MolBio5 - 36

Question 1

What breaks down Ppi into 2Pi?

Answer 1

Pyrophosphatase

Question 2

Why is DNA synthesis said to be irreversible?

Answer 2

It involves the breakdown of Ppi into 2Pi

Question 3

What provides the energy for DNA synthesis?

Answer 3

Breakage of two high energy phosphate bonds

Question 4

What is the energy usage of DNA replication?

Answer 4

-7kCal/mol

Question 5

Describe the direction of DNA synthesis?

Answer 5

Bidirectional

Question 6

What removes the RNA primers of the okazaki fragments?

Answer 6

Ribonuclease H

Question 7

What makes the okazaki fragments continuous?

Answer 7

DNA ligase

Question 8

What are the 9 replication proteins?

Answer 8

Helicase, single-stranded binding proteins, primase, polymerase, sliding clamp, clamp loader, ribonuclease H, ligase and topoisomerase

Question 9

What does ribonuclease H do?

Answer 9

Removes RNA primers

Question 10

What does DNA ligase do?

Answer 10

Uses the energy of ATP hydrolysis to ligate newly synthesise, adjacent DNA fragments in a two-step catalytic reaction

Question 11

Outline the first step of DNA ligase

Answer 11

ATP + 5’-P > P-P + 5’-P-AMP

Question 12

Outline the second step of DNA ligase

Answer 12

P-P > 2Pi + free energy

Question 13

What is the ligation process described as?

Answer 13

Energetically highly favourable

Question 14

What keeps the ligation process energetically highly favourable?

Answer 14

Phyrophosphatase

Question 15

What does DNA primase do?

Answer 15

Synthesis a short RNA primer required by ALL DNA for synthesis initiation

Question 16

What does DNA helicase do?

Answer 16

Uses ATP to separate the parental DNA strands at the replication fork and moves the fork forwards

Question 17

What is DNA helicase activity reliant upon?

Answer 17

ATP and magnesium

Question 18

What can mutations in helicase activity cause?

Answer 18

Progeria, such as Werner Syndrome, resulting in premature aging

Question 19

Describe Werner Syndrome

Answer 19

A form of progeria, mutation are AR in RECQ helicase gene WRN

Question 20

What aids DNA polymerase?

Answer 20

Sliding clamp and clamp loader

Question 21

How do sliding clamp and clamp loader help DNA polymerase?

Answer 21

Sliding clamp is positioned close to the primer:template junction by clamp loader, encircling the DNA like a nut on a bolt to help move the DNA polymerase forwards

Question 22

What do single-stranded binding proteins do?

Answer 22

Expose single-stranded DNA in the replication fork, making it available for templating synthesis of the new DNA strand and easing replication fork progression

Question 23

What do DNA topoisomerases do?

Answer 23

Prevent DNA from becoming tangled during DNA replication

Question 24

How do DNA topoisomerase prevent DNA from becoming tangled?

Answer 24

Nick and reseal the backbone of the parental helix to relieve superhelical tension

Question 25

What do type I topoisomerases do?

Answer 25

Nick and reseal one of the 2 DNA strands, ATP independently

Question 26

What do type II topoisomerases do?

Answer 26

Nick and reseal both of the DNA strands, ATP dependently

Question 27

Describe replication initiation

Answer 27

Biphasic - replicator selection occurs in G1, then origin activation occurs in S phase

Question 28

Outline origin activation

Answer 28

Unwinding of DNA and recruitment of DNA polymerase

Question 29

What is temporal seperation in terms of replication control?

Answer 29

Ensures replicator selection and origin activation are seperated by a fixed amount of time, ensuring each chromosome is only replicated exactly once per cell cycle

Question 30

Outline the mechanism of pre-replicative complex construction

Answer 30

Origin recognition complex (ORC) binds to replicator sequence, helicase loading proteins Cdc6 and Cdt1 binds to ORC, helicase Mcm2-7 binds to complete formation of pre-RC

Question 31

How is the pre-replicative copmlex is controlled?

Answer 31

Low Cdk = pre-RC formation allowed, no activation; high Cdk = no pre-RC formation allowed, pre-RC activation

Question 32

What is the end replication problem?

Answer 32

Need for an RNA primer for initiation of DNA synthesis needs to be removed, but eventually this would lead to chromosome shortening

Question 33

What is added to DNA after replication, and why?

Answer 33

TTAGGG repeats by telomerase to compensate for the loss of telomere sequences caused by RNA primer removal