Nota Terkini

Tuesday, June 16, 2009

[Biology Form 4] Phases Of Cell Cycle And Mitosis - Metaphase

As microtubules find and attach to kinetochores in prometaphase, the centromeres of the chromosomes convene along the metaphase plate or equatorial plane, an imaginary line that is equidistant from the two centrosome poles.

This even alignment is due to the counterbalance of the pulling powers generated by the opposing kinetochores, analogous to a tug-of-war between people of equal strength.

In certain types of cells, chromosomes do not line up at the metaphase plate and instead move back and forth between the poles randomly, only roughly lining up along the midline. Metaphase comes from the Greek μετα meaning "after."

Because proper chromosome separation requires that every kinetochore be attached to a bundle of microtubules (spindle fibres), it is thought that unattached kinetochores generate a signal to prevent premature progression to anaphase without all chromosomes being aligned. The signal creates the mitotic spindle checkpoint.

A cell in late metaphase. All chromosomes (blue) but
one have arrived at the metaphase plate.


Metaphase: The chromosomes have
aligned at the metaphase plate.

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