Question
Identify the correct sequence of steps in each cycle of Polymerase Chain Reaction :
This question was previously asked in
NEET UG Re-Exam 2026 Question Paper (21-Jun-2026)
The correct answer is
Denaturation $\rightarrow$ Annealing $\rightarrow$ Extension
Polymerase Chain Reaction (PCR) Cycle Steps
Polymerase Chain Reaction (PCR) is a technique used to amplify specific DNA sequences. It involves repeated cycles, each consisting of three key temperature-dependent steps:
PCR Cycle Sequence
- Denaturation: The reaction mixture is heated to a high temperature, typically around $94-98^\circ C$. This heat breaks the hydrogen bonds holding the two strands of the DNA template together, separating them into single strands.
- Annealing: The temperature is then lowered, usually to $50-65^\circ C$. This allows short DNA sequences called primers to bind (anneal) to complementary bases on the single-stranded DNA templates.
- Extension: The temperature is raised to an optimal point for the DNA polymerase enzyme, typically around $72^\circ C$. The polymerase enzyme attaches to the primers and synthesizes a new complementary DNA strand, extending from the primer along the template strand.
These three steps—Denaturation, Annealing, and Extension—constitute one cycle of PCR. This cycle is repeated multiple times (usually 25-35 cycles) to exponentially amplify the target DNA sequence.
Therefore, the correct sequence of steps in each cycle of Polymerase Chain Reaction is Denaturation $\rightarrow$ Annealing $\rightarrow$ Extension.
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