Interaction of microtubules and the mechanism of chromosome movement (zipper hypothesis). 3 Theoretical analysis of energy requirements and computer simulation of chromosome movement.

A theoretical analysis of the energy requirements and a computer analysis of a special case (symmetrical pull in one plane during anaphase), of the zipper model for chromosome movement (Bajer, 1973a,b) is presented. The conclusions are general, however, and can be applied to any stage of mitosis. It is assumed that the movement is due to a series of short lateral interactions (called 'zips') between microtubules, and it is shown that a particular zip could begin if the bending energy requirement for two microtubules is met, and could terminate when a strain restriction is exceeded. The series of zips ends when the energy requirements for initiation of a particular zip are not met. In such conditions, certain predictions concerning the behaviour of microtubules in the spindle can be made (see Conclusions). It is shown that hydrolysis of ATP or GTP can yield sufficient energy to bend microtubules as specified by the model, that insignificant quantities of the triphosphate would be utilized, and that the linearity of chromosome movement predicted by the model is consistent with the linearity observed in vitro.