor protein

13. AP Biology Jacob & Monod: lac Operon Francois Jacob & Jacques Monod  first to describe operon system  coined the phrase “operon” 1961 | 1965 Francois JacobJacques Monod

14. AP Biology Operon summary ____________________  usually functions in ___________pathways ______________end products  when end product is present in excess, cell allocates resources to other uses  ____________________  usually functions in_____________ pathways, _____________ nutrients to simpler molecules  produce enzymes only when nutrient is available cell avoids making proteins that have nothing to do, cell allocates resources to other uses

15. AP Biology 2007-2008 Don’t be repressed! How can I induce you to ask Questions?