DNA Replication

Question 1

Name the enzyme responsible for repairing single-stranded breaks in dsDNA.

Answer 1

DNA ligase

Question 2

What are the functions of DNA polymerase I, and III, respectively?

Answer 2

DNA polymerase I functions to replace RNA primers with DNA segments using its 5’ –> 3’ exonuclease activity.

DNA polymerase III is the primary enzyme for synthesizing daughter DNA strands (but cannot remove the RNA primer).

Question 3

Which enzyme is responsible for unwinding DNA at the replication fork? Which enzyme is responsible for relieving supercoiling resulting from replication fork unwinding?

Answer 3

Helicase unwinds DNA at the fork.

Gyrase/topoisomerase type II relieves supercoiling strain.

Question 4

Describe the process of how a cell corrects spontaneous deamination of cytosine -> uracil.

Answer 4

Glycosylase cleaves out the uracil leaving an apurinic/apyrimidinic site.

An AP (apurinic/apyrimidinic) endonuclease cleaves the phosphate backbone on the 5’ end and lyase cleaves the 3’ end of the abasic site.

DNA polymerase inserts the correct nucleotide.

Ligase seals the nick.

Question 5

What is the function of helicase in DNA replication?

Answer 5

It acts at the replication fork to unwind and separate the DNA.

Question 6

Fill it out b.

Answer 6