transcription 2

Question 1

what is an operon

Answer 1

a section of genes encoding for proteins related to each other, they are located adjacently and controlled as a single unit

Question 2

within the promotor region of dna in prokaryotes, what are the 2 consensus DNA sequences and where are they located

Answer 2

• hexamer at -35 bps
• Pribnow box at -10 bps

Question 3

what is a feature of the consensus DNA sequences and why does it have it

Answer 3

it is only in one dna strand so the polymerase knows which way to go

Question 4

what are down mutations

Answer 4

mutations that decrease the promoter initiation and decrease the conformity to the consensus sequence

Question 5

what is an up mutation

Answer 5

a mutation that can trigger transcription initiation

Question 6

what are the other 3 bacterial promoters

Answer 6

up, extended and discriminator

Question 7

what is a holoenzyme

Answer 7

an enzyme and a coenzyme

Question 8

what are the 4 subunits of rna polymerase and what are their functions

Answer 8

• 2 alpha units for enzyme assembly
• beta and beta prime unit forms the catalytic centre
• sigma unit binds to promoter

Question 9

why does the polymerase need the sigma region

Answer 9

it has strong binding strength for dna

Question 10

what is sigma 70 used for

Answer 10

general use

Question 11

what is sigma 32 induced by and what is different about it

Answer 11

high temperatures
will recognise different consensus regions

Question 11

what is sigma 32 induced by and what is different about it

Answer 11

high temperatures
will recognise different consensus regions

Question 12

what is sigma 54 induced by

Answer 12

lack of nitrogen

Question 13

how can transcription be negatively regulated

Answer 13

repressors which bind to an operator site, which stops polymerase from binding

Question 14

how can transcription be positively regulated

Answer 14

activators bind to a specific site and help polymerase bind

Question 15

whats the repressor and activator of the lac operon

Answer 15

lac repressor and CAP-activating protein

Question 16

what does beta-galactosidase do and what gene encodes for it

Answer 16

cleaves lactose into component sugars
lacZ

Question 17

what does permease do and what gene encodes for it

Answer 17

transports lactose into cell
lacY

Question 18

what does transacetylase do and what gene encodes for it

Answer 18

modifies lactose
lacA

Question 19

what is lacI

Answer 19

regulatory gene

Question 20

what happens in the lac operon when lactose is absent

Answer 20

the repressor is produced and it is bound to the operator site

Question 21

what happens to the lac operon when lactose is present

Answer 21

allolactose will bind to the lac repressor and this will induce a conformational change in lacI so the repressor will not bind to the operator

Question 22

what part of the lac repressor binds to the operator site and where

Answer 22

the lac repressors 2 dimers each bind to one operator site

Question 23

how many operator sites does the lac operon have and which 2 can repressors bind to (2 lots of pairs)

Answer 23

3
-O1 and O2
-O1 and O3

Question 24

what happens within the lac operon when glucose is low

Answer 24

cAMP will increase and this will activate CAP, meaning polymerase affinity will increase

Question 24

what happens within the lac operon when glucose is high

Answer 24

cAMP will decrease and this means CAP is inactive, meaning polymerase not bind and the lac operon will not be activated

Question 25

what is lactose converted to

Answer 25

allolactose

Question 26

if there is low lactose and low glucose what will happen to the lac operon

Answer 26

there will be no transcription

Question 27

how do we terminate transcription

Answer 27

there are 2 sections of symmetric dna and an A-T this forms the stem and loop structure which stalls the polymerase the A-T(U) region is weakly bonded so will cause unravelling

Question 28

what is rho and what is rho-dependent termination

Answer 28

rho is a prokaryotic transcription protein it will attach and move along the rna via atp hydrolysis and when the rna is stalled by the stem and loop, it will catch up and unwind the RNA-DNA pairing