Which statement describes the difference between origin licensing and firing?

Which statement describes the difference between origin licensing and firing?

• A. Licensing occurs during S phase; firing in G1.
• B. Licensing occurs to prepare origins during G1; firing is the actual initiation of replication at licensed origins during S phase.
• C. Licensing occurs in G2 to repair.
• D. Licensing is not necessary.

Answer: (C)

Origin licensing is the preparatory step in G1 where replication origins are readied by loading a helicase complex so those sites are allowed to start replication. Firing is the actual initiation of DNA synthesis at those licensed origins, and it happens during S phase when replication begins. This separation is crucial because licensing marks origins as eligible to fire, and firing activates them to begin copying DNA, ensuring each origin fires at most once per cell cycle. Licensing in G2 wouldn’t fit the purpose, since the goal is to prepare for the upcoming S phase and prevent re-replication; the idea that licensing is for repair isn’t correct, because licensing is specifically about preparing origins for replication, not repairing DNA.

Origin licensing is the preparatory step in G1 where replication origins are readied by loading a helicase complex so those sites are allowed to start replication. Firing is the actual initiation of DNA synthesis at those licensed origins, and it happens during S phase when replication begins. This separation is crucial because licensing marks origins as eligible to fire, and firing activates them to begin copying DNA, ensuring each origin fires at most once per cell cycle. Licensing in G2 wouldn’t fit the purpose, since the goal is to prepare for the upcoming S phase and prevent re-replication; the idea that licensing is for repair isn’t correct, because licensing is specifically about preparing origins for replication, not repairing DNA.