Which of the following describes origin licensing in eukaryotes?

• A. RFC clamp loader coordinating PCNA
• B. RPA stabilizing ssDNA
• C. ORC, Cdc6, and Cdt1 loading MCM to license origins
• D. DNA ligase sealing nicks

Answer: (C)

Origin licensing in eukaryotes is the process that prepares origins to start replication in S phase. It happens in G1 when the Origin Recognition Complex (ORC) binds to DNA at origins and, with the help of Cdc6 and Cdt1, loads the MCM2-7 helicase onto the DNA. This loading creates the pre-replicative complex, marking the origin as licensed and able to fire later in S phase when the right signals (CDK and DDK activity)activate the helicase and recruit the rest of the replication machinery. Licensing ensures each origin fires once per cycle, preventing re-replication.

Other options describe different parts of DNA replication or repair: the RFC clamp loader with PCNA is involved in processing DNA during elongation, not licensing; RPA stabilizes exposed single-stranded DNA during replication; and DNA ligase seals nicks during lagging-strand synthesis or repair.