Question

During PCR cycle, the temperature range in the step of annealing is________

• A. $40 - 60^\circ\text{C}$
• B. $90 - 98^\circ\text{C}$
• C. $70 - 75^\circ\text{C}$
• D. $65 - 85^\circ\text{C}$

Hint:

PCR mnemonic: D-A-E = Denature (95$^\circ$C), Anneal (50$^\circ$C), Extend (72$^\circ$C).

Answer 1

The Correct Option is A

Concept:
Polymerase Chain Reaction (PCR) consists of three main steps, each occurring at specific temperature ranges:
• Denaturation
• Annealing
• Extension

Step 1: Recall PCR temperature ranges.
• Denaturation → $90 - 98^\circ$C (DNA strands separate)
• Annealing → $40 - 60^\circ$C (primers bind to template DNA)
• Extension → $70 - 75^\circ$C (Taq polymerase synthesizes DNA)

Step 2: Understand annealing step. During annealing, primers attach (hybridize) to complementary sequences on the DNA template. This requires a lower temperature to allow hydrogen bond formation.

Step 3: Analyze options.
• (A) $40 - 60^\circ$C → Correct annealing range \checkmark
• (B) $90 - 98^\circ$C → Denaturation $\times$
• (C) $70 - 75^\circ$C → Extension $\times$
• (D) $65 - 85^\circ$C → Not standard for annealing $\times$

Step 4: Conclusion. Thus, the annealing temperature range is: \[ 40 - 60^\circ\text{C} \]