dna replication

Question 1

in which direction does dna replication occur in?

Answer 1

5’ to 3’

Question 2

what provides the free energy of required for dna synthesis?

Answer 2

breaking of 2 high energy phosphate bonds in pyrophosphate

Question 3

DNA ligase

Answer 3

uses energy from ATP hydrolysis to form phosphodiester bond between 2 DNA fragments

Question 4

Werner syndrome

Answer 4

• mutation in WRN gene —> codes for RECQ helicase
• autosomal recessive
• progeria = premature aging
  cell death due to defective dna replication during growth and regeneration

Question 5

Bloom syndrome

Answer 5

LOF mutation in RECQ dna helicase - involved in dna repair

cancer

Question 6

sliding clamp

Answer 6

1. clamp loader uses energy from atp hydrolysis to load sliding clamp onto primer-template junction
2. sliding clamp fixes dna polymerase to primer-template junction + moves it forward

Question 7

what is the human sliding clamp?

Answer 7

PCNA

Question 8

single stranded binding proteins (SSBs)

Answer 8

bind to DNA strand + keeps replication fork open and prevents hairpins
cooperatively binds
makes DNA strand readily available to DNA polymerase

Question 9

DNA topoisomerases

Answer 9

makes either a double stranded or single stranded nick and reseal to release superhelical tension as a result of supercoils formed by parental DNA in front of replication fork
breaks and reforms phosphodiester bond

Question 10

replicator origin

Answer 10

sequence where DNA replication begins

Question 11

what is the yeast replicating origin?

Answer 11

ARS

Question 12

what is the human replicating origin?

Answer 12

HBB, LMNB2, MYC

Question 13

describe the process of the initiation of dna replication

Answer 13

1. g1 phase
   - ORC binds to replicator origin sequence
   - helicases cdc6 and cdt1 bind to ORC
   - helicase mcm2-7 binds
   - pre-replicative complex formed
   - low cdk levels
2. s phase
   - dna unwinds and recruits dna polymerase
   - high cdk levels activates existing pre-rc but prevents new pre-rcs from forming

Question 14

the 5’ end of the lagging strand shortens progressively. why is this the case?

Answer 14

removal of rna primer by ribonuclease H at end of dna replication leaves a gap

Question 15

telomerase

Answer 15

ribonucleoprotein containing rna template used to synthesise TTAGGG repeats on 3’ end of parental DNA strand in a step wise process = telomerase shuffle
additional 3’ end = template for new okazaki fragment