HIGHER Replication of DNA

Question 1

What must happen prior to cell division?

Answer 1

DNA must be replicated exactly, by DNA polymerase

Question 2

Describe the process of DNA replication in living cells

Answer 2

• DNA is unwound and hydrogen bonds between bases are broken to form to template strands
• The enzyme DNA polymerase needs primers to start replication. A primer is a short strand of nucleotides which binds to the 3’ end of the template DNA strand
• The primer allows DNA polymerase to addd DNA nucleotides, using complementary base pairing, to the 3’ (deoxyribose) end of the primer/new DNA strand which is forming
• DNA polymerase can only add nucleotides in one direction (3’ to 5’), resulting in the leading strand being replicated continuosly and the lagging strand replicated in fragments
• The fragments of DNA (on the lagging strand) are joined together by (the enzyme) ligase

Question 3

What is The Polymerase Chain Reaction (PCR)?

Answer 3

PCR is an automated process that amplifies DNA using complementary primers for specific target sequences. Practical appliactions of PCR are that it can amplify DNA to help solve crimes, settle paternity suits, and diagnose genetic disorders.

Question 4

Describe the process of PCR

Answer 4

In PCR, primers are short strands of nucleotides which are complementary to specific target sequences at the two ends of the region of the DNA to be amplified. During PCR there are repeated cycles of heating and cooling to amplify DNA:

• stage 1: DNA is heated to between 92 and 98C to separate the DNA strands.
• stage 2: DNA is then cooled to between 50 and 65C to allow primers to bind target sequences.
• stage 3: It is then heated to between 70 and 80C for heat-tolerant DNA polymerase to replicate the region of DNA