DNA replication

Question 1

whats semi conservative DNA

Answer 1

when replicated, dsDNA = 2x ( parent + new antiparallel strand )

Question 2

whats conservative DNA

Answer 2

when replicated, one dsDNA is the same, and one is completely new - synthesised complementarily to parent

Question 3

whats dispersive DNA

Answer 3

daughter DNA contains parental and newly synthesised DNA

Question 4

describe Meselson Stahl experiment

Answer 4

e coli grown in 15N mediul
this was added to 14N medium, so any newly synthesised DNA would contain 14N
separated in centrifuge - more dense (15N) at bottom, less dense at top.

Question 5

what is the position where the DNA helix is unwinded called

Answer 5

replication origin

Question 6

how many replication origins do cprokaryotic and eukaryotic chromosomes have?

Answer 6

1, multiple

Question 7

describe regulation of prokaryotic origin of replication

Answer 7

highly regulated - only opened when A’s are methylated and when sufficient nutrients are available

Question 8

describe first steps of dna rep (hint: helicase and ssBP)

Answer 8

1. DNA helicase opens DNA helix
   • DNA helicase hydrolyses ATP; harnesses this energy to pry apart 2 strands.
2. ssBP keeps strands separate, but keeps bases exposed

Question 9

describe what happens after ssBP but before DNA p

Answer 9

3. DNA primase synthesises RNA primer
4. Sliding clamp and clamp loader bind together
5. complex binds to RNA primer
6. DNA p binds to primer and complex
7. Clamp loader dissociates

Question 10

describe how DNA p works

Answer 10

8. DNAp reads the template strand in 3’5’ direction
9. DNAp forms 5’3’ complementary DNA strand
   • DNAp has fingers, which recognise the other strand’s base, and adds the complementary base.
   • DNAp hydrolyses nucleoside triphosphates into nucleoside monophosphates – first pyrophosphate is formed, then 2x phosphate groups
   • DNAp catalyses condensation between 3’ OH and OH of 5’ phosphate

Question 11

what happens to RNA primer when polymer is synthesised

Answer 11

RNase H degrades it. DNA replaces the primer

Question 12

describe the action of DNA polymerase.

Answer 12

shaped like a hand - groove determines what complementary dNTP to add.
enzyme hydrolyses dnTP to nucleotides and pyrophosphate, enabling addition to the 3’ end.

Question 13

the half of the strand closest to the 5’ end of template is called the

Answer 13

leading strand

Question 14

the half of the strand closest tothe 3’ end of the template strand is called the

Answer 14

lagging strand

Question 15

whats special about lagging strand?

Answer 15

grows via okazaki fragments

they are separated, and joined by ligase