Thursday, November 13, 2008

Scientific Inquiry about Microtubules

Although both ends of a microtubule can gain or lose subunits, one end (called the plus end) polymerizes and depolymerizes at a higher rate than the other end (the minus end). For spindle microtubules, the plus ends are in the center of the spindle, and the minus ends are at the poles. Motor proteins that move on microtubules specialize in walking either toward the plus end or toward the minus end; the two types are called plus end-directed and minus end-directed motor proteins. Given what you know about chromosome movement and spindle changes during anaphase, predict which type of motor proteins would be present on (a) kinetochore microtubules and (b) nonkinetochore microtubules.

Mrs. Lyon (a drawing would help you)


Ruby said...

When a motor molecule carrying a chromatid is attached to the kinetochore microtubule it is traveling from the plus end of the microtubule (the center of the spindle) to the minus end (one of the poles). And so because of this I would guess that the motor protein traveling on the kinetochore microtubule is minus end-directed and the motor molecule traveling on non-kinetochore microtubule is plus-end directed.

Plus end-directed motor molecules contain both dynactin and kinesin-2. Minus end-directed motor molecules contain both dynactina and dynein.

Here is the HTML of the picture that I referenced.

Ruby said...

Sorry I meant that minus end-directed motor molecules contain both dynactin (not dynactina) and dynein.

And the minus-end directed molecules are located on the kinetochore microtubules because they are degrading the microtubule as they travel (with one of the two sister chromatids) back to the centrosomes. (just to clarify some of what i said..)

WhitHar said...

(a) During anaphase, the chromatid moves toward the spindle pole, the negative end, and away from the center, the positive end. The microtubules near the center (plus end) depolymerize faster. I would guess that this is because the motor protein is on the plus end, moving with the chromatid to the minus end as it degrades the microtubule. Therefore, it would be minus-end directed.

(b) The plus-end directed motor proteins move from the minus end to the plus end of the microtubule on the nonkinetochores. This would be because during anaphase, the kinetochores shrink while the nonkinetochores lengthen. As the motor protein moves from the spindle to the center, it is able to add units onto the microtubule therefore allowing it to grow.

Here's a link to the image that I used.

HannahMontana said...

(a) During the anaphase stage of mitosis, the replicated centromeres (microtubule organizing structures) separate and the sister chromatids move away from each other towards opposite poles of the cell by the mitotic spindle. the kinetochore microtubules shorten and break down in this process. They have an affinity for the negative end at the poles, moving away from the center which is the positive end. the positive end depolymerizes at a faster rate and because the dynein motor protein is present on the positive end and moves towards the negative end, the motor protein is minus-end directed.

Note: there are two distinct sets of motor proteins: one of these pulls overlap microtubules past each other, the other pulls on astral microtubules that have attached to the cell cortex.

(b) During anaphase, the nonkinetochores lengthen and push the centrosomes, and the set of chromosomes to which they are attached, apart to opposite ends of the cell. So the plus-end directed motor proteins move from the negative end (poles) to the positive end (in the center) of the nonkinetochore microtubules.

Images I used:

Here is just a cool picture of a motor protein:

Kicki said...

During Anaphase, the sister chromatids separate and move toward the poles of the cell. As they are traveling toward the poles, or the minus end of the cell, there are motor proteins that depolymerize the plus end of the cell. These proteins break down the microtubules attached to the kinetochore region of the sister chromatids. At the same time, the nonkinetochores are lengthening. Thus, I think that kinetochores are minus-end directed, as they shorten and move to the minus end of the cell. On the other hand, I think that the nonkinetochores are plus-end directed, as they grow into the middle of the cell, or the plus-end.

Kicki said...

I found these websites really helpful: