Question

What does PCR stand for? What is its principle? Name the three different steps involved in this reaction.

Answer 1

Hint: DNA amplification can be done artificially using PCR. It uses a polymerase enzyme obtained from a thermophilic bacterium Thermus aquaticus.

Complete answer:
PCR stands for Polymerase chain reaction (PCR). It is a widely used technique of DNA amplification. The technique was given by Kary Mullis.

Principle: This technique amplifies gene in-vitro to produce billions of copies of particular DNA in a short time.

It consists of 3 steps:
- Denaturation: The separation of two strands is called denaturation. Dilute acid or base or heating at high temperature can be used for denaturation. Usually DNA is heated at $90-94^o$C for a short time. $92^o$C is the optimum temperature for this step.

- Annealing: It means hybridization. A new DNA is synthesized on separated strands. To synthesize new DNA, a primer is required. Primer is a small fragment of RNA. It requires $50-60^o$C. $56^o$C is optimum temperature.

- Extension: A new DNA is synthesized in this step. This step requires $72^o$C. An enzyme called DNA polymerase is required for this step. But it is isolated from a thermophilic bacterium Thermus aquaticus, hence it is called Taq polymerase. DNA nucleotides are added.

These three steps make one cycle of PCR.
PCR is widely used in medical, forensic and biological labs for a variety of applications.

Note: DNA polymerase in humans works at $37^o$C, hence in PCR a different type of DNA polymerase is required which can work at high temperature. As human DNA polymerase would denature completely at high temperature of $72^o$C, hence DNA polymerase is isolated from a thermophilic bacterium Thermus aquaticus.