Transcription - Prokaryotes

Question 1

Monocistronic transcripts

Answer 1

Encode one product e.g. containing a singular gene

Question 2

Polycistronic transcripts

Answer 2

Encode more than one product e.g. contains more than 1 gene

Question 3

RNA Polymerase

Answer 3

• Requires a DNA template + nucleoside triphosphate precursors
• Doesn’t require a primer
• Can bind and unwind DNA
• Must know where transcription stops + starts

Question 4

RNA synthesis by RNA polymerase

Answer 4

• Incoming nucleoside triphosphate pairs with the base on the template strand
• Phosphodiester bond is formed and pyrophosphate is released
• RNA-P synthesises RNA in 5’ to 3’ direction, adding nucleotides to 3’ chain

Question 5

During Transcription…

Answer 5

17 bp of DNA are unwound
12 nucleotides form a heteroduplex (DNA-RNA hybrid)

Question 6

The events of transcription - 3 events

Answer 6

Initiation, Elongation, Termination
- DNA sequence contains info that tells RNA polymerase where to initiate and terminate transcription
- Template ‘punctuated’ with start + stop signals

Question 7

Promoters

Answer 7

The ‘start’ signal
- DNA sequence upstream from the transcription start that RNA-P recognises
- Binds other proteins like transcription factors
- RNA-P bind to promoter to initiate transcription
- No primer requires

Question 8

Termination of transcription

Answer 8

The ‘stop’ signal
- Where the new RNA product is released + RNA polymerase dissociated from DNA