Question

Expand PCR. How does it help in the amplification of the gene of interest?

Answer 1

Hint: At times we only have a small piece of DNA. Thus a sample is not enough to work on. Therefore, there are various techniques which are used to amplify or clone the DNA strand. One such fast method to clone the DNA strand is PCR. It creates multiple DNA copies in less time.

Complete answer:
To solve the question we must know about PCR.
PCR stands for polymerase chain reaction. This technique was developed by Kary Mullis.
PCR has three important steps:
> Denaturing of the DNA strand
> Annealing of the DNA
> Extension of the chain

> Denaturing of the DNA strand – Denaturing simply means that the double stranded DNA strands are changed to the single stranded DNA. This is done by increasing the temperature to 92-95ᵒC for 1 minute.
> Annealing of the DNA strand- The temperature is again lowered to 45-65ᵒC. This helps in attaching the primer to the DNA strand, a process known as hybridization or annealing. These primers act as the starting point for the enzyme DNA polymerase to act.
> Extension - This is the last step in the PCR. The temperature is again increased to 65-75ᵒC. During this step the enzyme DNA polymerase adds new complementary nucleotides to the new strands.

Each cycle takes 2-3 minutes to create a copy of the DNA. The entire process is completed in the thermal-cyclers also known as the PCR machine.

Note: Here it must be noted that the Polymerase Chain Reaction has several other disadvantages too. The exact sequence of the target DNA must be known. There must be no contamination in the sample DNA otherwise there will be a problem in cloning. Further, if the sample is too large then the PCR is not possible.