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Control mechanisms

Control mechanisms. 5.5. Controlling Transcription and Translation of Genes. Housekeeping Genes : needed at all times: needed for life functions vital to an organism. Constantly transcribed and translated. not all proteins are needed at all times

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Control mechanisms

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  1. Control mechanisms 5.5

  2. Controlling Transcription and Translation of Genes • Housekeeping Genes: needed at all times: needed for life functions vital to an organism. • Constantly transcribed and translated. • not all proteins are needed at all times • Ex// insulin only need when glucose levels are high • Transcription factors: proteins that switch on genes by binding to DNA and helping the RNA polymerase to bind. • Gene Regulation: turning on or off specific genes depending on requirements of organism. • Vital to survival.

  3. Control of Gene Expression in Eukaryotic Cells

  4. Operons Operon: cluster of genes under control of a promoter and operator (prokaryotic). Acts as a simple regulatory loop.

  5. Repressor Protein: regulatory molecule that binds to an operator site and prevents the transcription of an operon.

  6. Two Major Operons (in E. Coli) • lacoperon • Required for transport and metabolism of lactose • trpoperon • Codes for the production of tryptophan  an amino acid.

  7. lacoperon (1) • Lactose: ____________ + ______________ • E. Coli bacteria found in mammalian intestines can use energy from lactose for growth. • β-galactosidase: enzyme that catalyzes lactose. • When lactose not available, B-g is not made. • When would B-g cease on being produced by E. Coli in a mammalian intestine? ______________________________________________

  8. lacoperon (2) • Consists of three genes: • lacZ: gene for the enzyme β-g. • LacY: gene for β-g Permease: allows lactose to be permeable to cell membrane. • lacA: unknown function.

  9. lacoperon: If Lactose not Present • Lacl protein: repressor protein of lactose metabolism • Binds to the lacoperon operator, preventing RNA polymerase from transcribing the lacoperon genes. • Operon and operator actually overlap, so RNA poly cannot bind to DNA.

  10. lacoperon: If lactose IS present • If lactose present, lacl must be removed from operator so lacoperon genes can be transcribed. • Lactose: known as an ‘inducer.’ Binds to LacI protein  change conformation of LacI  cannot stay bound to operator region  no more block!

  11. trpoperon(1) • Tryptophan: an _______________ used by E.Coli to make ________________. • E. Coli in inside of mammalian intestine can absorb trp from diet. If no host, needs to produce trp. • 5 genes responsible in the metabolic pathway of the trpoperon.

  12. Trpoperon: when trp is not present • Inactive repressor is not blocking operator. • RNA polymerase can transcribe operon.

  13. Trpoperon: when trp is present • Tryptophan acts as a corepresser: binds to the repressor protein  conformation change  can bind to the operator  block transcription. (NO NEED FOR ENZYMES THAT MAKE TRP WHEN TRP IS ALREADY PRESENT!)

  14. http://www.youtube.com/watch?v=oBwtxdI1zvk

  15. Seatwork/Homework • Page258, #1-6.

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