Which checkpoint pathways monitor replication fork integrity and coordinate cell cycle progression?

• A. ATM-Chk2 and BRCA1-Chk1 pathways
• B. ATR-Chk1 responds to replication stress and ATM-Chk2 to double-strand breaks
• C. p53-Chk2 axis
• D. CDK-Cyclin checkpoints

Answer: (B)

The main idea is that cells use two interconnected checkpoint pathways to sense problems during DNA replication and to coordinate how the cell cycle progresses. When replication runs into stress and forks stall, the ATR-Chk1 axis is activated. ATR detects the presence of exposed single-stranded DNA coated with RPA at stalled forks and activates Chk1, which then slows or halts the cell cycle and helps stabilize the fork so repair can occur. This pathway specifically monitors replication integrity and keeps replication on track with proper timing. On the other hand, when there are actual double-strand breaks, the ATM-Chk2 pathway takes the lead, initiating repair processes and contributing to cell cycle arrest as needed. Together, this pairing—ATR-Chk1 for replication stress and ATM-Chk2 for breaks—best explains how replication fork integrity is monitored and how cell cycle progression is coordinated in response to different kinds of DNA damage. The other options either point to downstream or broader cell-cycle regulators or mix in components not primarily described as the fork integrity checkpoint.