Question

The polymerase chain reaction is a technique that
a) is used for in vivo replication of DNA
b) is used for in vivo synthesis of mRNA
c) is used for in vitro synthesis of mRNA
d) used for in vitro replication of specific DNA sequence

Answer 1

Hint: PCR is an abbreviated form of Polymerase Chain reaction, which was formulated by Kary Mullis in 1985. PCR consists of a series of cycles of three successive reactions namely Denaturation, Annealing, and Extension. These three steps constitute 1 cycle of PCR amplification. This process can be carried out repetitively just by changing the temperature of the reaction mixture.

Complete answer:
PCR is a swift and versatile in-vitro method for amplifying a defined target DNA sequence present within the sample of DNA. The essential components needed for PCR include thermostable DNA polymerase, primers, dNTP, divalent cations, buffer, and template DNA.
Usually, the PCR method is designed to permit selective amplification of DNA sequence within a heterogeneous collection of DNA molecules. To permit such selective amplification, some former DNA sequence information from the target sequence is necessary. This information is used to design two oligonucleotides primers which are specific to the target DNA sequence and are often 15-20 nucleotides long. When the primers are added to denatured template DNA, they bind precisely to complementary DNA sequences at the target site. In the presence of appropriate heat-stable DNA polymerase and DNA precursors, primers initiate the synthesis of new DNA strands which are complementary to the individual DNA strand of the target DNA segment.

Hence, the correct answer is (d).

Note:
The PCR is a chain reaction because newly synthesized DNA strands will act as templates for further DNA synthesis in subsequent cycles. Primer designing is the most important aspect for selective amplification as this prevents the primers from binding to sites other than the desired one.