GENE REGULATION

1. GENE REGULATION VS. aka. when to turn genes on!

2. Consider the difference: • Prokaryotic cells exist AS ONE CELL • That’s right… ONE CELL DOES IT ALL!

3. Consider the difference: • Prokaryote genes are regulated via. Transcriptional control

4. This means that genes are turnedon and off in response to the need of a particular gene product(s) at a particular time

5. This is different than EUKARYOTES • Eukaryotic cells have a long life span, during which they may need to respond repeatedly to many different stimuli. • New enzymes are not synthesized eachtime the cells respond to a stimulus

6. EUKARYOTES • Most enzymes & proteins are transformed from an inactive state to an active state, there is a RESERVE. • Some eukaryotic cells have a large store of inactive mRNA

7. THINK ABOUT IT… • RBC’s produce hemoglobin (O2 transporting protein) • Muscle cells produce myoglobin (O2 storing protein)

8. THINK ABOUT IT… • BOTH CELLS HAVE GENES THAT WILL NEVER BE USED.. IT WOULD BE WASTEFUL TO MAKE HEMOGLOBIN IF YOU WERE A MUSCLE CELL

9. it is different in prokaryotes prokaryotic genome

10. e. coli is a bacterium common in intestines

11. It has 4288 genes that code for proteins… some are always needed (ex. glycolysis enzymes) Some are needed only when there are certain environmental conditions

12. An E. coli living in an adult cow intestine is not normally exposed to LACTOSE (disaccharide) HOWEVER, if you were in the colon of a calf… lactose would be a primary energy source.

13. Should the E. coli invest energy and materials to produce lactose-metabolizing enzymes just IN CASE it ends up in the digestive system of a calf?

14. HOW can an individual bacterium, locked into the genome that it has inherited… cope with the ever “changing” environment??????

15. Turns out, the three genes to produce enzymes for lactose metabolism are found together in a complex

16. These three genes, turns out, are linked by a common control mechanism

17. Operon • A gene complex, consisting of a group of genes w/ related functions • & DNA sequences that control them.

18. Operon This is the mechanism by which bacteria control gene expression

19. Operon Model • Jacob and Monod (1965 Nobel Prize for physiology or medicine) - for their discovery of the Prokaryotic model of gene control. • Always on the national AP Biology exam !

20. So, if you remember… to use lactose as an energy source…

21. The lactose is cleaved by enzyme galactosidase… Another enzyme then converts galactose to glucose

22. And still athird enzyme (function not clear) is needed to complete the process for glucose to move across the cell membrane

23. E. Coli growing on glucoseproduces very little galactosidase… NO NEED!!

24. However, when grown on lactose, there are SEVERAL THOUSAND galactosidase molecules

25. Bacteria can, in one sweep, turn off or on genes that code for the production of these enzymes

26. Operon Model 1. Operon Area a. Operator b. Promoter (where RNA polymerase binds to DNA to begin transcription) c. Structural Genes 2. Regulatory Gene

27. Operon Structure 1. Operon Area a. Operator b. Promoter c. Structural Genes

28. OPERON AREA OPERATOR -> PROMOTER -> GENES THEY CONTROL

29. Operator- segment of DNA that “turns on” the RNA polymerase that is binding to the gene coding area

30. Pix of switch here OPERATOR Segment of DNA that “turns on” the ability for RNA polymerase to bind these genes

31. Pix of switch here OPERATOR If blocked, will NOT permit RNA polymerase to pass - preventing transcription of genes

32. Promotor- area where RNA polymerase binds to the DNA

33. OPERATOR OFF If blocked, will NOT permit RNA polymerase to pass - preventing transcription RNA polymeraseblocked

34. OperatorON RNA polymerase not blocked

35. OperatorON RNApolymerase can bind to promotor

36. OperatorON via. RNApolymerase Genestranscribed

37. OPERATOR -> PROMOTER -> GENES THEY CONTROL ->

38. 2. Regulatory Gene - codes for repressormolecules (this is upstream)

39. RepressorProtein - switches OFF the Operator and the OPERON cannot be transcribed In this case, continuously made by the regulatory gene

40. RepressorProtein - switches OFF the operon RNApolymerase cannot move down the operon

41. RepressorProtein - switches OFF the operon RNApolymerase no mRNA made - no enzymes made

42. (no breakdown of lactose) ex. lacOperon - codes for three genes that function in the production of an enzyme that breakdowns the disaccharide lactose

43. (no breakdown of lactose) lacOperon - usually off, only works when substrate (in this case: lactose) is present

44. Promoter - (remember) area where RNA polymerase binds to the DNA to promote transcription

45. Genes- plural… code for enzymes that break down lactose

46. repressor withnolactoseinthesystem ->regulatory gene codes for repressor.repressor binds to operator - no RNA polymerase attachment - no digestive enzyme made- NO NEED`

47. inducer withlactosepresent - inducer (an isomer of lactose) binds allosterically to therepressor

48. inducer withlactosepresent - shape change, and the DNA no longer recognizes the repressor

49. inducer withlactosepresent - RNA polymerase actively transcribesthe structural genes

50. inducer • When enough Lactose has been digested, the Repressor binds again to the Operator and switches the Operon "off”… no digestive enzymes made.