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Ch 11 gene expression lecture presentation


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Ch 11 gene expression lecture presentation

  1. 1. Chapter 11 GENE EXPRESSION
  2. 2. Gene Expression in Eukaryotes <ul><li>Gene expression – the activation of a gene that results in the formation of a gene </li></ul><ul><li>Transcription causes expression </li></ul><ul><li>Important for cellular control and differentiation. </li></ul>
  3. 3. General Mechanisms <ul><li>1. Regulate Gene Expression </li></ul><ul><li>2. Regulate Enzyme Activity </li></ul>
  4. 4. Initiating Transcription
  5. 5. Operon Model <ul><li>Jacob and Monod (1961) - Prokaryotic model of gene control. </li></ul>
  6. 6. Operon Structure <ul><li>1. Regulatory Gene </li></ul><ul><li>2. Operon Area </li></ul><ul><ul><li>a. Promoter </li></ul></ul><ul><ul><li>b. Operator </li></ul></ul><ul><ul><li>c. Structural Genes </li></ul></ul>
  7. 7. Regulatory Gene <ul><li>Makes Repressor Protein which may bind to the operator. </li></ul>
  8. 8. Promoter <ul><li>Attachment sequence on the DNA for RNA polymerase. </li></ul>
  9. 9. Operator <ul><li>The &quot;Switch”, binding site for Repressor Protein. </li></ul><ul><li>If blocked, will not permit RNA polymerase to pass, preventing transcription. </li></ul>
  10. 11. Structural Genes <ul><li>Make the enzymes for the metabolic pathway. </li></ul>
  11. 12. Lac Operon <ul><li>For digesting Lactose. </li></ul><ul><li>Inducible Operon - only works (on) when the substrate (lactose) is present. </li></ul>
  12. 13. If no Lactose <ul><li>Repressor binds to operator. </li></ul><ul><li>Operon is &quot;off”, no transcription, no enzymes made </li></ul>
  13. 14. If Lactose is absent
  14. 15. If Lactose is present <ul><li>Repressor binds to Lactose instead of operator. </li></ul><ul><li>Operon is &quot;on”, transcription occurs, enzymes are made. </li></ul>
  15. 16. If Lactose is present
  16. 17. Enzymes <ul><li>Digest Lactose. </li></ul><ul><li>When enough Lactose is digested, the Repressor can bind to the operator and switch the Operon &quot;off”. </li></ul>
  17. 18. Net Result <ul><li>The cell only makes the Lactose digestive enzymes when the substrate is present , saving time and energy. </li></ul>
  18. 19. Repressible Operons <ul><li>Are examples of Feedback Inhibition. </li></ul><ul><li>Result - keeps the substrate at a constant level. </li></ul>
  19. 20. CELL DIFFERENTIATION <ul><li>Development of specialized cells </li></ul><ul><li>Homeotic Genes – determine where certain anatomical structures such as appendages will occur </li></ul><ul><ul><li>Ex HOX genes –control position front/back/top/bottom </li></ul></ul>
  20. 21. Gene Expression and Cancer <ul><li>Cancer - loss of the genetic control of cell division. </li></ul><ul><li>Balance between growth-stimulating pathway (accelerator) and growth-inhibiting pathway (brakes). </li></ul>
  21. 23. Proto-oncogenes <ul><li>Normal genes for cell growth and cell division factors. </li></ul><ul><li>Genetic changes may turn them into oncogenes (cancer genes). </li></ul><ul><li>Ex: Gene Amplification, Translocations, Transpositions, Point Mutations </li></ul>
  22. 24. Proto-oncogenes
  23. 25. Tumor-Suppressor Genes <ul><li>Genes that inhibit cell division. </li></ul><ul><li>Ex - p53, p21 </li></ul>
  24. 26. Cancer Examples <ul><li>p53 - involved with several DNA repair genes and “checking” genes. </li></ul><ul><li>When damaged (e.g. cigarette smoke), can’t inhibit cell division or cause damaged cells to apoptose. </li></ul>
  25. 27. Carcinogens <ul><li>Agents that cause cancer. </li></ul><ul><li>Ex: radiation, chemicals </li></ul><ul><li>Most work by altering the DNA, or interfering with control or repair mechanisms. </li></ul>