Question

What is the standard sequence of steps in a PCR (Polymerase Chain Reaction) cycle?

• A. Annealing → Denaturation → Extension
• B. Denaturation → Annealing → Extension
• C. Extension → Denaturation → Annealing
• D. Annealing → Extension → Denaturation

Hint:

Remember PCR steps using the mnemonic {DAE}:
{D}enaturation → {A}nnealing → {E}xtension.

Answer 1

The Correct Option is B

Concept: Polymerase Chain Reaction (PCR) is a molecular biology technique used to amplify a specific segment of DNA. It involves repeated cycles of temperature changes that allow DNA strands to separate, primers to bind, and new DNA strands to be synthesized. Each PCR cycle consists of three main steps.
Step 1:Denaturation.
The reaction mixture is heated to about (94^\circ C - 98^\circ C). At this high temperature, the double-stranded DNA separates into two single strands as the hydrogen bonds between complementary bases break.
Step 2:Annealing.
The temperature is lowered to approximately (50^\circ C - 65^\circ C). At this stage, short DNA primers bind (anneal) to their complementary sequences on the single-stranded DNA templates.
Step 3:Extension (Elongation).
The temperature is raised to around (72^\circ C), which is the optimal temperature for the enzyme {Taq polymerase}. The enzyme adds nucleotides to the primer and synthesizes a new DNA strand complementary to the template. Thus, the correct order of PCR steps is: [ \text{Denaturation} \rightarrow \text{Annealing} \rightarrow \text{Extension} ]