Unit 1 Key area 2

Question 1

State what is meant by a “primer”?

Answer 1

A primer is a short strand of nucleotides that joins to the 3’ end of the DNA template strand and allows the DNA polymerase to begin to add free nucleotides in a 5’ to 3’ direction.

Question 2

What is the role of DNA polymerase in the replication of DNA?

Answer 2

DNA is replicated by DNA polymerase, which adds free nucleotides across the template strand in a 5’ to 3’ direction.

Question 3

Give an account of DNA replication?

Answer 3

During DNA replication, the weak hydrogen bonds between DNA molecules will be broken down and two template strands will form because of this. A short strand of nucleotides called a primer will add across the 3’ end of the template strand. This primer allows the enzyme DNA polymerase to add free nucleotides in a 5’ to 3’ direction

The anti-parallel structure of the DNA molecule means that a leading and lagging strand will be produced.

Question 4

State what is meant by a “leading strand”?

Answer 4

A leading strand is the strand in which free DNA nucleotides are added continuously in a 5’ to 3’ direction as a result of the DNA replication fork opening in that direction.

Question 5

State what is meant by a “lagging strand”?

Answer 5

The lagging strand is the strand in which DNA must be added in fragments. as the DNA replication fork runs in a 3’ to 5’ direction meaning that primers must be added continuously to allow the new strand to from.

Question 6

State the role of the enzyme ligase in DNA replication?

Answer 6

Ligase joins together the Fragments in the lagging strand.

Question 7

Explain what a PCR is used for?

Answer 7

A PCR is used to “amplify” a sample of DNA using “complementary primers” for the “specific target sequence”

Question 8

What can be said about the primers used in a PCR?

Answer 8

In PCR primers are short strands of nucleotides complementary to the specific target sequence of the DNA being amplified.

Question 9

Give two examples of apparatus that can be used to carry out a PCR?

Answer 9

• Thermocyclers
• Water baths

Question 10

Give an account of the process of PCR?

Answer 10

• The solution is heated to between 92°C and 98°C, here the hydrogen bonds between the samples of DNA will break down.
• The solution is then cooled down to between 50°C and 65°C to allow complementary primers to bind to their specific target sequences.
• The solution is then heated again to between 70°C and 80°C to allow heat tolerant DNA polymerase to being to add free nucleotides across the template strand.

Question 11

Give 3 examples of the uses of PCR?

Answer 11

• PCR can be used to settle paternity suits
• PCR can be used in forensic science to solve crimes
• PCR can be used to identify genetic disorders