University Of Central Florida (UCF) PCB3023 Molecular Cell Biology Practice Exam 4

Cells use a variety of mechanisms to ensure that DNA replication is completed before entering mitosis, which is critical for maintaining genomic integrity. If DNA replication is incomplete, one of the key regulatory actions involves the inhibition of Cdc25 phosphatase. Cdc25 is responsible for removing inhibitory phosphates from the M-Cdk (cyclin-dependent kinase), leading to its activation and promoting the transition into mitosis. When Cdc25 is inhibited, M-Cdk remains inactive, thereby preventing the cell from advancing into mitosis. This delay allows additional time for DNA replication to finish, ensuring that the cell does not enter mitosis with damaged or incomplete genetic material. Thus, the inhibition of Cdc25 serves as a checkpoint mechanism that safeguards the integrity of the cell's genetic information by linking the completion of DNA replication to cell cycle progression. In contrast, while the inactivation of S-Cdk complexes, the lack of APC/C activation, and starting a new round of DNA replication are all concepts related to cell cycle regulation, they are not the primary mechanisms for delaying entry into mitosis specifically due to incomplete DNA replication. The focus here is on how the cell uses the inhibition of Cdc25 phosphatase as a critical control point in the cell cycle