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Mitosis

Problems

Metaphase and Anaphase

Telophase and Cytokinesis

Problem : What is the name of the line along which chromosomes align during metaphase?

The metaphase plate.

Problem : Why is it that metaphase can occupy such a large portion of mitosis?

Alignment of chromosomes along the metaphase plate acts as a checkpoint in the cell cycle. Chromosomes must all be aligned for passage into anaphase. Therefore, a cell will wait in this phase until all chromosomes have aligned. In some cells this can take days.

Problem : What is the signal that triggers the entrance into anaphase?

The deactivation of M phase-promoting factor (MPF) signals the entrance into anaphase. MPF is deactivated by the degradation of the mitotic cyclins that attach to Cdks to form the MPF complex.

Problem : What forces drive the migration of the chromosomes to opposite ends of the cell during anaphase?

Chromosomes are connected to microtubules through their centromere. The structure of microtubules is such that they are constantly being synthesized and degraded at their growing end. During anaphase, the microtubules retract via degradation and pull with them the chromatid that is attached to it.

Problem : What are the events that mark the two distinct phases of anaphase?

During anaphase A, chromosomes attached to microtubules are pulled poleward. During anaphase B, the poles themselves separate as the cell elongates.

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