At Which Time Period(s) During PCR Thermocycling Is/are Hottest in Temperature

Question

At which time period(s) during PCR thermocycling is/are hottest in temperature?
A) during DNA denaturation
B) during primer annealing
C) during primer extension/elongation
D) Both the first and last cycles are hotter in temperature than all other cycles.

Accepted Answer

During DNA denaturation, the double-stranded DNA template is heated to high temperatures (usually 95-98°C) to separate the strands. This step requires the highest temperature during PCR thermocycling. During primer annealing and extension, the temperature is lowered to allow for the binding of primers and the extension of the DNA strand. Therefore, the hottest time period during PCR is during DNA denaturation. Option B and C are incorrect as they do not have the highest temperature during thermocycling. Option D is incorrect as there is no evidence to show that the first and the last cycles are hotter in temperature than all other cycles.