Question

when performing PCR (polymerase chain reaction), how is the double stranded DNA split into two single stranded DNA molecules?

a) high temperatures

b) the action of helicase

c)the action of dna polymerase

d) the action of Taq polymerase

Answer 1

ANSWER: OPTION- A [HIGH TEMPERATURES]

Explanation:

The Polymerase Chain Reaction (PCR) is an advanced technology that uses four deoxyribonucleotides, primer, target DNA and Taq polymerase to make large quantities of the target DNA. Polymerase Chain Reaction has three steps that are repeated as many times till we get the DNA amplified. The repeated cycles are carried out in order to amplify the DNA. The three steps are:

· Denaturation

· Renaturation

· Synthesis

Denaturation: The PCR starts with this step; in denaturation the temperature is raised to about 95°C. At this high temperature the double stranded DNA gets denatured into two separate single stranded DNA. This temperature is maintained about 1 minute.

Renaturation/Annealing: This step is called as renaturation because after denaturation of the DNA the temperature is slowly lowered to about 55°C, now the primers get paired to the complementary sites of the single stranded DNA. The pairing with the primer occurs at this temperature.

Synthesis: This is the final step in PCR cycle. Now the temperature is raised from 55°C to about 72°C. The Taq DNA polymerase is only active at 72°C. So at 72°C it starts to synthesis the DNA from the primer site by adding deoxyribonucleotides properly. After the DNA is synthesised the temperature is slowly increased to 95°C so the second cycle starts. And at this high temperature the DNA is denatured and all the process is repeated.