Question

Which of the following is not a step of Polymerase Chain Reaction?

• A. Extension
• B. Downstream processing
• C. Annealing
• D. Denaturation

Answer 1

The Correct Option is B

The Polymerase Chain Reaction (PCR) is a widely used technique in molecular biology for amplifying DNA. It consists of three main steps:

• Denaturation: This step involves heating the double-stranded DNA to around 94-98°C to break the hydrogen bonds between the strands, resulting in two single-stranded DNA molecules.
• Annealing: The temperature is lowered to 50-65°C to enable the primers to bind (anneal) to their complementary sequences on the single-stranded DNA. 
• Extension: During this step, the temperature is set to around 72°C. Taq polymerase, the enzyme used in PCR, synthesizes a new DNA strand by extending the primers using the original single strand as a template.

The correct identification of these steps is crucial for understanding the process of PCR. In the options given, Downstream processing is the correct answer as it is not a step in Polymerase Chain Reaction but rather a part of bioprocessing that involves the purification and recovery of products derived from biotechnological processes. Thus, it falls outside the scope of PCR steps.

Answer 2

The Polymerase Chain Reaction (PCR) involves the following key steps:

• Denaturation: The DNA template is heated to separate its two strands.
• Annealing: Short DNA primers bind to the complementary sequences on the single-stranded DNA.
• Extension: DNA polymerase extends the primers to synthesize new DNA strands.

Downstream processing, on the other hand, is not a step of PCR. It refers to the processes used to purify and isolate the desired product after PCR or other biotechnological techniques, like protein purification or product extraction.