Which of the following represents the correct sequence of steps in the polymerase chain reaction (PCR)?

Appeared in: PGICH Noida NO-2025

Explanation

The correct sequence for PCR is a three-step cycle: Denaturation, Annealing, and Extension.
First, Denaturation at a high temperature (around 95°C) is required to separate the double-stranded DNA into single strands.
Next, Annealing occurs at a lower temperature (around 55°C), allowing primers to bind to the single-stranded DNA templates.
Finally, Extension happens at an intermediate temperature (around 72°C), where DNA polymerase synthesizes new DNA strands, completing the cycle.

Option B: Hybridization is not a separate step after extension. The annealing step itself is a form of hybridization, where the primers bind to the DNA template.
Option C: This sequence is incorrect. Annealing (binding primers) cannot occur before the DNA double helix is separated by denaturation.
Option D: This sequence is incorrect. Extension (synthesis) cannot happen without primers first being annealed to the DNA template, and annealing cannot happen before denaturation.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Steps of Polymerase Chain Reaction (PCR) as background academic context rather than a clinical decision trigger.
PCR is a fundamental diagnostic tool in modern healthcare. Nurses often handle specimens for PCR testing and need to understand its significance for patient diagnosis.
It allows for the rapid detection of infectious agents like SARS-CoV-2 (COVID-19), HIV, and influenza, enabling timely treatment and infection control measures.
PCR is used to monitor viral load in patients with chronic infections like HIV or Hepatitis C, helping to assess the effectiveness of antiviral therapy.

How to Approach the Question

First, identify the core concept of the question, which is the procedural order of the Polymerase Chain Reaction (PCR).
Recall the purpose of PCR: to amplify DNA. This requires copying DNA strands.
Think logically about the process of copying DNA. You must first separate the original template (Denaturation).
Next, you need a starting point for the copying process, which involves attaching primers (Annealing).
Finally, the new DNA strand is built from that starting point (Extension/Synthesis).
This logical flow—separate, attach, build—corresponds to Denaturation → Annealing → Extension. Compare this sequence to the given options to find the correct answer.

Concept Tested & Keywords

QTDboxGGnS_0zjfs4dFPfE

E6 Biochemistry U Satyanarayana— Part 2 (pp 421-820 of 840) pp. 222-224, 223-225

E6 Harper's Illustrated Biochemistry2023 (pp 26-793 of 813) p. 436-438

Practise the full PGICH Noida NO-2025

Attempt every question from this paper in a timed mock, then review the full solution for each one.