Biochem 69

Question 1

What is the function of helicase in DNA replication?

Answer 1

Unwinds DNA template at replication fork

Question 2

What are the functions of single-stranded binding proteins in DNA replications

Answer 2

Prevents strands from reannealing

Question 3

What is the function of DNA topoisomerase (also known as DNA Gyrase)

Answer 3

Create a single or double stranded break in the helix to add or remove supercoils.

Question 4

Which antibiotic inhibits DNA Gyrase (prokayrotic topoisomerase II)?

Answer 4

Fluoroquinolones

Question 5

What is the function of Primase in DNA replication?

Answer 5

Makes an RNA primer on which DNA Polymerase III can initiate replication.

Question 6

What is the function of DNA polymerase III? (3)

Answer 6

1) Elongates leading strand by adding deoxynucleotides to the 3 prime end (so, synthesis 5 ->3)
2) Elongates lagging strand until it reaches primer of preceding fragment.
3) 3-5 prime exonuclease activity “proofreads” each added nucleotide (proofreads 3 -> 5)
note: only in prokaryotes.

Question 7

What is the function of DNA Polymerase I in DNA replication?

Answer 7

1) Degrades RNA primer and replaces with DNA

Note: only in prokaryotes

Question 8

What is the function of DNA ligase in DNA replication?

Answer 8

joins Okazaki fragments through formation of phosphodiester bond

Question 9

What is the function of Telomerase?

Answer 9

An RNA dependent DNA polymerase that adds DNA to 3’ ends of chromosomes to avoid loss of genetic material with every duplication.