Basics of DNA Replication

Question 1

Proteins (4)

Answer 1

1) DNA helicase - breaks hydrogen bonds between DNA strands to initiate DNA replication
2) DNA polymerase - synthesizes new DNA strand in 5’ to 3’ direction (needs primer)
3) Topoisomerase II - removes positive supercoiling generated by helicase
4) Primase - synthesizes RNA primers to give DNA polymerase a 3’ OH

Question 2

Leading strand

Answer 2

DNA strand synthesized in the same direction as replication fork; made continuously in 5’ to 3’ direction

Question 3

Lagging strand

Answer 3

Synthesized in segments called Okazaki fragments discontinuously

Question 4

Origin of replication

Answer 4

Location in chromosome where DNA replication initiates; 1 in circular chromosome in cytoplasm of pro cells; thousands in euk cells to increase speed of replication

Question 5

Bidirectional replication

Answer 5

DNA is replicated in both directions at ORI; 2 forks, 2 leading strands, 2 lagging strands; occurs in both PRO and EUK

Question 6

Nick translation

Answer 6

DNA pol I; concurrent 5’ to 3’ excision of RNA nucleotides and DNA polymerization; once all RNA primers replaced, DNA ligase seals nicks in DNA backbone, which can only join two deoxyribonucleotides