Unit 1.2 Replication of DNA

Question 1

What is a primer?

Answer 1

A short strand of nucleotides which binds to the 3’ end of a DNA template strand (creating the 5’ end)

Question 2

What is the role of a primer in DNA replication?

Answer 2

To Bind to the 3’ end of a template strand and allow DNA polymerase to begin to add free nucleotides across the template strand

Question 3

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

Answer 3

Adds DNA nucleotides using complementary base pairing in the direction of the 3’ deoxyribose end

Question 4

What are the key events of DNA replication?

Answer 4

DNA is unwound and uncoiled and the hydrogen bonds between the complementary bases are broken down, this creates two template strands, primers are added to the 3’ end and they enable DNA polymerase to begin adding nucleotides in the 5’ to 3’ direction

Question 5

What is meant by a lagging strand of DNA?

Answer 5

A strand of DNA in which primers must be continuosly added to the 3’ end of the strand in order for DNA polymerase to add DNA nucleotides in the 5’ to 3’ direction.

Question 6

What enzyme is required for the lagging strand and what is the role it plays?

Answer 6

Ligase, which joins fragments of DNA nucleotides together.

Question 7

What is meant by a leading strand of DNA?

Answer 7

The strand in which a primer is added at the 3’ end and DNA polymerase can continuously add nucleotides in a 5’ to 3’ direction as the DNA replication fork expands

Question 8

What does PCR do?

Answer 8

Amplifies a DNA sample using complementary primers for specific target sequences

Question 9

What is special about the primers that are used in PCR?

Answer 9

In PCR primers are complementary to the specific target sequences at the two ends of the region of DNA being amplified.

Question 10

PCR uses repeated cycles of heating and cooling to amplify a sample of DNA what are the stages in this process?

Answer 10

Firstly the sample is heated at between 92 - 98 C , this is done to separate the strands of DNA by breaking down the hydrogen bonds. It is then cooled down at between 50 - 65 C to allow complementary primers to bind to their specific target sequences. It is then heated again to between 70 - 80 C, to allow the heat tollerant strain of DNA polymerase replicate the region of the DNA

Question 11

What are some of the practical uses of PCR?

Answer 11

• Settle paternity suits
• diagnose genetic disorders
• help solve crimes in forensics