1. Gene Regulation 1 CHAPTER 15 REGULATION OF GENE ACTIVITY

2. Gene Regulation 2Outline Prokaryotic Regulation  trp Operon  lac Operon Eukaryotic Regulation  Transcriptional Control  Posttranscriptional Control  Translational Control  Posttranslational Control Genetic Mutations  Cancer

3. Gene Regulation 3 Pg 252 Operon consist of three components  Promoter ­DNA sequence where RNA polymerase first attaches ­Short segment of DNA  Structural Genes ­One to several genes coding for enzymes of a metabolic pathway ­Translated simultaneously as a block ­Long segment of DNA  Operator ­DNA sequence where active repressor binds ­Short segment of DNA

4. Gene Regulation 4 Prokaryotic Regulation: The Operon Model Operon consist of three components  Promoter ­DNA sequence where RNA polymerase first attaches ­Short segment of DNA  Operator ­DNA sequence where active repressor binds ­Short segment of DNA  Structural Genes ­One to several genes coding for enzymes of a metabolic pathway ­Translated simultaneously as a block ­Long segment of DNA

5. 5 The trp Operon

6. Gene Regulation 6 Repressible Operons: The trp Operon The regulator codes for a repressor If tryptophan (an amino acid) is absent:  Repressor is unable to attach to the operator (expression is normally “on”)  RNA polymerase binds to the promoter  Enzymes for synthesis of tryptophan are produced If tryptophan is present:  Combines with repressor as corepressor  Repressor becomes functional  Blocks synthesis of enzymes and tryptophan

7. Gene Regulation 7 trp Operon Animations  Animation #1 Animation #1 Animation #1  Animation #2 Animation #2 Animation #2

8. 8 The lac Operon

9. Gene Regulation 9 Inducible Operons: The lac Operon The regulator codes for a repressor If lactose (a sugar that can be used for food) is absent:  Repressor attaches to the operator  Expression is normally “off” If lactose is present:  It combines with repressor and renders it unable to bind to operator  RNA polymerase binds to the promoter  The three enzymes necessary for lactose catabolism are produced

10. 10 Action of CAP

11. Gene Regulation 11 Lac Operon Animations  Animation #1 Animation #1 Animation #1  Lac Operon Induction & Quiz Lac Operon Induction & Quiz Lac Operon Induction & Quiz

12. Gene Regulation 12 Negative vs Positive Control 1.Negative Control - Active repressors shut down activity of an operon 2.Positive Control - when CAP molecule is active, it promotes activity of operon.  Use of both positive and negative controls allows cell to fine-tune its control of metabolism.

13. Gene Regulation 13 Eukaryotic Regulation A variety of mechanisms Five primary levels of control:  Nuclear levels ­Chromatin Packing ­Transcriptional Control ­Posttranscriptional Control  Cytoplasmic levels ­Translational Control ­Posttranslational Control

14. 14 Five primary levels of control:  Nuclear levels ­Chromatin Packing ­Transcriptional Control ­Posttranscriptional Control  Cytoplasmic levels ­Translational Control ­Posttranslational Control Regulation of Gene Expression: Levels of Control in Eukaryotes

15. Gene Regulation 15 Chromatin Structure Eukaryotic DNA associated with histone proteins  Together make up chromatin  As seen in the interphase nucleus Nucleosomes:  DNA wound around balls of eight molecules of histone proteins  Looks like beads on a string  Each bead a nucleosome The levels of chromatin packing determined by degree of nucleosome coiling

16. 16 Levels of Chromatin Structure Eukaryotic DNA associated with histone proteins  Together make up chromatin  As seen in the interphase nucleus

17. 17 Figure 15.5cNucleosomes:  DNA wound around balls of eight molecules of histone proteins  Looks like beads on a string  Each bead a nucleosome The levels of chromatin packing determined by degree of nucleosome coiling

18. Gene Regulation 18 Chromatin Packing Euchromatin  Loosely coiled DNA  Transcriptionally active Heterochromatin  Tightly packed DNA  Transcriptionally inactive

19. 19 X-Inactivation in Mammalian Females Barr Bodies - Animation Animation  Females have two X chromosomes, but only one is active  Other is tightly packed along its entire length  Inactive X chromosome is Barr body

20. 20 Initiation of Transcription Transcription controlled by proteins called transcription factors  Bind to enhancer DNA  Regions of DNA where factors that regulate transcription can also bind  Always present in cell, but most likely have to be activated before they will bind to DNA

21. Gene Regulation 21 Transcriptional Control Transcription controlled by proteins called transcription factors  Bind to enhancer DNA  Regions of DNA where factors that regulate transcription can also bind  Always present in cell, but most likely have to be activated before they will bind to DNA

22. 22 Lampbrush Chromosomes These chromosomes are present in maturing amphibian egg cells and give evidence that when mRNA is being synthesized, chromosomes most likely decondense. Each chromosome has many loops extended from its axis (white). Many mRNA transcripts are being made off these DNA loops (red)

23. Gene Regulation 23 Posttranscriptional Control Posttranscriptional control operates on primary mRNA transcript Given a specific primary transcript:  Excision of introns can vary  Splicing of exons can vary  Determines the type of mature transcript that leaves the nucleus May also control speed of mRNA transport from nucleus to cytoplasm  Will affect the number of transcripts arriving at rough ER  And therefore the amount of gene product realized per unit time

24. 24 Processing of mRNA Transcripts  Excision of introns can vary  Splicing of exons can vary  Determines the type of mature transcript that leaves the nucleus Control speed of mRNA transport from nucleus to cytoplasm  Will affect the number of transcripts arriving at rough ER  And therefore the amount of gene product realized per unit time

25. Gene Regulation 25 Translational Control Translational Control - Determines degree to which mRNA is translated into a protein product  Presence of 5′ cap  Length of poly-A tail on 3′ end Posttranslational Control - Affects the activity of a protein product  Activation  Degradation rate

26. Gene Regulation 26 Post-Translational Control Posttranslational Control begins once a protein has been synthesizedPosttranslational Control begins once a protein has been synthesized  Some Proteins are not immediately active after synthesis. ­Cleaving and recombining  Some proteins are short-lived ­Degraded and Destroyed (Proteasomes)

27. Gene Regulation 27 Effect of Mutations on Protein Activity Point Mutations  Involve change in a single DNA nucleotide  Changes one codon to a different codon  Affects on protein vary: ­Nonfunctional ­Reduced functionality ­Unaffected

28. Gene Regulation 28 Effect of Mutations on Protein Activity Frameshift Mutations  One or two nucleotides are either inserted or deleted from DNA  Protein always rendered nonfunctional Normal : THE CAT ATE THE RAT After deletion: THE ATA TET HER AT After insertion: THE CCA TAT ETH ERA T

29. 29 Point Mutation

30. 30 Androgen Insensitivity Female Appearance Male Karyotype Testes instead of ovaries & uterus in abdominal cavity Mutation – makes cells unable to respond to male sex hormone. The androgen receptor is ineffective

31. Gene Regulation 31Carcinogenesis Development of cancer involves a series of mutations Proto-oncogenes – Stimulate cell cycle Tumor suppressor genes – inhibit cell cycle Mutation in oncogene and tumor suppressor gene: ­Stimulates cell cycle uncontrollably ­Leads to tumor formation

32. 32 Carcinogenesis

33. 33 Achondroplasia and Xeroderma Pigmentosum

34. Gene Regulation 34 Causes of Mutations Replication Errors  1 in 1,000,000,000 replications  DNA polymerase ­Proofreads new strands ­Generally corrects errors Environmental Mutagens  Carcinogens - Mutagens that increase the chances of cancer ­Ultraviolet Radiation ­Tobacco Smoke

35. Gene Regulation 35Review Prokaryotic Regulation  trp Operon  lac Operon Eukaryotic Regulation  Transcriptional Control  Posttranscriptional Control  Translational Control  Posttranslational Control Genetic Mutations  Cancer

36. Gene Regulation Ending Slide Chapter 15