FIGURE 14.33 Proposed activity of motor proteins during mitosis. (a) Prometaphas

Question

FIGURE 14.33 Proposed activity of motor proteins during mitosis. (a) Prometaphase. The two halves of the mitotic spindle are moving apart from one another to opposite poles, due to the action of bipolar (four- headed) plus-end-directed motors (members of the kinesin-5 family). These motors can bind by their heads to antiparallel microtubules from opposite poles and cause them to slide apart (step 1). (Additional motors associated with the centrosomes and cortex are not shown.) Meanwhile, the chromosomes have become attached to the chromosomal microtubules and can be seen oscillating back and forth along the microtubules. Ultimately the chromosomes are moved to the center of the spindle, midway between the poles. Poleward chromosome movements are mediated by minus-end- directed motors (i.e., cytoplasmic dynein) residing at the kinetochore

Explanation / Answer

Answer :-

Superimposed on the global and local regulation of microtubules are the microtubule movements driven by motor proteins.

Steps

1) : Interpolar microtubule - antiparallele microtubules that originate from opposite poles and overlap at the mid zone of the spindle.

2) Microtubule just miss the kinetochore, but the kinetochore bind to the side of microtubules and then slides to (+) ends.

3) non-kinetochore microtubules can exert a pushing force on the chromatid arm of a chromosome by polymerization at their (+) ends.

4) Coordinated motar and microtubule depolymerase activity of kinesin at spindle poles.

5) Amphitelic ( bi-orientation) sister kinetochore attached to opposite poles.

6) Depolymerization at both ends during chromatid segregation.

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