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Ecclesiastes 3:1

Ecclesiastes 3:1 1 To every thing there is a season, and a time to every purpose under the heaven:. Transcription: Concentrating on Prokaryotes. Timothy G. Standish, Ph. D. All Genes Can’t be Expressed At The Same Time.

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Ecclesiastes 3:1

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  1. Ecclesiastes 3:1 1 To every thing there is a season, and a time to every purpose under the heaven:

  2. Transcription:Concentrating on Prokaryotes Timothy G. Standish, Ph. D.

  3. All Genes Can’t be Expressed At The Same Time • Some gene products are needed by all cells all the time. These constitutive genes are expressed by all cells. • Other genes are only needed by certain cells or at specific times, expression of these inducible genes is tightly controlled in most cells. • For example, pancreatic b cells make insulin by expressing the insulin gene. If neurons expressed insulin, problems would result.

  4. Logical Expression Control Points Increasing cost • DNA packaging • Transcription • RNA processing • mRNA Export • mRNA masking/unmasking and/or modification • mRNA degradation • Translation • Protein modification • Protein transport • Protein degradation The logical place to control expression is before the gene is transcribed

  5. IntroductionThe Central Dogma of Molecular Biology Reverse transcription DNA Transcription Ribosome mRNA Translation Polypeptide (protein) Cell

  6. Stages of Transcription • Transcription can be logically divided into four distinct stages: • Template recognition • Initiation • Elongation • Termination • Each stage may participate in regulation, but template recognition and termination appear to be major players

  7. General Model For Transcription Core Enzyme a a  b s Holoenzyme RNA Polymerase

  8. General Model For Transcription a a  b s

  9. General Model For Transcription a a  b s

  10. General Model For Transcription a a  b s

  11. General Model For Transcription a a  b s NusA Top- Isomerase I Gyrase

  12. General Model For Transcription a a  b s NusA Ribosome Exo- nuclease Ribosome Top- Isomerase I Gyrase

  13. General Model For Transcription a a  b s NusA Exo- nuclease Ribosome Ribosome

  14. General Model For Transcription a a  b s NusA Exo- nuclease Ribosome

  15. General Model For Transcription a a  b s NusA Exo- nuclease Ribosome

  16. General Model For Transcription a a  b s NusA Exo- nuclease

  17. General Model For Transcription a a  b s NusA Exo- nuclease

  18. General Model For Transcription a a  b s NusA Exo- nuclease

  19. General Model For Transcription a a  b s NusA

  20. RNA Polymerase • RNA Polymerase is a spectacular enzyme; it performs the following functions: • Recognition of the promoter region • Melting of DNA (Helicase + Topisomerase) • RNA Priming (Primase) • RNA Polymerization • Recognition of terminator sequence

  21. Prokaryotic Transcription Initiation • The  subunit of prokaryotic RNA polymerase is necessary for promoter recognition and binding of RNA polymerase to the promotor • Different  subunits allow recognition of different types of promoters; thus the type of genes transcribed can be modulated by altering the types of  subunits which attach to RNA polymerase

  22. Prokaryotic Transcription Initiation P2 Different promoters RNA Pol.  P1 Heat Shock Gene Constitutive Gene

  23. Prokaryotic Transcription Initiation RNA Pol.  P1 Heat Shock Gene P2 Constitutive Gene Different promoters

  24. Transcription Termination There are two types of termination: • Rho dependent requires a protein called Rho, that binds to and slides along the RNA transcript. The terminator sequence slows down the elongation complex, Rho catches up and knocks it off the DNA • Rho independent termination depends on both slowing down the elongation complex with a hairpin and a U-rich region that destabilizes the elongation complex

  25. TerminationRho Independent RNA Pol. RNA Pol. RNA 5’ RNA 5’ Terminator

  26. TerminationRho Independent RNA Pol. RNA Pol. 5’ RNA Terminator RNA 5’

  27. TerminationRho Dependent RNA Pol. r r RNA Pol. RNA 5’ Terminator RNA 5’ The terminator sequence slows RNA polymerase

  28. TerminationRho Dependent RNA Pol. r Help, Rho hit me! RNA Pol. RNA 5’ r Terminator RNA 5’ Rho catches up with RNA polymerase

  29. TerminationRho Dependent RNA Pol. r r RNA Pol. 5’ RNA Terminator RNA 5’ The elongation complex disintegrates

  30. The End

  31. Transcription Coding (sense) strand 5’ 3’ 3’ 5’ Template (antisense) strand

  32. Transcription Coding (sense) strand 5’ 3’ 3’ 5’ RNA Pol. Template (antisense) strand 5’ RNA

  33. Transcription RNA Pol. Coding (sense) strand 5’ 3’ 3’ 5’ Template (antisense) strand 5’

  34. Products of Transcription • Transcription produces three major RNA products: 1 Ribosomal RNA (rRNA) - Several rRNAs are vital constituents of ribosomes 2 Transfer RNA (tRNA) - The molecule that physically couples nucleic acid codons with specific amino acids 3 Messenger RNA (mRNA) - The nucleic acid messenger that carries encoded information from genes on DNA to the protein manufacturing ribosomes

  35. Transfer RNA (tRNA) • Acts as the adapter molecule between the genetic code on mRNA and the protein “language” • 75-85 bases long • A specific amino acid is covalently linked at the 3’ end • Elsewhere on the molecule is an anticodon complimentary to the specific amino acid codon on mRNA that codes for the amino acid carried by the tRNA • Contain a number of modified bases

  36. A “Simple” Gene Transcription Start Site 3’ Untranslated Region 5’ Untranslated Region 5’ Protein Coding Region 3’ RNA Transcript Promoter/ Control Region Terminator Sequence

  37. Transcription Initiation • Proteins called transcription factors bind to the promoter region of a gene • If the appropriate transcription factors are present, RNA polymerase binds to form an initiation complex • RNA polymerase melts the DNA at the transcription start site • Polymerization of RNA begins

  38. Initiation Promoter T. F. RNA Pol. T. F. RNA Pol. RNA 5’ T. F.

  39. Transcription And Translation In Prokaryotes 5’ 3’ 3’ 5’ RNA Pol. Ribosome mRNA Ribosome 5’

  40. Heat Shock Response Elements • Sudden changes in the temperature of cells cause stress in response to which heat shock genes are expressed • At least some heat shock genes are thought to be chaperones that help proteins fold correctly • Heat shock genes have Heat Shock Elements (HSEs) in their control regions • Heat Shock Transcription Factors (HSTFs) bind the HSEs up regulating expression of heat shock gene products

  41. Control of Gene Expression Cytoplasm Nuclear pores Degradation AAAAAA AAAAAA DNA Transcription Modification RNA RNA Processing G G Degradation etc. Ribosome mRNA G AAAAAA Export Translation Nucleus Packaging Transportation

  42. A “Simple” Gene Transcription Start Site 3’ Untranslated Region 5’ Untranslated Region 5’ Protein Coding Region 3’ RNA Transcript Promoter/ Control Region Terminator Sequence

  43. Initiation Promoter T. F. RNA Pol. T. F. RNA Pol. RNA 5’ T. F.

  44. Transcription And Translation In Prokaryotes 5’ 3’ 3’ 5’ RNA Pol. Ribosome mRNA Ribosome 5’

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