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Gene Expression

Gene Expression. Why Regulate Gene Expression?. Response to changing developmental or environmental conditions Save… time energy raw materials. Feedback Inhibition Product inhibits enzyme function Regulation of transcription Product inhibits enzyme production. Prokaryotic Regulation.

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Gene Expression

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  1. Gene Expression

  2. Why Regulate Gene Expression? • Response to changing developmental or environmental conditions • Save… • time • energy • raw materials

  3. Feedback Inhibition Product inhibits enzyme function Regulation of transcription Product inhibits enzyme production Prokaryotic Regulation

  4. Research and Development Testing Production Distribution Drug Company MGMT

  5. Operon Regulation Inducible Repressible Default on Repressor inactive Turned off when product is present Repressor active Default off • Repressor active Turned on when substrate is present • Repressor inactive

  6. Inducible Operon Substrate Absent • Repressor protein binds to operator • Operon blocked • No substrate-catabolizing enzymes produced Default: OFF Substrate Present • Substrate inactivates repressor protein • Operon transcribed • Enzymes produced RG P O 1 2 3 RNAPoly

  7. Lac Operon

  8. Trp Operon

  9. Repressible Operon Product Absent • Repressor protein inactive • Operon transcribed • Product-anabolizing enzymes produced Default: ON Product Present • Product activates repressor protein • Operon blocked • No enzymes produced RG P O 1 2 3 RNAPoly

  10. Inducible, Repressible, Both, or Neither? • The Lac operon • Regulatory gene codes for repressor protein • Operon expressed (ON) by default • Substrate inactivates repressor protein • Product binds to RNA polymerase • Product activates repressor protein • Repressor protein status changes when bound by particles • Enzymes deactivate repressor protein • The Trpoperon • Operon blocked (OFF) by default • Active repressor protein blocks transcription • Repressor is created in an active state

  11. Inducible, Repressible, Both, or Neither? • The Lac operon I • Regulatory gene codes for repressor protein B • Operon expressed (ON) by default R • Substrate inactivates repressor protein I • Product binds to RNA polymerase N • Product activates repressor protein R • Repressor protein status changes when bound by particles B • Enzymes deactivate repressor protein N • The Trpoperon R • Operon blocked (OFF) by default I • Active repressor protein blocks transcription B • Repressor is created in an active state I

  12. Eukaryotic Regulation • Tend to have 10x the genes of prokaryotes • Expression is controlled at multiple points

  13. Heterochromatin Partially coiled Euchromatin Uncoiled Chromatin Modification

  14. Chromatin Modification • Methylation • Attachment of methyl groups to cytosine • HistoneAcetylation • Attachment of acetyl groups to histones • Loosens grip of histones on DNA

  15. Post-transcriptional Regulation • Alternative Splicing

  16. Post-transcriptional Regulation • RNA Degradation • Translation Blockage • Protein Degradation

  17. Code for proteins that stimulate division May become oncogenes (tumor-causing) Proto-oncogenes

  18. Code for proteins that inhibit division (Including density & anchorage dependence) Tumor Supressor Genes Tumor Supressor Gene Deletion

  19. Some viruses donate their genetic material Provirus may include an oncogene disrupt an tumor supressorgene make a promotor more active Carcinogenic Viruses Promoter Gene

  20. Review Questions Use no more than 1 word for each answer. • What type of organic molecule is a histone? • What is the structural difference between heterochromatin and euchromatin? • What does a proteasome do? • When expressed, what type of gene causes a cell to divide when it normally would not?

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