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Outline

Outline. Prokaryotic Regulation trp Operon lac Operon Eukaryotic Regulation Transcriptional Control Posttranscriptional Control Translational Control Posttranslational Control Genetic Mutations Cancer. Prokaryotic Regulation: The Operon Model. Operon consist of three components

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Outline

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  1. Gene Regulation

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

  3. 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

  4. 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

  5. The trp Operon

  6. 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

  7. The lac Operon

  8. Action of CAP

  9. 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

  10. Regulation of Gene Expression:Levels of Control in Eukaryotes

  11. 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

  12. Levels of Chromatin Structure

  13. Chromatin Packing • Euchromatin • Loosely coiled DNA • Transcriptionally active • Heterochromatin • Tightly packed DNA • Transcriptionally inactive • Barr Bodies • Females have two X chromosomes, but only one is active • Other is tightly packed along its entire length • Inactive X chromosome is Barr body

  14. X-Inactivation in Mammalian Females

  15. 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

  16. Lampbrush Chromosomes

  17. Initiation of Transcription

  18. 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

  19. Processing of mRNA Transcripts

  20. 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

  21. Effect of Mutations onProtein 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 • 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

  22. Point Mutation

  23. Androgen Insensitivity

  24. Carcinogenesis • 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

  25. Carcinogenesis

  26. Achondroplasia andXeroderma Pigmentosum

  27. 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

  28. Review • Prokaryotic Regulation • trp Operon • lac Operon • Eukaryotic Regulation • Transcriptional Control • Posttranscriptional Control • Translational Control • Posttranslational Control • Genetic Mutations • Cancer

  29. Gene Regulation

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