Question

Mention the three steps involved in each cycle of Polymerase-chain Reaction (PCR). How is repeated amplification of DNA made possible during PCR

Answer 1

In a PCR reaction, DNA polymerase synthesises a new DNA strand complementary to the DNA template by adding nucleotide to the primers. The above components are mixed together in PCR tubes and run on a thermal cycler, where they go through multiple cycles involving the following reactions:

Denaturation – This step involves heating the reaction mixture to a high temperature (94°C). This denatures the double-stranded DNA template into single-strands by breaking the weak hydrogen bonds between the two DNA strands.

• Annealing – In this step, the reaction mixture is brought to a temperature of 54-60°C, to allow the primers to bind (anneal) to their complementary sequence in the template DNA.
  
• Elongation/Extension – In this step, the DNA polymerase sequentially adds nucleotides to the primers and extends it in the 5′ to 3′ direction.
  

One cycle of denaturation, annealing, and elongation amplifies the double-stranded DNA template to give two pieces of double-stranded DNA. The cycles keep repeating to produce more and more copies, increasing the number of copies exponentially.