DNA Replication

Question 1

Replication

Answer 1

Process of which a cell copies its DNA before divison

Question 2

Replication must be?

Answer 2

Rapid and accurate

Question 3

What model is used for DNA Replication?

Answer 3

The semiconservative model, each DNA strand serves as a template for the synthesis of new DNA strand

Question 4

What is the polarity of the template and new strand of DNA?

Answer 4

New strand = 5’-3’
Template strand 3’-5’

Question 5

What are the requirements for DNA replication?

Answer 5

1. Template (single standed DNA)
2. Raw materials (DNA triphosphates-dNTPs) to be assembled into a new nucleotide strand
3. Enzymes and other proteins (read the template and assemble the substrates into a DNA molecule)
4. Primer (short segment of nucleotides(RNA) bound to the template strand. acts as a substrate for DNA polymerase)

Question 6

What enzymes are present in DNA replication and what is there function?

Answer 6

1. Helicase: untwists the DNA
2. Primase: constructs RNA primer
3. DNA polymerases: polymerization of nucleotide precursors into DNA Chain (5’-3’) and finds the correct nucleotide to pair with nucleotide on template strand

Question 7

What happens at the site of replication?

Answer 7

Starts at the replication origin
forms a replication bubble that unwinds the helix at the replication fork

Question 8

How does DNA replication begin?

Answer 8

When the initiator proteins bind to the origin of replication

Question 9

What happens during the initiation of replication?

Answer 9

1. Initiator proteins bind to replication origin
2. DNA helicase binds to the initiator proteins
3. Helicase loads onto DNA
4. Helicase denatures helix and binds DNA primase to form primosome
5. Primase synthesizes RNA primer, which is extended as DNA chain by DNA polymerase

Question 10

What is the polarity of a discontinuous strand of DNA?

Answer 10

5’-3’

Question 11

What is the polarity of a continuous stand of DNA?

Answer 11

3’-5’

Question 12

What are the steps of Semidiscontinuous Replication?

Answer 12

1. Initiation, RNA primer made by DNA primase and starts replication of the lagging strand (1st okazaki fragment synthesis)
2. Further untwisting and elongation of new DNA strands (2nd okazaki fragment elongated)
3. Process continues, 2nd okazaki fragment finished and 3rd being synthesized; DNA primase beginning 4th fragment.
4. Primer removed by DNA polymerase 1 (Replaces RNA primer with DNA)
5. Joining of adjacent DNA fragments by DNA ligase. (glues okasaki fragments together)

Question 13

Leading Strand

Answer 13

Continuous replication of DNA
5’-3’ —–>

Question 14

Lagging Strand

Answer 14

Discontinuous replication of DNA
3’-5’ ——>
Okazaki fragments

Question 15

Template Strand

Answer 15

Stand which new DNA strand is synthesized according to complementary base-pairing rules

Question 16

What is the process of fixing mistakes made during replication?

Answer 16

1 mistake per billion nucleotides because polymerases are very accurate.
1. Proofreading: if an incorrect base is added the polymerase is stalled and removes the incorrect base and replaces it with the correct one
2. Mismatched repair: if proofreading fails the repair enzymes recognize the deformity in the secondary structure and replace it with the correct one.

Question 17

What are the functions of DNA polymerase I, II, III?

Answer 17

I: Removes and replaces primers
II: DNA repair (not in exonuclease 5’-3’)
III: Elongates DNA (not in exonuclease 5’-3’)