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WEEK 14

WEEK 14. CHAPTER 13 (Gene Regulation) Pages 233-245 EXAM IV is NEXT WEEK , MAY 24 th (LAST EXAM) 6pm SHARP!!. Last Week. Molecular Biology of the Gene. This Week. Prokaryotic Regulation of Gene Activity Eukaryotic Regulation of Gene Activity Animal Development.

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WEEK 14

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  1. WEEK 14 CHAPTER 13 (Gene Regulation) Pages 233-245 EXAM IV is NEXT WEEK, MAY 24th(LAST EXAM) 6pm SHARP!!

  2. Last Week Molecular Biology of the Gene This Week Prokaryotic Regulation of Gene Activity Eukaryotic Regulation of Gene Activity Animal Development

  3. GENE RegulationHow are genes regulated?What causes one gene to differ from another?

  4. Prokaryotic Gene Regulation • 1961- Jacob and Monod receive Nobel Prize for their work with E. coli structural gene regulation • Created the “OPERON” model

  5. GENE EXPRESSION: is the process by which information from a gene is used in the synthesis of a functional gene product (ex. Protein)

  6. OPERONS Include: • Promoter - Short sequence of DNA where RNA pol. attaches to begin transcription • Operator • Short portion of DNA where an active repressor binds • Does not allow RNA pol to attach no transcription • Controls transcription of structural genes • Structural Genes - 1 or more genes coding for the primary structure of enzymes in a metabolic pathway transcribed together

  7. OPERON STRUCTURE OPERON Regulator Gene Operator Structural Genes DNA Promoter Promoter for Regulator Gene • Regulator Gene • Located outside of the operon • Controlled by its own promoter • Codes for a repressor • Repressor controls activity of operon OPERON -Promoter -Operator -Structural Genes

  8. General Operon Function

  9. Two Well Known Operons • The trp Operon - Found in E. coli • The repressor is normally unable to attach • RNA pol binds to promoter and genes are expressed • Operon exists in the “on” condition • The lac Operon • Repressor is normally attached • In the absence of glucose and in presence of lactose, repressor binds to lactose, changes shape and is unable to bind to the promoter • RNA pol binds instead and transcription occurs

  10. trp Operon- In absence of tryptophan, enzymes are needed RNA polymerase binds to the promoter region Transcription proceeds Necessary enzymes are made for use in the cell

  11. trp operon = REPRESSIBLE operon In presence of tryptophan, enzymes are not needed Tryptophan binds to the repressor (is a “corepressor”) Change in shape of repressor allows for repressor to bind to the operator RNA polymerase unable to attach to promoter Genes are not expressed

  12. The lacoperon Is an example of an INDUCIBLE operon (it is induced to be “on”) IN ABSENCE OF LACTOSE, STRUCTURAL GENES ARE NOT EXPRESSED

  13. lac operon In presence of lactose, the structural genes are expressed Lactose binds to the repressor which falls away from the operator allowing RNA pol to bind to the promoter

  14. trp operon = Repressiblelac operon = Inducible

  15. lac operon • 3 enzymes are produced when E. coli is denied glucose and is given lactose • Beta-galactosidase (breaks down disaccharide to galactose) • Permease (facilitates entry of lactose into the cell) • Transacetylase (aids in lactose metabolism)

  16. lac operon Catabolic metabolism breaks down nutrients Why have an inducible operon? Because the enzymes that are produced in the presence of the inducer (lactose) need only be active when lactose is present Allows for immediate adaptation to undergo metabolism in different environments

  17. lac operon E. coli preferentially breaks down glucose In absence of glucose molecule cyclic AMP (cAMP) accumulates cAMP is derived from ATP Phosphate group attaches in two places

  18. lac operon cAMP binds to catabolite activator protein (CAP) When lactose is present cAMP/CAP complex binds to the CAP binding site and RNA pol is better able to bind to the promoter

  19. lac operon When glucose is present there is little cAMP in the cell and CAP is inactive RNA pol does not completely bind to promoter Lactose enzyme production decreases When both glucose and lactose are present, cell preferentially metabolizes glucose

  20. WHY IS IT ADVANTAGEOUS FOR PROKARYOTES TO ORGANIZE GENES IN AN “OPERON” IN THIS MANNER? Energy is not wasted producing molecules that are not needed Able to adapt to changing environments

  21. Eukaryotic Regulation of Gene Activity

  22. Different cells express different genes • Ex. Nerve cell gene expression is different from muscle cell gene expression • GENE EXPRESSION: • GENE  Functional Protein Product • 5 levels of gene expression control • Expression is controlled from transcription to protein activity

  23. 5 Levels of Gene Expression Control • Chromatin Structure • The packaging of chromatin within the nucleus keeps genes turned “off” • RNA polymerase is not able to bind • Chromatin structure is “epigenetic”- non-genetic factors influence the inheritance of a phenotype or how genes are expressed

  24. 5 Levels of Gene Expression Control • Transcriptional Control • Transcription factors control the amount of gene product that is made • Transcription factors promote or repress transcription • Posttranscriptional Control • mRNA processing (splicing) and how fast mRNA leaves the nucleus • Also affects amount of gene product produced within a given time period

  25. 5 Levels of Gene Expression Control • Translational Control • Occurs in the cytoplasm • Affects when translation begins • Posttranslational Control • Occurs in the cytoplasm • Occurs after protein synthesis • Gene product, the functional protein, may undergo changes to become fully functional

  26. 5 Levels of Eukaryotic Gene Regulation: • Chromatin Structure • Transcriptional Control • Posttranscriptional Control • Translational Control • Posttranslational Control 1 2 3 4 5

  27. Transcriptional Control • DNA must be available (in a non-condensed form for RNA pol to attach) • Transcription factors (proteins)- Regulate transcription • Transcription activators (proteins)- Speed up transcription • Enhancer- A specific region of DNA some distance from the promoter region of the gene

  28. Transcriptional Control

  29. Posttranscriptional Control • Alternative mRNA splicing • Involves the control of the speed of mRNA leaving the nucleus • The pre-mRNA can produce several different mRNAs depending on how the it is spliced

  30. Posttranscriptional Control

  31. Translational Control • Begins as the processed mRNA reaches the cytoplasm • Micro RNAs (miRNAs)- non-protein coding RNAs that regulate translation by causing the inhibition or destruction of mRNAs before they can be translated

  32. Translational Control

  33. Posttranslational Control • Control starts once a protein is synthesized • Some proteins must be “activated” after they are synthesized • Activation can be done by disulfide bonding or protein folding

  34. PLEASE WELCOME:Soon to be Dr. …BARBARA JUNCOSA, A.B.D.The Rockefeller UniversityNew York, NY

  35. Gene Mutations and Regulation What is a gene mutation? • A permanent change in the sequence of bases in DNA How do mutations arise? • Spontaneously • Induced

  36. Spontaneous Mutations • Mispairing during replication • Disruption of a gene due to the relocation of a transposon • Chemical change • One mistake occurs for every 1 billion nucleotide base pairs thanks to the efficiency of DNA polymerase • Spontaneous mutations are VERY RARE!!

  37. Induced Mutations Caused by mutagens- - Environmental factors that can alter the base composition of DNA Ex. Radiation, organic chemicals (mercury!) Many mutagens are carcinogens- cancer causing Ex. Food additives, tobacco smoke, acrylamide (naturally found in french fries), x-rays, gamma rays, free radicals, UV radiation

  38. How can we test for mutagenicity? Mutagenicity= ability of a chemcial to be carcinogenic Scientists use the AMES test to determine if a chemical is carcinogenic

  39. AMES TEST A bacterial strain is used that requires Histidine to grow If the chemical is Mutagenic, the bacteria Can grow w/o histadine The control has no Histadine and cannot Grow The mutagen allows for the bacteria to grow w/o the presence of histadine

  40. DNA Repair Enzymes • In the event of a mutagenic change in DNA, DNA REPAIR ENZYMES monitor and repair damaged DNA • In some cases, DNA repair is not possible and the mutation is not fixed causing disease and/or cancer

  41. Mutations and Protein Activity Types of mutations that effect protein activity: • Point mutations • Change in a single DNA nucleotide • Ex. Sickle-cell disease is caused by a single change in a base which leads to a change in an amino acid from glutamic acid (normal) to valine (not normally present)  stiff RBCs/ sickle shaped

  42. 2. Frameshift Mutations • Caused by the insertion or deletion of one or more nucleotides into or from DNA • Causes the re-coding of CODONS Ex. THE CAT ATE THE RAT (triplet codons) If the letter C is deleted: THE ATA TET HER AT  This makes no sense!

  43. Frameshift Mutation Example U is removed

  44. Non Functional Proteins • Point mutations and frameshift mutations can lead to non-functioning proteins What happens when a protein does not function? - Enzymes might not be able to convert one kind of chemical into another

  45. If a person inherits a faulty code for Enzyme A (EA), then for ex. Phenylalanine can not be converted into tyrosine Excess phenylalanine build up can lead to mental retardation This genetic disorder is known as PKU – phenylketonuria If a person inherits a faulty Enzyme B (EB), but has a functioning EA, then the person will be ALBINO

  46. Mutations can cause cancer

  47. ONCOGENE = a gene having the potential to cause a normal cell to become cancerous

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