A researcher prepares a standard Polymerase Chain Reaction (PCR) mixture but mistakenly adds normal human DNA polymerase instead of Taq polymerase isolated from Thermus aquaticus. The mixture is then subjected to a standard thermal cycle: 94^ C for 1 minute, 55^ C for 45 seconds, and 72^ C for 1 minute. Which specific step of the first PCR cycle will fail to produce its intended molecular outcome?

Step-by-step solution

The first step of the PCR cycle is denaturation at 94^ C , which relies solely on heat to break the hydrogen bonds between DNA strands. This step will occur successfully. However, normal human DNA polymerase is not thermostable and will be irreversibly denatured (destroyed) by this high temperature. The second step, annealing at 55^ C , also occurs successfully because primers hybridize to the template DNA based on complementary base pairing, which does not require an enzyme. The third step, extension at 72^ C , re