Question

Which one of the following is not a component required for Polymerase Chain Reaction (PCR) ?

• A. Template DNA
• B. Primers
• C. DNA Ligase
• D. DNA Polymerase

Hint:

PCR needs template, primers, Taq polymerase and nucleotides. Ligase joins fragments in cloning, not in PCR.

Answer 1

The Correct Option is C

Step 1: Understand the question:
PCR (Polymerase Chain Reaction) is a laboratory method that makes millions of copies of a chosen stretch of DNA.
The reaction runs in a thermal cycler, and each cycle doubles the amount of target DNA.
We must pick the item that is not added to the PCR tube.

Step 2: List what a PCR tube contains:
The tube holds the template DNA, two primers, a thermostable DNA polymerase, the four deoxynucleotides (dATP, dGTP, dCTP, dTTP) and a buffer with \( \mathrm{Mg^{2+}} \).
Each cycle has three stages: denaturation at about 94 degrees C, annealing at about 50-60 degrees C and extension at about 72 degrees C.

Step 3: Check options (A), (B) and (D):
(A) Template DNA is the DNA that carries the target region to be copied, so it is needed.
(B) Primers are short single-stranded DNA pieces that bind to the template and give the polymerase a starting point, so they are needed.
(D) DNA polymerase (Taq polymerase) adds nucleotides to the primers and builds the new strands, so it is needed.

Step 4: Check option (C):
DNA ligase joins two DNA pieces by sealing the gap between them with a phosphodiester bond.
It is used in recombinant DNA work to join the vector and the insert.
PCR only extends primers into new strands, so no joining of separate fragments is needed.
So DNA ligase is not a PCR component.

Final Answer:
DNA ligase is not required for PCR, so the correct option is (C). \[ \boxed{\text{(C) DNA Ligase}} \]