(2) You have allowed microtubules to polymerize in vitro under conditions where

Question

1. (2) You have allowed microtubules to polymerize in vitro under conditions where you observe individual microtubule dynamics (e.g. using fluorescently-labeled tubulin and observing the microtubules on a fluorescence microscope). What happens to the newly exposed ends if you sever a microtubule with a high powered laser (to completely sever the microtubule, not just “nick” or damage it)? Why does this happen?

1. (2) You have allowed microtubules to polymerize in vitro under conditions where you observe individual microtubule dynamics (e.g. using fluorescently-labeled tubulin and observing the microtubules on a fluorescence microscope). What happens to the newly exposed ends if you sever a microtubule with a high powered laser (to completely sever the microtubule, not just “nick” or damage it)? Why does this happen?

Explanation / Answer

Microtubules are formed by polymerization of the dimer of alpha tubulin and beta tubulin. The microtubules are always polar that means its alpha tubulin end always bind a beta tubulin end and so on. So in a microtubule one end always have the Alpha tubulin exposed (-end) and one end always beta tubulin exposed (+end). The microtubules always grow towards + end.

Now both the tubulin is joined with GTP. When polymerization starts one dimer unit (GTP-ALPHA-BETA-GTP) bins with another dimer at its beta or positive end. After this attachment the GTP bound to Beta tubulin hydrolyzes to form GDP.

So the structure becomes

(GTP)ALPHA-BETA(GDP)-(GTP)ALPHA-BETA(GDP)-(GTP)ALPHA-BETA(GDP)-(GTP)ALPHA-BETA(GTP)

Now when at the end a new (GTP)ALPHA-BETA(GTP) is present the microtubule remains stable which is known as GTP cap.

If you sever a microtubule using laser beam it is most likely a + end will be exposed which is a GDP bound Beta tubulin. This causes breakdown of the filament causing depolarization because of lesser structural stability of GDP carring structures. So the microtubule will shrink.

Related Questions

Navigate

• Browse (All)
• Browse #
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.