Arrange the following steps of PCR in the correct sequence.
(A) Annealing of primers
(B) Denaturation of DNA
(C) Extension by DNA polymerase
(D) Amplification of desired DNA
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → (B), (A), (C), (D)
(B) Denaturation of DNA — this comes first. High temperature separates the two strands of the DNA, so each strand can act as a template.
(A) Annealing of primers — this comes second. The primers are short, chemically made pieces of DNA. Each one binds to the part of the single strand that is complementary to it.
(C) Extension by DNA polymerase — this comes third. The enzyme DNA polymerase adds nucleotides to the primers and builds the new strands. It is a heat-stable enzyme from the bacterium Thermus aquaticus, so it keeps working at the high temperature of the next cycle.
(D) Amplification of desired DNA — this comes last. When the three steps are repeated many times, the DNA segment is copied to about a billion copies.
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