Question

Which of the following is NOT a required component of a polymerase chain reaction (PCR)?

A) deoxynucleotides

B) two primers

C)DNA ligase

D)heat stable DNA polymerase

E) none of the above (i.e. all the above are required components of a PCR)

E)

Answer 1

The right answer is option (C) DNA ligase

Explanation :-

Deoxynucleotides are required for the PCR as they are the building blocks of DNA. DNA is synthesized by polymerising them together with the help of DNA polymerase. Since we carry out PCR in vitro, it means we have to add them separately.

Two types of primers are used in PCR. They are called Forward and reverse primers. The forward primer attaches to the 5' end of the template DNA while the reverse primer attaches to the 5' end of the complementary strand of DNA.

Heat stable DNA polymerase is needed for PCR because the temperature of PCR reaction goes up to 95°C and proteins (enzymes) will be degraded from normal cells. Thus they are taken from those species which live in hot areas like hot spring.

DNA ligase isn't needed for the PCR because there are no Okazaki fragments which needs to be ligated as each strand have a continuous synthesis unlike how it happens in a cell where one strand is synthesized continuously while the other is created in short fragments which are then ligated together with the help of DNA ligase. Since this doesn't happen in a PCR reaction, there's no need for ligase enzyme.