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Promoter sequences from 10 bacteriophage and bacterial genes - PowerPoint PPT Presentation


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Promoter sequences from 10 bacteriophage and bacterial genes. Figure 10-13 Catabolite control of the lac operon. (a) Only under conditions of low glucose is adenylate cyclase active and cAMP (cyclic adenosine monophosphate) formed. (b) When cAMP is present, it forms a complex with CAP

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slide5

Figure 10-13 Catabolite control of the lac operon. (a) Only

under conditions of low glucose is adenylate cyclase active

and cAMP (cyclic adenosine monophosphate) formed.

(b) When cAMP is present, it forms a complex with CAP

(catabolite activator protein) that activates transcription by

binding to a region within the lac promoter.

slide7

NEGATIVE REGULATION

REPRESSIBLE TRANSCRIPTION

THE trp OPERON

Aporepressor

Operator

Co-repressor

Active repressor

X

slide12

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rna polymerase transcribing a prokaryotic gene
RNA Polymerase Transcribing a Prokaryotic Gene
  • Initiation occurs at a transcription start site in a promoter (DNA sequence)
  • Termination occurs at a transcription stop site
  • Activation of bacterial RNA polymerase requires binding of sigma factor
slide14

Transcription in Eukaryotes

Eukaryotic RNA Polymerases

  • Three different RNA polymerases transcribe nuclear genes
  • Other RNA polymerases found in mitochondria and chloroplasts
slide15

Eukaryotic vs. Prokaryotic Transcription

  • In eukaryotes, transcription and translation occur in separate compartments.
  • In bacteria, mRNA is polycistronic; in eukaryotes, mRNA is usually monocistronic.
    • Polycistronic: one mRNA codes for more than one polypeptide
    • moncistronic: one mRNA codes for only one polypeptide
  • 3 RNA polymerases in euk., 1 in prok.
  • Binding of Basal Transcription Factors required for euk. RNA Pol II binding.
  • “Processing” of mRNA in eukaryotes, no processing in prokaryotes
slide22

TERMINATION

  • RNA polymerase meets the terminator
    • Terminator sequence: AAUAAA
  • RNA polymerase releases from DNA
    • Prokaryotes-releases at termination signal
    • Eukaryotes-releases 10-35 base pairs after termination signal