Unit 1 - KA 2: Replication Of DNA

Question 1

Names the enzyme required for DNA replication.

Answer 1

DNA polymerase.

Question 2

Define the term primer.

Answer 2

A primer is a short strand of DNA nucleotides that binds 3’ end of a DNA strand.

Question 3

Explain why primers are necessary for DNA replication.

Answer 3

DNA polymerase can only add nucleotides to an existing chain so a primer is placed at the 3’ end to allow DNA polymerase to add nucleotides to a new strand.

Question 4

Describe the order of events in DNA replication.

Answer 4

• DNA unwinds and hydrogen bonds break to form two template strands.
• Primers bind to complementary bases at the 3’ end of the template strands
• DNA nucleotides flood in and join with complementary bases via hydrogen bonds
• DNA polymerase joins nucleotides to the 3’ end of the new DNA strand creating a sugar phosphate bond.
• DNA fragments found on the lagging strand are sealed together using ligase.
• each daughter strand rewinds.

Question 5

Explain why the lagging strand is synthesised in fragments.

Answer 5

The lagging strand must be synthesised in fragments because DNA polymerase can only add nucleotides to the 3’ end of a growing strand.

Question 6

Name the enzyme that joins the fragments together on the lagging strand.

Answer 6

Ligase

Question 7

What is PCR

Answer 7

Polymerase Chain Reaction is a technique used for the amplification of DNA.

Question 8

List the three temperatures that are cycled through.

Answer 8

92-98°C
50-65°C
70-80°C

Question 9

List the three temperatures that are cycled through.

Answer 9

92-98°C
50-65°C
70-80°C

Question 10

What happens at the first temperature in the cycle of PCR.

Answer 10

The hydrogen bonds break, allowing the strands to separate.

Question 11

What happens at the second temperature in the cycle of PCR.

Answer 11

Primers attach/bind to their target sequence.

Question 12

What happens at the third temperature in the cycle of PCR.

Answer 12

Heat tolerant DNA polymerase replicates the region of DNA.

Question 13

Name the enzyme used in PCR.

Answer 13

Heat tolerant DNA polymerase.

Question 14

Explain why the enzyme used in PCR must be heat tolerant.

Answer 14

To prevent the enzyme from becoming denatured due to high temperatures.

Question 15

State three practical applications of PCR.

Answer 15

Help solve crimes, settle paternity suits and diagnose genetic disorders.

Question 16

Describe what gel electrophoresis is used for.

Answer 16

Gel electrophoresis is a technique used to separate strands of DNA and protein molecules.