Final answer:
The event that does not occur in a single cycle of PCR is the D. addition of dideoxynucleotides, which is a step used in Sanger sequencing for terminating DNA strand elongation.
Step-by-step explanation:
Events in a Single Cycle of PCR
In the Polymerase Chain Reaction (PCR), several key events occur in each cycle: denaturation of the DNA, annealing of the primers, and synthesis of complementary strands. However, the addition of dideoxynucleotides is an event that does not occur in a single cycle of PCR. Dideoxynucleotides are specifically used in Sanger sequencing to terminate DNA strand elongation, which is a different process from PCR. In PCR, the aim is to exponentially amplify a segment of DNA, not to read its sequence.
Thus, common PCR steps include a) pulling apart the two DNA strands (denaturation), b) attaching complementary nucleotides to the template strand (extension or synthesis), but not d) adding dideoxynucleotides, which is associated with DNA sequencing.
SUMUP of the final answer: