L12 - Prokaryotic gene expression 1

Question 1

difference in timing of transcription in pro and eu due to compartmentalisation

Answer 1

prokaryotes undergo transcription and translation at the same time

= fast rproduction of proteins
= needed for immediate transcriptional reponses due to changes in environment

Question 2

what is needed to maintain a population of mRNA in a cell

Answer 2

multiple rounds of transcription of same gene

= due to RNA being unstable and degraded

Question 3

why is transcription dynamic

Answer 3

different affinitys of promoters

= differennce in timing for polymerases to bind to promoter

a gene may have a polymerase bidn as soon as one leaves
= other gene may take much longer

Question 4

how can cells control transcription AFTER initiation

Answer 4

controllable terminator sequnce

= active = mRNA produced is low

antitermination or attenuation allow RNA polymerase to bypass

Question 5

what is bacterial RNA polymerase made of

Answer 5

core RNA polymerase + sigma unit

= specificity = binds to specific promoters

holoenzyme = when core ascociates with sigma unit

Question 6

describe the sigma cycle

Answer 6

sigma unit is what recognises different promoters

= after binding + transcription of 15 bases
= sigma unit is removed

polymnerase continues and sigma unit binds to a new polymerase

Question 7

kd vs K2

Answer 7

Kd is the binding affinity

K2 is the speed of isomerisation/opening of D-loop for transcription

Question 8

which is reversible and which is not - K2 and kd

Answer 8

Kd is reversible

K2 is not

= a strong promoter will have a low Kd and a high K2

Question 9

simple steps in transcription initiation of prokaryotes

Answer 9

1. sigma subunit binds to specifc sequnce/promoter on DNA with RNA polymerase
2. forms closed complex and ismersies

= d loop opened

3. begins transcription

Question 10

why do RNA polymerses not require helicases for transcription in prokaryotes

Answer 10

adenine-thymine rich regions only have 2 hydrogen bonds between them

= ‘breathe’
= open and closing of strands allows sigma subunit to capture strand

Question 11

what positions does sigma subunit bind to and how in transcription

Answer 11

R4 region binds to -35

R2 binds to -10

= in promoter

core polymerase goes from -35 to +1
the entire complex goes from -50 to +20