Question

Match the following steps of PCR to their respective temperatures.
$\begin{array}{cc}\text{PCR steps}& \text{Temperature}\\ \text{P. Denaturation}& \text{i.}{72}^{\circ }C\\ \text{Q. Annealing}& \text{ii.}92-{96}^{\circ }C\\ \text{R. Extension}& \text{iii.}55-{65}^{\circ }C\end{array}$

• A. P - i, Q - ii, R - iii
• B. P - ii, Q - i, R - iii
• C. P - iii, Q - ii, R - i
• D. P - ii, Q - iii, R - i

Answer 1

The correct option is D P - ii, Q - iii, R - i

PCR or polymerase chain reaction is a technique used in molecular biology to create several copies of a certain DNA segment.

PCR occurs in three steps:

- Denaturation: The temperature is maintained at 92-96℃. The high temperature melts the hydrogen bonds between the two strands of a double-stranded DNA molecule. This helps in unwinding and strand separation.

- Annealing: It occurs at 55-65℃. The two oligonucleotide primers anneal with the separate DNA strands at their complementary sequences.

- Extension: It is carried out at 72℃. It involves the addition of deoxyribonucleotides to the free 3' OH ends of primers and helps in subsequent elongation of the complementary new strands. This is catalysed by Taq polymerase.