Question

Consider two kinesin motor proteins at the mitotic spindle midzone: kinesin A is a tetrameric motor that walks toward the plus end of both microtubules to which it is attached via its motor domains; kinesin B, on the other hand, walks toward the minus end of one microtubule while it is attached to another microtubule via its tail domain.How do these motors affect the length of the spindle?

A. They both work to shorten the spindle.
B. Kinesin-5 works to shorten the spindle whereas kinesin-14 works to lengthen it.
C. Kinesin-5 works to lengthen the spindle whereas kinesin-14 works to shorten it.
D. They both work to lengthen the spindle.

Answer 1

C. Kinesin-5 (kinesin A) works to lengthen the spindle whereas kinesin-14 (kinesin B) works to shorten it.

Step-by-step explanation:

Kinesins are microtubule-based motors localized in the mitotic spindle in order to ensure the correct segregation of the chromosomes during cellular division. These proteins are classified regarding their sequences at the core motor domains which determine their motility. Kinesins can move along microtubules in opposite directions, walking toward the plus end (i.e., the end that grows more rapidly) or moving toward the minus end. Recently, it has been shown that opposite forces between kinesin-5 (plus-end-directed) and kinesin-14 (minus-end-directed) microtubule-based motors regulate the length of the spindle during cellular division. Kinesin-14 is a minus-end-directed motor protein that walks along microtubules from plus- to minus-end, while kinesin-5 is a plus-end-directed motor protein that walks along microtubules from minus- to plus-end, and thereby they work to shorten and lengthen the mitotic spindle, respectively.