dna replication 1

Question 1

what enzyme is required in bacterial cells for DNA synthesis

Answer 1

DNA polymerase III

Question 2

which direction do bacterial polymerases synthesise

Answer 2

5’ —-> 3’

Question 3

how do we know if a gene is important

Answer 3

simple knock-outs will be lethal, meaning the replication cannot occur

Question 4

what is a quick-stop mutant

Answer 4

where the inactivated gene will stop replication immediately

Question 5

what is a slow-stop mutant

Answer 5

the current round of replication will finish but a new one cannot start

Question 6

what does plectonemically coiled mean

Answer 6

where the dna strands are wrapped around eachother

Question 7

what do we use to unwind the dna duplex and what is the process called

Answer 7

helicase
atp hydrolysis

Question 8

how does helicase work

Answer 8

a conformational change occurs in the helicase and these pull on the DNA strand and separate it

Question 9

what direction do helicases move in

Answer 9

3’

Question 10

what can unwinding the duplex cause and what does this lead to

Answer 10

it can cause torsional strain
supercoiling

Question 11

what will the writhe be when the DNA is in its relaxed form

Answer 11

0

Question 12

if the linking number is bigger than the relaxed form, what does this mean

Answer 12

there is positive supercoling

Question 13

if the linking number is smaller than in the relaxed form, what does this mean?

Answer 13

there is negative supercoiling

Question 14

what does writhe do

Answer 14

it releases tension from supercoiling

Question 15

if the dna is wound to the right, what does it make the DNA and heat does this mean for the type of winding

Answer 15

negative
underwound

Question 16

if the dna is wound to the left, what does it make the DNA and heat does this mean for the type of winding

Answer 16

positive
overwound

Question 17

what will the supercoiling value be for purified cellular dna

Answer 17

-0.06

Question 18

what will the supercoiling value be for purified cellular DNA and why is this

Answer 18

-0.06
makes it easier to separate when replicating

Question 19

when will dna in eukaryotes be underwound and what does it form

Answer 19

around histones
a nucleosome

Question 20

when will positive supercoiling occur and why does this happen

Answer 20

during helicase bases unwinding as it causes overwinding elsewhere a the linking number wont be able to release the stress without breaking bonds

Question 20

when will positive supercoiling occur and why does this happen
( 2 occasions )

Answer 20

-during helicase bases unwinding as it causes overwinding elsewhere the linking number won’t be able to release the stress without breaking bonds
-long linear DNA as it causes local overwinding

Question 21

what is the problem with positive supercoiling

Answer 21

it needs to be removed for replication to continue

Question 22

what enzymes remove supercoils and what do the two types do

Answer 22

topoisomerases
- type 1 cleaves 1 backbone strand
-type 2 cleaved both backbone strands

Question 23

how does type 1 work and how does it affect the linking number

Answer 23

-the DNA backbone transfers to the enzyme via tyrosine residue and then transferred back when it is unwound
- increases the Lk by 1

Question 24

what does type 1 do

Answer 24

stops the dna from becoming too unwound