Chapter 16 Control of Gene Expression

1. Chapter 16Control of Gene Expression

2. Topics to discuss • DNA binding proteins • Prokaryotic gene regulation • Lac operon • Trp operon • Eukaryotic gene regulation Today’s lecture

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

5. Prokaryotic Gene Regulation Nutritional enviroment and a bug’s growth!

6. Operons • Operons provide coordinate expression

7. A model operon

8. Now let’s look at 2 groups of operons • Negative inducible operons • Negative repressible operons

9. Negative inducible operon INDUCIBLE

10. Turned on

11. repressor

12. Now let’s look at 2 specific operons • The Lactose operon • The Tryptophan operon

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

14. 1. Disaccharide 2. Monosaccharide Lactose Glucose 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. Negative inducible operon

20. Conditions: No glucose but lactose is present

21. Lactose Metabolism Requires Coordination of all these genes!

22. Laboratory Exercise: Mutational Analysis of the lac operon

23. Try out your ability to reason through the questions.

24. Predict if you expect to obtain the proteins from the lacZ and lacY genes IF certain mutations are present in the operon.

25. The next three slides are the “key” to the mutations.

26. Mutational Key: • Any + means wildtype. • Any – means mutant. • Two other mutants: “Oc and Is” • I- cells synthesize full levels in the presence or absence of inducer-Transcription Turned ON. Inhibitor cannot bind to DNA • P- the DNA promoter mutation : cannot bind RNA polymerase Transcription OFF • Is super-suppressors can bind DNA but not inducer. DNA and Transcription Turned OFF. • Oc is an DNA mutation: repressor cannot bind. Transcription ON.

27. Examples I s=the Super-repressor Allolactose CANNOT BIND VERSUS DNA binding site I - = DNA binding site mutated, prevents binding, allows transcription

28. Next: 3 important terms of DNA control. • Constitutive activity • Trans acting • Cis acting

29. No Lactose - 1 + 2 3 4 5 6 7 8 9

30. Negative inducible operon

31. Question: what happens when both lactose and glucose are present together in the same cell?

32. To answer this question you first need to understand this reaction Adenylyl cyclase Cyclic AMP ATP + catabolite activator protein (helix-turn-helix) Glucose may inhibit this enzyme

33. cAMP and glucose levels are inversely proportional.

35. The promoter needs to be in an ideal conformation for RNA polymerase.

36. How CAP and cAMP affects the promoter END of PART I

37. Trypthophan Operon

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

39. Negative repressible operon

40. 2 shapes to the mRNA

42. attenuation

43. Eukaryotic Gene Regulation

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

46. Changes in Chromatin structure and eukaryotic gene regulation • Chromatin Structure • DNase hypersensitivity ( • Histone acetylation • DNA methylation