Questions: The polymerase chain reaction requires one specific DNA oligonucleotide as a primer. single-stranded DNA as template. cyclical denaturation and annealing of double-stranded DNA.

The answer is the fourth one: cyclical denaturation and annealing of double-stranded DNA.

Explanation for each option:

1. Primase: Incorrect. Primase is an enzyme that synthesizes RNA primers in vivo during DNA replication, but it is not required for PCR. PCR uses DNA primers instead.

2. One specific DNA oligonucleotide as a primer: Incorrect. PCR requires two specific DNA oligonucleotides as primers, one for each strand of the DNA template, to initiate DNA synthesis.

3. Single-stranded DNA as template: Incorrect. PCR typically starts with double-stranded DNA as the template. The process involves denaturing the double-stranded DNA to single strands, which then serve as templates for replication.

4. Cyclical denaturation and annealing of double-stranded DNA: Correct. PCR involves repeated cycles of denaturation (separating the DNA strands), annealing (binding of primers to the single-stranded DNA), and extension (synthesis of new DNA strands).

5. A heat-resistant RNA polymerase: Incorrect. PCR requires a heat-resistant DNA polymerase, such as Taq polymerase, which can withstand the high temperatures used during the denaturation step.

In summary, the polymerase chain reaction requires cyclical denaturation and annealing of double-stranded DNA.