Question

In the three steps (a, b, c) of polymerase chain reaction, select the correct step.

• A. a - Annealing with two sets of primers
• B. b - Denaturation at high temperature
  
• C. a - Denaturation at 50°C
• D. c - Extension in presence of heat stable DNA polymerase
  

Answer 1

The correct option is D c - Extension in presence of heat stable DNA polymerase


Polymerase Chain Reaction
Polymerase chain reaction (PCR) is a technique used for the in vitro amplification of the DNA fragments or gene of interest to create multiple copies.

Steps involved in PCR
Steps involved in PCR is as follows:
a. Denaturation - In this step separation of the two strands of double stranded DNA done by application of heat at 94 - 95°C.
b. Annealing - This step involves the hybridisation of the primers with specific sequences of each of the strands of the template DNA. Primers are small oligonucleotides up to 18 - 24 nucleotides long synthesised chemically. This process is carried out at 50 - 56°C.
c. Extension or synthesis - In this step the Taq DNA polymerase synthesises DNA by adding dNTPs (deoxyribonucleotides) to the free ends of the primers. The extension of DNA is carried out at 72°C. This helps in synthesising complementary strands.

Labelled image of PCR
Labelled image of PCR:

Final answer
(A) c - Extension in presence of heat stable DNA polymerase