Question

Suppose the thermocycler is INCORRECTLY programmed to omit the 72°C step in each cycle of an otherwise normal PCR run. Which of the following would most likely occur?

A. DNA polymerase would synthesize DNA more slowly.
B. DNA polymerase would be active at 94°C.
C. Primers would NOT bind to DNA template strands.
D. DNA template strands would bind to each other.

Answer 1

Omitting the 72°C step in PCR interferes with the Taq polymerase's ability to extend the DNA strands, which would significantly hamper DNA synthesis, leading to incomplete extension and ineffective amplification of the target DNA. Option A is correct.

Step-by-step explanation:

If the thermocycler is incorrectly programmed to omit the 72°C step in each cycle of an otherwise normal PCR run, the enzyme Taq polymerase would not be able to function efficiently since 72°C is the optimal temperature for its activity. This omission would more likely result in incomplete extension or polymerization of DNA strands.

Without this critical extension step, the DNA polymerase would not synthesize the DNA effectively, meaning the PCR would not amplify the target DNA sequences as intended.

In the PCR protocol, each of the temperatures in the cycle is crucial for specific steps - denaturation at around 94°C where the double-stranded DNA is separated, annealing at around 50-60°C where primers bind to the DNA template strands, and extension at 72°C where Taq polymerase adds nucleotides to the primer, extending the DNA strand.

If the 72°C step is skipped, amplification would be inefficient as DNA strands would be left with incomplete or no complementary strands synthesized. Thus, the most likely occurrence, given the options provided, would be that DNA polymerase would synthesize DNA more slowly (Option A), translating to insufficient DNA production and a failed experiment.