Biotechnology- Principles and Processes Question 58
58. The figure below shows three steps (A, B, C) of Polymerase Chain Reaction (PCR). Select the option giving correct identification together with what it represents?
[2012M]
(a) B - Denaturation at a temperature of about $98^{\circ} C$ separating the two DNA strands.
(b) A - Denaturation at a temperature of about $50^{\circ} C$.
(c) $C$ - Extension in the presence of heat stable DNA polymerase.
(d) A - Annealing with two sets of primers.
Show Answer
Answer : c
Hints & Solutions
(c) PCR is a technique for enzymatically replicating DNA without using a living organism such as E. coli or yeast. The correct steps shown in the above figure are:
A - Denaturation at a temperature of about $94^{\circ}$ to $98^{\circ} C$. During the denaturation, the double stranded DNA open to single stranded DNA, and all enzymatic reactions stop.
B - Annealing (binding of DNA primer to the separated strands. Occurs at $50^{\circ}$ to $65^{\circ} C$, which is lower than the optimal temperature of the DNA polymerases)
C - Extension or elongation of the strands using the DNA primer with heat-stable DNA polymerases, most frequently Taq (Thermus aquaticus) at $72^{\circ} C$.
PCR is commonly used in medical and biological research labs for a variety of tasks like detection of hereditary diseases, identification of genetic fingerprints etc.
