6.4 DNA replication

Question 1

What does unwinding of the DNA double helix do

Answer 1

It exposes the bases on each strand

Question 2

Each strand can act as a ________ for the synthesis of new strands

Answer 2

template

Question 3

New strand forms by __________ of complementary base pair

Answer 3

insertion

Question 4

1 DNA molecule yields ___________ at the end of DNA replication

Answer 4

Two identical daughter double stranded DNA molecules

Question 5

What are the three possible models of DNA replication

Answer 5

Semiconservative, Conservative, Dispersive

Question 6

Who discovered the semiconservative model

Answer 6

Watson and Crick

Question 7

Explain the conservative model

Answer 7

The parental double helix remians intact, and both strands of each of the two daughter helices are newly synthesised.

Question 8

Explain the dispersive model

Answer 8

Both strands of both daughter helices contain original and newly synthesised DNA

Question 9

What is the aim of the Meselson-Stahl experiment

Answer 9

to determine which of three models accurately describes DNA replication.

Question 9

Explain the Semicoservative model

Answer 9

This model proposed that each DNA strand serves as a template for a new strand, resulting in daughter DNA molecules containing one original and one newly synthesized strand.

Question 10

Where does the energy for DNA replication come from?

Answer 10

It comes from high-energy phosphate bonds associated with dNTPs

Question 11

What is the function of DNA polymerase

Answer 11

It catalyses new phosphodiester bonds

Question 12

What are the two steps of DNA replciation

Answer 12

Initiation and Elongation

Question 13

What occurs during Initiation

Answer 13

Proteins open up the double helix and prepare it for complementary base pairing

Question 14

What occurs during elongation

Answer 14

proteins connects the correct sequence of nulceotides on newly formed DNA strands (correctly copied from the template strand)

Question 15

Which direction does DNA replication proceed

Answer 15

In the 5’ to 3’ direction

Question 16

DNA polymerase adds nucleotides to the ____of the new strand

Answer 16

3’-OH

Question 17

What are the three requirements for DNA polymerase action

Answer 17

1. four dNTPs for: incorporation into chain and energy
2. Single-stranded template: may be unwound by other proteins
3. Primer with exposed 3’ hydroxyl

Question 18

What do the enzymes/proteins do during initiation

Answer 18

initiator protein: binds to the origin of replication
DNA helicase: unwinds the helix
single-stranded binding proteins: Keep the DNA helix open and prevent it from winding up again
Primase: it synthesises RNA primers

Question 19

primers are…….

Answer 19

complementary and antiparallel to each template strand.

Question 20

What do the proteins/enzymes do during elongation

Answer 20

DNA polymerase III: catalyses phosphodiester bond formation between adjacent nucleotides (polymerization)
DNA polymerase I: fills in the gaps between the newly synthesised okazaki fragments on the laggin strand

Question 21

differentiate between the leading strand, lagging strand and okazaki fragments

Answer 21

leading strand- it has continuous synthesis
laggind strand- has discontinous synthesis
Okazaki fragments- short DNA fragments on the lagging strand

Question 22

The DNA replication of a circular bacterial chromosome is:

Answer 22

bidirectional

Question 23

Outline the steps of circular bacterial chromsome DNA replication

Answer 23

1.There is only 1 origin of replication
2.Two forms moving in opposite directions, meeting at a designated termination region
3.Unwinding distorts the DNA molecule creating supercoiled DNA ahead of the replication fork
4.DNA topoisomerase relaxes supercoils by breaking, unwindING and suturing the DNA
5.DNA topoisomerase cuts DNA
6.Cut strands rotate to unwind
7.Cut ends are re-joined by ligase
8.Replication is complete when replication forks meet at the termination region
8.Topoisomerases separate entwined daughter chromosomes

Question 24

What are the three ways to ensure fidelity of DNA information

Answer 24

1.Redundancy- either strand of the double helix can specify the sequence of the other strand
2.Precision of cellualr replication machinery- DNA polymerase I and III have proofreading ability
3.DNA repair enzymes