Question

One of the most remarkable features of the cell-cycle control system is that a single protein complex, _____, brings about all the diverse and intricate rearrangements that occur in the early stages of mitosis. _____ helps prepare the duplicated chromosomes for segregation and induces the assembly of the mitotic spindle- the machinery that will pull the duplicated chromosomes apart. M-Cdk complexes accumulate throughout _____ but are not activated until the end of G2, when the activating phosphatase _____ removes the inhibitory phosphate holding M-Cdk activity in check.

Answer 1

The protein complex that brings about various processes in the early stages of mitosis is the Mitotic Cyclin-Cdk complex (M-Cdk), which is activated at the end of the G2 phase by the phosphatase Cdc25.

Step-by-step explanation:

The single protein complex mentioned in the student’s question is the Mitotic Cyclin-Cdk complex, commonly referred to as M-Cdk. The M-Cdk complex is crucial for the early stages of mitosis, facilitating chromosome condensation and the assembly of the mitotic spindle that separates duplicated chromosomes. M-Cdk complexes accumulate throughout interphase but become activated at the end of the G2 phase. The activation occurs when the activating phosphatase, which is Cdc25 according to relevant literature, removes an inhibitory phosphate that was preventing M-Cdk activity.

This regulatory mechanism is part of the cell-cycle control system, which ensures proper replication and separation of chromosomes as a part of cell division. In the broader context of the cell cycle, different cyclin-Cdk complexes function at various points to regulate progression through checks such as the G1, G2/M transition, and metaphase checkpoints. Errors in the regulation of these processes can lead to issues like cancer, characterized by uncontrolled cell division.