Replication of DNA

Question 1

What enzyme is responsible for DNA replication?

Answer 1

DNA polymerase

Question 2

What is the function of a primer?

Answer 2

To provide a start point for DNA polymerase.

Question 3

Why is DNA replication required?

Answer 3

Before mitosis to ensure that both daughter cells get an identical copy of the genetic information from the parent cell.

Question 4

What is required in order for DNA replication to take place?

Answer 4

Enzymes, DNA nucleotides, primers, template DNA, ATP

Question 5

Which enzyme joins the fragments of DNA on the lagging strand?

Answer 5

Ligase

Question 6

Which bonds are broken to separate the two strands of DNA?

Answer 6

Hydrogen bonds

Question 7

Why can DNA only be replicated in one direction?

Answer 7

Because DNA polymerase can only add nucleotides to the 3’ end.

Question 8

What is meant by discontinuous synthesis?

Answer 8

Strand is replicated in fragments

Question 9

What is meant by continuous synthesis?

Answer 9

Whole strand is made in one piece.

Question 10

What is the function of PCR?

Answer 10

To amplify a sequence of DNA.

Question 11

What are the requirements of PCR?

Answer 11

Template DNA, taq polymerase, primers, free DNA nucleotides, buffer

Question 12

When is PCR used?

Answer 12

Crime scene analysis to identify suspects, paternity testing, identifying evolutionary relationships.

Question 13

Why are there multiple replication forks on one strand of DNA?

Answer 13

To allow speedy replication.

Question 14

Why is DNA heated in the first stage of PCR?

Answer 14

To break the hydrogen bonds between the bases and separate the two strands.

Question 15

Why is DNA cooled during the second stage of PCR?

Answer 15

To allow primers to anneal to the template strands.

Question 16

Why is taq polymerase used in PCR?

Answer 16

It doesn’t denature during the heating cycles.

Question 17

Why is DNA heated back up for the third stage of PCR?

Answer 17

To allow taq polymerase to synthesise the new strands of DNA.

Question 18

Why are two different primers needed during PCR?

Answer 18

One which is complementary to each strand being copied.

Question 19

What temperature does the first stage of PCR occur at?

Answer 19

94-96°C (any within range)

Question 20

What temperature does the second stage of PCR occur at?

Answer 20

55°C and 65°C (any within range)

Question 21

What temperature does the third stage of PCR occur at?

Answer 21

72°C

Question 22

Why is there a leading and lagging strand in DNA replication?

Answer 22

Parent strands are anti-parallel but DNA can only be synthesised in 5’ - 3’ direction.

Question 23

What is the difference between DNA polymerase and taq polymerase?

Answer 23

DNA polymerase denatures at lower temperatures than taq polymerase.

Question 24

What is meant by a negative control in PCR?

Answer 24

Doing it without DNA sample to ensure no contamination.

Question 25

What is meant by a positive control in PCR?

Answer 25

Doing it with a sample of DNA you know will copy to ensure everything is working.

Question 26

Which bonds are synthesised by DNA / taq polymerase?

Answer 26

Strong chemical bonds / covalent bonds between sugar and phosphates of adjacent nucleotides.

Question 27

Which rule allows the molecules of DNA to be copied?

Answer 27

Complementary base pairing rule

Question 28

Which strand in DNA replication requires the use of many primers?

Answer 28

Lagging strand