Select the components that are needed to set up a polymerase chain reaction:
(A) Two primers and dNTPs
(B) Template DNA
(C) DNA ligase
(D) DNA polymerase
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (A), (B) and (D) only
Polymerase chain reaction (PCR) makes many copies of a chosen piece of DNA in a test tube, by repeating the copying of DNA again and again.
(A) Two primers and dNTPs — Needed. The primers are short pieces of DNA that mark the two ends of the region to be copied. The dNTPs are the nucleotides from which the new strands are built.
(B) Template DNA — Needed. The DNA to be copied serves as the template for every new strand.
(C) DNA ligase — Not needed. Ligase joins two DNA pieces. In PCR each new strand is made in one piece from its primer, so nothing has to be joined.
(D) DNA polymerase — Needed. It extends the primers using the nucleotides. A thermostable enzyme from Thermus aquaticus is used, because it survives the high temperature of each cycle.
NCERT Extract:
Amplification of Gene of Interest Using PCR – “… PCR stands for Polymerase Chain Reaction. In this reaction, multiple copies of the gene (or DNA) of interest is synthesised in vitro using two sets of primers (small chemically synthesised oligonucleotides that are complementary to the regions of DNA) and the enzyme DNA polymerase. The enzyme extends the primers using the nucleotides provided in the reaction and the genomic DNA as template. If the process of replication of DNA is repeated many times, the segment of DNA can be amplified to approximately billion times, i.e., 1 billion copies are made.”