Final answer:
Replication Licensing Factors (C) are essential for ensuring that each segment of eukaryotic DNA is replicated exactly once in each cell cycle by licensing the origins of replication before the S phase.
Step-by-step explanation:
The proteins that are directly responsible for ensuring that eukaryotic DNA is replicated precisely once in each round of replication are Replication Licensing Factors (C). These factors play a critical role in the initiation phase of DNA replication. Before replication begins in eukaryotes, a pre-replication complex is formed at the origin of replication with other initiator proteins. Replication Licensing Factors are necessary to ensure that the DNA is replicated once and only once. This avoids re-replication of the same stretch of DNA within one cell cycle.
Helicases, single-strand binding proteins, DNA polymerases, and many other enzymes and proteins participate in the unwinding of DNA and its replication. However, it is the Replication Licensing Factors that set the stage for the replication process by 'licensing' an origin of replication before the cell enters into the S phase of the cell cycle, ensuring that each segment of the genome is prepared for replication.