The correct order of steps in Polymerase Chain Reaction (PCR) is
Answer: (D) Denaturation, Annealing, Extension. Answer: (4) Denaturation, Annealing, Extension Solution: Each PCR cycle proceeds in a fixed order: denaturation (strand separation by heat), then primer annealing (primers bind complementary regions), then extension of primers by DNA polymerase.
- A.Denaturation, Extension, Annealing
- B.Annealing, Extension, Denaturation
- C.Extension, Denaturation, Annealing
- D.Denaturation, Annealing, Extension✓
Correct Answer
(D) Denaturation, Annealing, Extension
Solution & Explanation
Answer: (4) Denaturation, Annealing, Extension Solution: Each PCR cycle proceeds in a fixed order: denaturation (strand separation by heat), then primer annealing (primers bind complementary regions), then extension of primers by DNA polymerase. The other sequences invert this logical dependency — annealing cannot precede strand separation, and extension cannot precede primer binding. NCERT lists the three steps in exactly this order in the PCR figure caption. NCERT Reference: Ch 9, p.172, line(s) 19-20 — "Each cycle has three steps: (i) Denaturation; (ii) Primer annealing; and (iii) Extension of primers"