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Gene Regulation

Gene Regulation. … on / off … fast / slow. Summary: When and where do cells have control over which genes are expressed and which proteins are active?. Proteins determine when and how often RNA polymerase can bind. Modifications to pre-mRNA affect the life and use of RNA in the cytoplasm.

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Gene Regulation

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  1. Gene Regulation … on / off … fast / slow

  2. Summary:When and where do cells have control over which genes are expressed and which proteins are active? Proteins determine when and how often RNA polymerase can bind Modifications to pre-mRNA affect the life and use of RNA in the cytoplasm Proteins are activated through processing and signals can enlist cellular machinery to destroy proteins

  3. Newer Ideas to Look For • The study of epigenetics investigates ways that whole sections of chromosomes are activated and deactivated.

  4. Looking at Individual Genes • The simplest and most well understood model of the regulation of individual genes is found in prokaryotes. • We will study two examples of gene control in E. coli; a bacteria found in the human digestive tract

  5. FEED ME!

  6. The Operon Control Region Coding Region: Gene(s) Operon

  7. The Lac Operon in E. coli Control Region Genes Produce the enzymesnecessary for digesting lactose Respond to the presence or absence of lactose and glucose

  8. The Lac Operon in E. coli Binding site for RNAP lacZ lacY lacA promoter activator operator (CAP binding site) Each lac gene codes for an enzyme only needed when lactose is present ON FAST OFF SLOW

  9. The Lac Operon in E. coli

  10. The Lac Operon in E. coli • With no proteins bound to either the operator or activator regions, RNAP is free to bind to the promoter and transcribe the genes lacZ lacY lacA A P O pre-mRNA

  11. The Lac Operon in E. coli • If there is no lactose present, this would be a waste of valuable resources like ATP and amino acids lacZ lacY lacA A P O pre-mRNA

  12. The Lac Operon in E. coli • To prevent transcription, the genes can be “turned off” when a repressor proteinis bound to the operator sequence repressor lacZ lacY lacA A P O GET OUT OF THE WAY!

  13. The Lac Operon in E. coli • When lactose is present, it will bind to the repressor, change its 3D shape and remove it from the operator. lacZ lacY lacA A P O

  14. The Lac Operon in E. coli • When lactose is present, it will bind to the repressor, change its 3D shape and remove it from the operator. lacZ lacY lacA A P O

  15. The Lac Operon in E. coli • RNAP is now free to bind the promoter and transcribe the sequence lacZ lacY lacA A P O

  16. The Lac Operon in E. coli • Since the presence of lactose removes the repressor and “turns on” the genes, lactose is called an inducer. lacZ lacY lacA A P O repressor inducer

  17. What it “really” looks like

  18. The Lac Operon in E. coli Operon is OFF lacZ lacY lacA A P O

  19. The Lac Operon in E. coli Operon is ON lacZ lacY lacA A P O

  20. The Lac Operon in E. coli • Glucose is the preferred energy source for cells OM NOM NOMNOMNOM glucose Cell lactose

  21. The Lac Operon in E. coli • If glucose levels are LOW, lactose metabolism is prioritized • If glucose levels are HIGH, lactose metabolism is of lower priority How can glucose levels be detected in the nucleus? LOW HIGH cyclic AMP (cAMP) glucose

  22. cAMP and CAP • cAMP binds to the activator protein “CAP” (Catabolite activator protein) • Together they will bind to DNA ahead of the promoter to help RNAP bind

  23. cAMP and CAP • When glucose levels are low, cAMP activated CAP proteins will stimulate the transcription of over 100 genes including the lac operon

  24. The Lac Operon in E. coli • Without the cAMP-CAP complex bound to the activator, RNAP is less likely to bind and produces fewer transcripts in a given time lacZ lacY lacA A P O “SLOW”

  25. The Lac Operon in E. coli • With the cAMP-CAP complex bound to the activator, RNAP binds more readily, speeding up the production of RNA transcripts lacZ lacY lacA A P O “FAST”

  26. 3D model of cAMP-CAP complex bound to DNA http://proteopedia.org/wiki/index.php/Catabolite_gene_activator_protein

  27. Summary FAST / SLOW ON / OFF glucose lactose   OFF   OFF lacZ lacZ lacZ lacZ lacY lacY lacY lacY lacA lacA lacA lacA A A A A P P P P O O O O   FAST ON   SLOW ON

  28. The trp Operon in E. coli • If ingested levels of theamino acid tryptophanare low, e. coli is ableto synthesize it on its own. • When tryptophan levels are low, the try operon is turned on to make the enzymes necessary to synthesize more.

  29. The trp Operon in E. coli • Again, the cells should not waste resources making more tryptophan if it is already present

  30. The trp Operon in E. coli • No tryptophan = operon on • Enzymes are synthesized to make trp P O trpE trpD trpC trpB trpA

  31. The trp Operon in E. coli • Tryptophan present = operon off • Trp is a co-repressor(needed for repressor to function) repressor P O trpE trpD trpC trpB trpA co-repressor

  32. What it “really” looks like

  33. Negative gene regulation • Repressors are used to turn off genes repressor lacZ lacY lacA A P P O O trpE trpD trpC trpB trpA co-repressor repressor inducer

  34. Negative Gene RegulationThe lac Operon

  35. Positive Gene RegulationThe lacOperon

  36. On your own, summarize the post transcriptional and post translational control cells have over their genes using your textbook

  37. Co-Repressor

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