PowerLecture: Chapter 15

1. Controls over Genes PowerLecture:Chapter 15

2. Loss of gene controls can be disastrous Some gene mutations, either inherited or spontaneously mutated due to environmental factors, predispose individuals to develop cancer ERBB2, a type of membrane receptor, is encoded on chromosome 17 This gene controls the cell cycle - overexpression or mutation triggers cancerous transformations Impacts, Issues: Between You and Eternity

3. BRCA1 and BRCA2 are tumor suppressing proteins that fix damaged DNA Breast cancer cells often contain their mutated forms Impacts, Issues: Between You and Eternity

4. Changes in DNA Trigger Cancer Ultraviolet radiation can cause breaks Can promote formation of dimers

5. Controlling the Cell Cycle Cycle has built-in checkpoints Proteins monitor chromosome structure, whether conditions favor division, etc. Proteins are products of checkpoint genes Kinases Growth factors

6. Oncogenes Have potential to induce cancer Mutated forms of normal genes Can form following insertions of viral DNA into DNA or after carcinogens change the DNA

7. Cancer Characteristics Plasma membrane and cytoplasm altered Cells grow and divide abnormally Weakened capacity for adhesion Lethal unless eradicated

8. Apoptosis Programmed cell death Signals unleash molecular weapons of self-destruction Cancer cells do not commit suicide on cue

9. Gene Control Which genes are expressed in a cell depends upon: • Type of cell • Internal chemical conditions • External signals • Built-in control systems

10. Mechanisms of Gene Control Controls related to transcription Transcript-processing controls Controls over translation Post-translation controls

11. Regulatory Proteins Can exert control over gene expression through interactions with: DNA RNA New polypeptide chains Final proteins

12. Control Mechanisms Negative control Regulatory proteins slow down or curtail gene activity Positive control Regulatory proteins promote or enhance gene activities

13. Control Mechanisms Promoters Enhancers

14. Chemical Modifications Methylation of DNA can inactivate genes Acetylation of histones allows DNA unpacking and transcription

15. Controls in Eukaryotic Cells Control of transcription Transcript processing controls Controls over translation Controls following translation

16. Controls in Eukaryotic Cells NUCLEUS CTYOPLASM translational control protein product pre-mRNA transcript mRNA mRNA DNA transport processing control mRNA transport control mRNA degradation control protein product control transcription control inactivated mRNA inactivated protein Fig. 15-3, p.233

17. Chromosome Puff • Portion of the chromosome in which the DNA has loosened up to allow transcription • Translation of transcripts from puffed region produces protein components of saliva

18. X Chromosome Inactivation One X inactivated in each cell of female Creates a “mosaic” for X chromosomes Governed by XIST gene

19. A condensed X chromosome (Barr body) in the somatic cell nucleus of a human female X Chromosome Inactivation Fig. 15-4a, p.234

20. Most Genes Are Turned Off Cells of a multicelled organism rarely use more than 5-10 percent of their genes at any given time The remaining genes are selectively expressed

21. Phytochrome Signaling molecule in plants Activated by red wavelengths, inactivated by far-red wavelengths Changes in phytochrome activity influence transcription of certain genes

22. petal carpel stamen sepal Fig. 15-6, p.235

23. B A C 1 2 3 4 petals carpel sepals stamens Fig. 15-6, p.235

24. Fig. 15-6, p.235

25. Fig. 15-6, p.235

26. Fig. 15-6, p.235

27. Fig. 15-6, p.235

28. Fig. 15-6, p.235

29. Homeotic Genes Occur in all eukaryotes Master genes that control development of body parts Encode homeodomains (regulatory proteins)‏ Homeobox sequence can bind to promoters and enhancers

30. Knockout Experiments Prevent a gene’s transcription or translation Differences between genetically engineered knockout individuals and wild-type individuals point to function of knocked out gene Knockout experiments shed light on genes that function in Drosophila development

31. Knockout Experiments Fig. 15-7c, p.237

32. Body Plan A7 A5 A3 A1 T2 T2 T2 A8 A4 A2 T3 T1 T2 A5 A6 A7 A8 A4 A3 A2 A1 Md T3 Mx T1 T2 Lb A8 A7 A6 T1 T2 A4 A3 A1 T3 A2 A5 A4 A3 A2 T1 T3 A1 T2 A6 A7 A8 Fig. 15-8a, p.237

33. Body Plan Fig. 15-8b, p.237

34. Body Plan Fig. 15-8c, p.237

35. Gene Control in Prokaryotes No nucleus separates DNA from ribosomes in cytoplasm When nutrient supply is high, transcription is fast Translation occurs even before mRNA transcripts are finished

36. The Lactose Operon operator regulatory gene gene 1 gene 2 gene 3 operator transcription, translation promoter lactose operon repressor protein Fig.15-10, p. 241

37. High Lactose allolactose lactose mRNA RNA polymerase gene 1 operator promoter operator Fig.15-10, p. 241

38. Low Lactose Repressor binds to operator Binding blocks promoter Transcription is blocked Fig.15-10, p. 241

39. CAP Exerts Positive Control CAP is an activator protein Adheres to promoter only when in complex with cAMP Level of cAMP depends on level of glucose

40. Positive Control – High Glucose There is little cAMP CAP cannot be activated The promoter is not good at binding RNA polymerase The lactose-metabolizing genes are not transcribed very much

41. Positive Control – Low Glucose cAMP accumulates CAP-cAMP complex forms Complex binds to promoter RNA polymerase can now bind The lactose-metabolizing genes are transcribed rapidly

42. Hormones Signaling molecules Stimulate or inhibit activity in target cells Mechanism of action varies May bind to cell surface May enter cell and bind to regulatory proteins May bind with enhancers in DNA

43. Polytene Chromosomes Occur in salivary glands of midge larvae Consist of multiple DNA molecules Can produce multiple copies of transcripts

44. Vertebrate Hormones Some have widespread effects Somatotropin (growth hormone)‏ Others signal only certain cells at certain times Prolactin stimulates milk production

45. Fig. 15-11a, p.241

46. Fig. 15-11b, p.241