MGD L1.2 DNA REPLICATION

Question 1

Describe initiation of DNA replication

Answer 1

WHERE DNA REPLICATION BEGINS

BEGINS AT Origin of replication
Origin of replication marked by particular sequence of nucleotides
Iniator proteins bind to origin of replication
This opens DNA double helix by breaking hydrogen bonds
Creates single strand of DNA
The initiator proteins binding + opening up helix attracts other proteins that carry out DNA replication (DNA replication machinery)

Question 2

State where new DNA synthesis occurs

Answer 2

REPLICATION FORKS
Two replication forks formed at each origin of replication
Move from origin in opposite direction , unzipping DNA (bidirectional DNA replication)

Question 3

State DNA replication machinery and their functions

Answer 3

Numbers tell you the order they work in.

5. DNA ligase:
   Joines DNA strands together by catalysing formation of phosphodiester bonds
6. DNA polymerases: Catalyse synthesis of DNA from mono-deoxyribonucleoside triphosphates (dNTPs)
7. DNA helicase: Separates double stranded DNA into single strands allowing each strand to be copied
8. DNA primase: (type of RNA polyemrase): catalises synthesis of short RNA primer complementary to single stranded DNA template (creates short RNA copy complementary to single strand DNA)
9. DNA topoisomerase: unwinds overwound DNA ahead of replication fork (unravels supercoilded structure)

Question 4

Describe elongation in DNA replication

Answer 4

1. New DNA synthesised by DNA polymerase
2. Catalyses addition of nucleotides to free 3’ hydroxyl group on growing DNA strand
3. DNA synthesised in 5’ to 3’ direction