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

Topic: Molecular Biology (PCR)
Polymerase Chain Reaction (PCR) is a technique used to make millions of copies of a specific DNA segment through repeated cycles of heating and cooling.
Steps:
Understanding the Question: The question asks for the chronological order of the three main thermal phases that occur in one single PCR cycle.
Key Formulas and Approach: PCR follows a logical physical process: first, separate the strands; second, let primers find their match; third, build the new strands.
Detailed Solution:
Denaturation: High heat ($\sim 94^\circ C$) is applied to break the hydrogen bonds between DNA strands, turning double-stranded DNA into single strands.
Annealing: The temperature is lowered ($\sim 50-65^\circ C$) so that DNA primers can bind (anneal) to their complementary sequences on the template strands.
Extension: The temperature is raised slightly ($\sim 72^\circ C$) so that Taq polymerase can add dNTPs to the primers, synthesizing a new DNA strand.