Question

What is the correct sequence of polymerase Chain Reactions? A. Annealing, B. Extension, C. Final extension, D. Heat-denaturation, E. Storage ($4^{\circ}\text{C}$) Choose the correct answer from the options given below:

• A. E, A, C, B, D \
• B. A, D, B, C, E \
• C. D, A, B, C, E \
• D. E, B, A, C, D

Hint:

Remember the core PCR triplet acronym: Denature $\rightarrow$ Anneal $\rightarrow$ Extend (D $\rightarrow$ A $\rightarrow$ B), followed by the final cleanup and cold storage steps.

Answer 1

The Correct Option is C

Step 1: Concept A standard PCR cycle consists of distinct, temperature-dependent stages that are repeated multiple times to exponentially amplify a target DNA sequence.

Step 2: Meaning The reactions must proceed in a strict structural order to allow the template strands to separate, the primers to bind, and the polymerase to extend the new strands.

Step 3: Analysis Let us follow the steps of a typical PCR program run: 1. Heat-denaturation (D): The sample is heated to around $94^{\circ}\text{C}$ to break hydrogen bonds and separate the double-stranded DNA into single strands. 2. Annealing (A): The temperature is lowered to around $55^{\circ}\text{C}$ to allow forward and reverse primers to bind to their complementary targets on the single-stranded DNA. 3. Extension (B): The temperature is raised to $72^{\circ}\text{C}$, the optimal working temperature for Taq polymerase, to synthesize the new complementary DNA strands. 4. Final extension (C): After the final cycle, the reaction is held at $72^{\circ}\text{C}$ for a few minutes to ensure all remaining single-stranded strands are fully extended. 5. Storage (E): The machine cools down and holds the completed reaction at a safe storage temperature of $4^{\circ}\text{C}$.

Step 4: Conclusion The correct ordered sequence of stages is D $\rightarrow$ A $\rightarrow$ B $\rightarrow$ C $\rightarrow$ E, which matches option C. Final Answer: (C)