Question

A biology student is performing PCR for the first time. She adds the right DNA fragments and its corresponding primers. She also adds DNA polymerase and free nucleotides. The reaction mixture is kept in a water bath that measures ${37}^{\circ }C$. But DNA amplification does not occur. Why?

• A. Thermocycler was not used to maintain temperatures required for PCR
• B. DNA primers got denatured at ${37}^{\circ }C$
• C. She added DNA polymerase instead of RNA polymerase
• D. Not enough DNA Fragments were available for the DNA polymerase to act on.

Answer 1

The correct option is A Thermocycler was not used to maintain temperatures required for PCR

For PCR a thermocycler is required, which provides the optimum temperatures required for the three different steps in PCR- denaturation, annealing and extension. Denaturation involves the breaking of hydrogen bonds and requires a very high temperature. A lower temperature between 40 - 60 degree celcius is required for the primers to anneal and extension happens at a a different temperature than annealing temperature. By placing the reaction vessel in a constant temperature water bath, the PCR process will not get activated.