Bacterial transcription steps

Question 1

Initiation summary

Answer 1

Locking of holoenzyme onto promoter and the coiling of the DNA to create RNA strand.

Question 1

Initiation step 1

Answer 1

• RNA polymerase moves to promoter region.
• Sigma subunit attaches and binds at -35 and -10 sequences -> polymerase is made into a holoenzyme.

Question 2

Imitation step 2

Answer 2

• Polymerase pulls DNA towards itself.
• DNA is scrunched
• Sigma = still locked on so initiation is difficult.
• Sigma eventually lets go of promoter.

Question 3

Initiation step 3

Answer 3

• -10 region opens
• Closed complex promoter -> open complex promoter.

Question 4

Initiation step 4

Answer 4

• 12-15 bp in unwound region from -10 to +2/+3
• RNA polymerase moved forward so sigma moves away from polymerase
• Polymerase reaches the +1 site and makes copy of template strand.
• Sigma factor is recycled and RNA copy of template forms.

Question 5

Elongation overview

Answer 5

Making longer copy of the template strand

Question 6

Elongation step

Answer 6

• As pol moves over the DNA it unwinds the double strand
• The DNA rewinds after the polymerase has moved on.
• Acts as a proof-reading step
• Can add a base and remove it if it is wrong etc but slower than DNA.

Question 7

2 mechanisms of termination

Answer 7

1) rho-independent
2) rho-dependent

Question 8

Rho-independent mechanism