Question

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 ?

• A. A - Denaturation at a temperature of about 50^o C.
• B. B-Denaturation at a temperature of about 98^o C separating the two DNA strands.
• C. C - Extension in the presence of heat stable DNA polymerase.
• D. A- Annealing with two sets of primers.

Answer 1

Answer: (C)

PCR is a technique for enzymatically replicating DNA without using a living organism such as E. coli or yeast. It is commonly used in medical and biological research labs for a variety of tasks like detection of hereditary diseases identification of genetic fingerprints etc.
The correct steps shown in the above figure are:
A - Denaturation at a temperature of about 94^o to 98^oC. During the denaturation, the double strand melts open to single stranded DNA, and all enzymatic reactions stop.
B - Annealing (binding of DNA primer to the separated strands. Occurs at 50^o to 65^oCelsius, which is lower than the optimal temperature of the DNA polymerases)
C - Extension or elongation of the stands using the DNA primer with heat-sable DNA polymerases, most frequently Taq (Thermus aquaticus) at 72^oC.