Question

Which of the following is favoured for designing primers that are required during PCR?

• A. There should be two sets of primers - forward and reverse
• B. Primer should be atleast 50 nucleotides long
• C. The forward and reverse primers should not be complementary to each other
• D. Both a and c

Answer 1

The correct option is D Both a and c

PCR or polymerase chain reaction is a technique used in molecular biology to create several copies of a certain DNA segment. This involves using two sets of primers (forward primer and reverse primer which attach to the 3' OH ends of the DNA strands oriented in 3’→5’ and 5’→3’ polarity, respectively) and thermostable DNA polymerase.

In PCR, a short segment of DNA is amplified using primers and enzymes. Taq polymerase extends a new strand of DNA complementary to the template DNA at the desired sequence. The Taq polymerase can add a nucleotide to the pre-existing 3’-OH group only. Therefore, a primer is required.

Primers for the PCR are designed in such a way that the length should be around 15-30 nucleotides. The forward and reverse primers should not be complementary to each other, otherwise they will bind to complementary sequences and form a double-stranded structure. The template DNA will be left as it was unamplified.