[Biology]Orientation of microtubules

[garbagefish]

Homework Statement

1. Because cytoplasmic vesicles are seen to move in both directions in the axon of a nerve cell, can you conclude that some of the microtubules are orientated with their plus-end facing the axon terminus and others orientated with the opposite polarity? Why or why not?

Homework Equations

The Attempt at a Solution

The positive end is designated for the addition of actin subunits, where the ATP-binding cleft of the terminal actin subunit contacts the neighboring subunit (barbed). The negative end is favored for dissociation, where the cleft is exposed to the surrounding solution. Since the cleft is exposed, ATP will bind, hydrolysis of the bound nucleotide reduces the affinity of the subunit for neighboring subunit, and therefore the negative end is favored for dissociation.

 

[Nino MMP]

Given this information, it is reasonable to conclude that some microtubules are oriented with their plus end facing the axon terminus and others orientated with the opposite polarity. This is because microtubules are dynamic structures with the ability to grow and shrink in either direction. Therefore, it is possible for microtubules to be orientated in both directions depending on the environment and energy input.

 

[Blueshift5]

I cannot conclusively determine the orientation of microtubules based solely on the observation of cytoplasmic vesicle movement in a nerve cell. While it is possible that some microtubules may be oriented with their plus-end facing the axon terminus and others with the opposite polarity, there are other factors that could also influence the direction of vesicle movement, such as motor proteins and cellular signaling. Further experiments, such as labeling and tracking individual microtubules, would be necessary to accurately determine their orientation.