DNA Replication

Question 1

Where does DNA replication in prokaryotes start?

Answer 1

Starts at origin of replication (oriC):
1) 245 bp
2) 3 A-T rich 13 bp sites
3) 5 DNA binding sites (recognition)

Question 2

First step of DNA replication:

Answer 2

DnaA binds to 1 of 5 recognition sites at oriC

Question 3

Second step of DNA replication:

Answer 3

DnaB (helicase) uses ATP to open and unwind helix at the A-T rich 13-bp sites

Question 4

Third step of DNA replication:

Answer 4

Single-strand binding (SSB) proteins prevent reformation of double helix by binding to single-stranded DNA

Question 5

Fourth step of DNA replication:

Answer 5

Primase (RNA polymerase) synthesizes a primer, or 10-bp starting block, complementary to template strand; primer determines starting point of DNA replication

Question 6

Fifth step of DNA replication:

Answer 6

1) Topoisomerases uncoil DNA by cutting, unwinding, then rejoining
2) Type II topoisomerase is for double stranded DNA, requires ATP
3) Type I topoisomerase is for single stranded DNA, does NOT require ATP

Question 7

Sixth step of DNA replication:

Answer 7

1) DNA Polymerase III adds dNTPs (dATP, dCTP, dGTP, and dTTP) with co-factor Mg2+ onto 3’-OH end (replication is unidirectional, occurs 5’ to 3’)
2) Requires primer and template
3) Also has exonuclease function that checks bases from 3’ to 5’ and repairs as necessary
4) Forms leading strand (continuous) and lagging strand (fragmented), both in 5’ to 3’ direction

Question 8

Seventh step of DNA replication:

Answer 8

1) DNA Polymerase I: uses polymerase function in 5’ to 3’ direction for replication
2) uses exonuclease function in 5’ to 3’ direction for primer removal
3) uses exonuclease function in 3’ to 5’ direction for repair

Question 9

Eighth (final )step of DNA replication:

Answer 9

DNA ligase seals “nicks” and connects Okazaki fragments