1 / 29

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

shadow
Download Presentation

Outline

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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

More Related