Ecclesiastes 3:1

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• Ecclesiastes 31
• 1 To every thing there is a season, and a time to
  every purpose under the heaven

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TranscriptionConcentrating on Prokaryotes

• Timothy G. Standish, Ph. D.

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All Genes Cant 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.

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Logical Expression Control Points

• 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
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IntroductionThe Central Dogma of Molecular
Biology
Cell
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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

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General Model For Transcription
RNA Polymerase
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General Model For Transcription
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General Model For Transcription
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General Model For Transcription
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General Model For Transcription
Top- Isomerase I
Gyrase
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General Model For Transcription
Top- Isomerase I
Gyrase
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General Model For Transcription
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General Model For Transcription
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General Model For Transcription
Ribosome
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General Model For Transcription
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General Model For Transcription
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General Model For Transcription
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General Model For Transcription
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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

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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

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Prokaryotic Transcription Initiation
RNA Pol.
??
Constitutive Gene
Heat Shock Gene
P1
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Prokaryotic Transcription Initiation
RNA Pol.
??
Constitutive Gene
Heat Shock Gene
P2
P1
Different promoters
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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

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TerminationRho Independent
Terminator
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TerminationRho Independent
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TerminationRho Dependent
The terminator sequence slows RNA polymerase
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TerminationRho Dependent
Rho catches up with RNA polymerase
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TerminationRho Dependent
The elongation complex disintegrates
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(No Transcript)
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Transcription
Coding (sense) strand
3
5
5
3
Template (antisense) strand
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Transcription
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Transcription
Coding (sense) strand
3
5
5
3
Template (antisense) strand
5
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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

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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

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A Simple Gene
Transcription Start Site
3 Untranslated Region
5 Untranslated Region
Protein Coding Region
3
5
RNA Transcript
Terminator Sequence
Promoter/ Control Region
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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

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Initiation
T. F.
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Transcription And Translation In Prokaryotes
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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

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(No Transcript)
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Control of Gene Expression
Packaging
Transportation
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A Simple Gene
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Initiation
T. F.
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Transcription And Translation In Prokaryotes