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Lent Module 2 Transcription in prokaryotes with 100- correct answers
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Lent Module 2 Transcription in prokaryotes with 100- correct answers
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Lent Module 2:Transcription in
prokaryotes with
100% correct answers
Gene
A sequence of genomic DNA that encodes a single
functional RNA.
Why are prokaryotes able to change their gene expression
so quickly?
- No nucleus
- No introns
- Operons (a number of genes linked together and
controlled by a single promoter)
- Co-transcription (mRNA is translated whilst still being
transcribed)
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Polycistronic transcripts
mRNA generated from an operon which encodes several
different polypeptides.
Features of transcription
- Occurs in the 5'-3' direction.
- Only one strand is copied, the coding strand. Different
strands may be copied in different regions of DNA.
- Occurs in discrete units (the length of the RNA chain is
between <100->10000nt). Defined stopping and starting
points.
Prokaryotic RNA polymerase
- One RNA polymerase synthesises all RNA - mRNA, rRNA
and tRNA.
- Higher error frequency than DNA replication as no proof-
reading 3'-5' exonuclease activity.
- Two different forms: core enzyme and holoenzyme
RNA polymerase core enzyme and holoenzyme
Enzyme is asymmetric.
- Core enzyme binds DNA randomly on either strand.
- Additional sigma subunit on the holoenzyme binds to
allow recognition of gene promoter regions.
Requirements for RNA polymerase
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