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Understanding Gene Expression Control Mechanisms: From Prokaryotes to Eukaryotes

Explore DNA-binding proteins and mechanisms of gene regulation in prokaryotes and eukaryotes. Learn about operons, lac operon, trp operon, and regulatory proteins. Discover how chromatin structure and RNA silencing affect eukaryotic gene regulation.

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Understanding Gene Expression Control Mechanisms: From Prokaryotes to Eukaryotes

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  1. Chapter 16Control of Gene Expression

  2. Topics to discuss • DNA binding proteins • Prokaryotic gene regulation • negative inducible: lac operon • negative repressible: trp operon • Eukaryotic gene regulation

  3. 6 groups of DNA-binding regulatory proteins have been identified

  4. Prokaryotic Gene Regulation

  5. Operons • Operons provide coordinate expression

  6. A model operon

  7. Now let’s look at 2 (of four) groups of operons • Negative inducible operons • Negative repressible operons

  8. Negative inducible operon INDUCIBLE

  9. Turned on

  10. repressor

  11. Now let’s look at 2 specific operons • The Lactose operon: negative inducible • The Tryptophan operon: negative repressible

  12. Francois Jacob and Jacques Monod 1961 • Studied lactose metabolism/operon in prokayotes J. Monod Won the Nobel Prize in 1965

  13. 1. Disaccharide 2. Monosaccharide Lactose Glucose Sources of prokaryotic energy

  14. Monosaccharide Disaccharide Glucose Lactose Sources of prokaryotic energy

  15. Building the lac operon

  16. Lac Operon and Proposed Arrangement with control I gene I P O Z Y A Not technically part of the “operon”

  17. Lactose Metabolism Requires Coordination of all these genes!

  18. Negative inducible operon

  19. (assume only lactose is present)

  20. Next: let’s review just the pattern of expression when: • When only lactose is present. • When only glucose is present. • Glucose and lactose are present in the cell

  21. “Why does the presence of glucose influence lactose metabolism? Lac

  22. To answer this question you need to understand this reaction Adenylyl cyclase ATP Cyclic AMP + catabolite activator protein Glucose may inhibit this enzyme

  23. Now put the pieces all together.

  24. How CAP and cAMP affects the promoter

  25. So….Conditions: Only lactose is present

  26. But…Conditions: Only glucose

  27. And Finally….Glucose and Lactose

  28. Summary

  29. Trypthophan Operon • 5 genes involved in the synthesis of the amino acid trypthophan

  30. Negative repressible operon

  31. 2 shapes to the mRNA When trp is high When trp is low

  32. Ribosome does not stall

  33. Ribosome stalls

  34. Changes in Chromatin structure and eukaryotic gene regulation • Histone acetylation • DNA methylation • RNA silencing

  35. Do eukaryotes show coordinate gene regulation? Yes, the same response element may be found in related genes.

  36. Also remember gene expression through RNA interference!

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