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Regulation of Gene Expression

Regulation of Gene Expression. Operons. Operon System (bacteria). Structural gene Operon Polycistronic mRNA Operator Regulator gene Repressor. Overview animation. Operon Structure. PROMOTER---OPERATOR----gene 1—gene 2—gene 3 “Regulator gene” (located elsewhere on chromosome).

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Regulation of Gene Expression

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  1. Regulation of Gene Expression Operons

  2. Operon System (bacteria) • Structural gene • Operon • Polycistronic mRNA • Operator • Regulator gene • Repressor • Overview animation

  3. Operon Structure PROMOTER---OPERATOR----gene 1—gene 2—gene 3 “Regulator gene” (located elsewhere on chromosome)

  4. Negative controlshutting something down

  5. Inducible Operons Normally OFF, induced (turned on) only when needed Ex. Lac operon (3 enzymes for catabolism of lactose) • repressor binds at operator : no transcription • lactose binds repressor, comes OFF operator : Transcription can proceed!

  6. This is the graphic from your textbook. I like the one on the next slide better

  7. The lac operon: inducible operon

  8. The lac operon: inducible operon Inducible operon animation (lac operon)

  9. Repressible Operons Normally ON, repressed (turned off) when not needed Example: Genes for amino acid biosynthetic enzymes Arginineoperon and tryptophan operon are examples. • Operon is actively transcribing • Arginine (or tryptophan) is synthesized • If arginine (or tryptophan) accumulates beyond useful levels, arg (trp) acts as COREPRESSOR • Corepressor + repressor protein bind to operator, SHUT OFF OPERON

  10. This is the graphic from your textbook. I like the one on the next slide better

  11. The trp operon: repressible operon

  12. The trp operon: repressible operon

  13. The trp operon: regulated synthesis of repressible enzymes Repressible operon animation (trp operon)

  14. Positive controlramping something up

  15. Activator protein instead of a repressor. • The activator protein promotes the binding of RNA Polymerase to the promoter and thereby acts to increase mRNA synthesis. • Maltose operon is an example

  16. Maltose operon

  17. Global Control Catabolite repression

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