Prokaryotic transcription

    Cards (11)

    • Bacteria are concerned about survival and energy efficiency and this shapes genome size
    • Analysing the genome tells us what could happen – analysing the transcriptome, proteome or metabolome begins to help us understand what is happening!
    • Bacterial structural gene and its mRNA product
      • Promoter: Binding site for RNA polymerase, not transcribed or translated, orients RNA polymerase
      • Transcription start site (+1): First nucleotide in mRNA, may not be translated
      • Leader: Can be important in regulation of transcription and translation, includes Shine-Dalgarno sequence
      • Coding region: Starts with start codon, ends with stop codon
      • Trailer: Transcribed but not translated, prepares RNA pol for release
      • Terminator: Signals RNA pol to stop transcription
    • Many genes with similar functions are grouped together in bacteria, transcribed from a single promoter, called an operon
    • Polycistronic mRNA
      Contains multiple protein synthesis initiation sites, leads to multiple proteins, efficient mechanism to control production of proteins with related functions
    • RNA Polymerase
      • Central to transcription in bacteria, single enzyme unlike eukaryotes
      • Sigma factor: Helps core enzyme recognise promoter, forms 'holoenzyme'
    • Bacterial Transcription Cycle
      1. Initiation
      2. Elongation
      3. Termination
    • Sigma factor
      Critical to initiation process, positions RNA polymerase at promoter, recognises consensus sequences
    • Steps in transcription by bacterial RNA polymerase
      1. Initiation: Locates and binds to promoter, breaks DNA duplex, forms channel for template DNA
      2. Elongation: Core RNAP moves along template, new RNA strand synthesized 5' to 3'
      3. Termination: Core RNAP dissociates from template DNA, can be factor dependent or independent
    • Transcription termination - two types: factor dependent or independent
    • Rho-factor dependent termination of transcription
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