Question

In a polymerase chain reaction after the denaturation step why the mixture needs to cool down to a lower temperature?
A. To permit specific annealing of the primers.
B. To give a halt to the reaction mixture.
C. To increase the activity of enzyme Taq polymerase
D. To obtain multiple copies of DNA.

Answer 1

Hint: PCR is the polymerase chain reaction method which is used to make millions of copies of DNA samples rapidly, it was developed by Kary Mullis in the 1980S, basically it is a DNA amplification process. This process is used to detect various kinds of disease, to detect convicts and for pedigree analysis.

Complete answer:
In PCR in DNA sequence mainly four-step are involved and the name as:-
> Denaturation: This phase requires the high temperature almost 90 degree Celsius, to separate the double-stranded DNA into two single-stranded, the hydrogen bond breaks at high temperature, this process is known as denaturation.

> Annealing primer to target sequence: This phase requires low temperature as compared to denaturation phase, in this phase primer is bound to a specific site of DNA segment and marks the sequence for the replication or copying process. In annealing, primer binds with the complementary single DNA strand.

> Extension: In this phase temperature rises nearly 72 degree Celsius after binding of primer to DNA, Taq DNA polymerase is required to replicate DNA strands, and it forms the sequence in the 5’ to 3’ direction. This enzyme is good for working at high temperatures.

> End of the first PCR cycle: In this phase, two new DNA strands are present which are identical to the original.

Hence, the correct answer is option (A).

Note: PCR (Polymerase Chain Reaction) is used in any way and has a wide range of applications such as genotyping, cloning, mutation detection, forensics, sequencing, microarrays, paternity testing. Nested PCR is used to reduce the nonspecific binding by utilizing two sequential runs of PCR.