DNA Replication 1

Question 1

What are the three rules of DNA replication?

Answer 1

• It is semiconservative
• replication beings at an origin and proceeds bidirectionally
• Synthesis proceeds in a 5’—>3’ direction and is semidiscontinuous

Question 2

What does semiconservative replication mean?

Answer 2

Each daughter duplex consists of one parental strand and one newly synthesized strand.

The parental strand is used as a template for the synthesis of the new strand.

Question 3

What are origins of replication?

Answer 3

Unique sites at which replication begins that are rich in AT base pairs.

Question 4

What initiates DNA synthesis?

Answer 4

An RNA primer

Question 5

What is the name of the strand that is synthesized continuously? Discontinuously?

Answer 5

Leading strand is continuous

Lagging strand is discontinuous

Question 6

What is the function of AAA+ ATPase (DnaA)?

Answer 6

Binds to the origin of replication and dissociates the strands utilizing ATP hydrolyzation.

Question 7

What is the function of DNA Ligase?

Answer 7

Creates phosphodiester bonds utilizing ATP, seals “nicks” in the DNA strand

Question 8

What is the role of DNA polymerase?

Answer 8

Group of enzymes that are responsible for strand elongation, require a ssDNA for a template and an RNA primer

Question 9

What is the function of helicase?

Answer 9

Unwinds the double helix utilizing ATP

Question 10

What is the function of nucleases?

Answer 10

Sever phosphodiester bonds of the DNA backbone, can be endo- or exo-

Question 11

What is the function of primase?

Answer 11

Synthesizes short stretches of RNA complementary to the template DNA strand that serve as a primer for DNA polymerase

Question 12

What is the function of topoisomerase?

Answer 12

Adjust the supercoiling of DNA double helices to alleviate supercoiling stress and introduce negative supercoiling.

Contain both endonuclease and ligase function

Question 13

What are the three steps of DNA synthesis?

Answer 13

Initiation

Elongation

Termination

Question 14

What happens during initiation?

Answer 14

DNAa binds the origin of replication

Helicase dissociates the double helix

SsDNA binding proteins protect DNA and maintains dissociation

Question 15

How is the leading strand synthesized?

Answer 15

DNA polymerase III synthesizes the strand in the 5’—>3’ direction, starting at the 3’ end of an RNA primer.

Synthesized continuously

Question 16

How is the lagging strand synthesized?

Answer 16

Discontinuously as a series of small fragments (Okazaki fragments) by DNA polymerase III.

Still made in the 5’—>3’ direction

Question 17

What is DNA gyrase and what is its function?

Answer 17

A type II topoisomerase that alleviates positive supercoiling imposed by strand unwinding

Question 18

How are mismatches identified in DNA proofreading and how are they corrected?

Answer 18

The number of rings and the hydrogen bonding pattern.

If these aren’t correct, DNA polymerase uses its 3’—>5’ exonuclease activity to excise the mismatched nucleotide

Question 19

What happens during termination?

Answer 19

DNA gyrase resolves the two newly formed chromosomes

Question 20

What are the three mechanisms that ensure replication fidelity?

Answer 20

Geometry of the active site of DNA polymerase

Proofreading: 3’—>5’ exonuclease activity

Mismatch repair and DNA methylation

Question 21

How does DNA methylation ensure replication fidelity?

Answer 21

The parent strand is methylated so that the cell can tell which strand should be used to correct mistakes

Question 22

What is the function of DNA polymerase I?

Answer 22

DNA repair and removes RNA primers during replication

Question 23

Function of DNA Pol II?

Answer 23

DNA repair

Question 24

Function of DNA pol III?

Answer 24

Synthesizes most of the DNA on both leading and lagging strands

Question 25

Function of DNA pol IV and V?

Answer 25

DNA repair functions