Question

When a cell has stalled DNA replication fork which checkpoint should be predominantly activated?

Answer 1

The replication fork is the region of DNA where the replication process takes place. Its structure is similar to that of a fork. At the replication fork, there is a multiprotein complex that performs replication. Helicase unwinds DNA strands in front of the fork, resulting in two single DNA strands that resemble the fork's branching "prongs". Using single-stranded DNA templates, DNA polymerase creates the new leading and lagging strands. As DNA replication continues, the replication fork shifts.

Complete answer:
Cell cycle checkpoints ensure that the cell only moves on to the next phase when the previous one has been fully completed. During S-phase, a DNA replication checkpoint ensures that genome stability is maintained. The cell cycle is halted at $G1$ before replication begins or in the $G2$ phase before mitosis when DNA is damaged excessively. Damages connected with replication forks cause the S phase to be delayed. The cell cycle is controlled by cyclin-dependent kinases. They attach to particular cyclins and phosphorylate various proteins, causing some enzymes to activate and others to deactivate. $G1$-Cdk helps the cell transition from the $G1$ to the S phase.

Note:
DNA replication is a complicated process that occurs during cell division (interphase, S phase), in which DNA replicates before the cell divides during mitosis and meiosis.
DNA replication is a semiconservative process in which multiple protein elements, such as enzymes and RNA molecules, are employed to synthesize a new complementary daughter strand from a parental strand.
The key enzyme in the DNA replication process is DNA polymerase, which catalyses the joining of deoxyribonucleoside $5\prime$-triphosphates (dNTPs) to produce an expanding chain of DNA.
Other proteins are involved in the replication process' start and DNA copying, as well as proofreading capabilities to guarantee that the process is carried out correctly.