Microtubules, Dynamic Instability and the Spindle
Microtubules switch between growth and rapid shortening. These changes help spindle microtubules explore space and attach to chromosome kinetochores. Continued dynamics also support attachment correction and chromosome movement.
What a learner can do afterwards
- Describes dynamic instability as switching between growth and rapid shrinking, and says what triggers the switch.
- Explains how microtubule growth and shortening support search and capture at chromosome kinetochores.
- Predicts how suppressing microtubule dynamics can impair spindle function and cell division.
1 · Read
Like actin, microtubules have plus and minus ends. They contain tubulin pairs; spindle plus ends usually explore outward from the poles. Dynamic instability is switching between growth and rapid shortening. New tubulin helps maintain a stabilizing GTP-rich tip cap during growth. Cap loss favors catastrophe, the switch to shortening. Rescue is a switch from shortening back to growth.
DNA replication produces two sister chromatids per chromosome, one for each daughter cell in mitosis. Spindle poles lie on opposite sides. A kinetochore is a protein complex assembled at a chromatid's centromere. It provides the usual end-on spindle microtubule attachment. Capture can maintain attachment while the microtubule gains or loses subunits. Attachments need checking and correction so sisters connect to opposite poles and separate into different daughter cells.
Growing microtubules sample space near chromosomes. An unattached end may shorten and later grow again. Repeated trials help establish attachments without aiming every end at a known target. Search and capture is part of spindle assembly, not the whole process. Chromosome-associated signals and other mechanisms also influence where microtubules form and attach.
A drug that strongly suppresses microtubule growth and shortening can impair searching, attachment correction and chromosome movement. Division may stall or chromosomes may separate incorrectly. Existing attachments do not all disappear, and some new contacts may still occur. Completing initial attachment does not remove the later need for spindle dynamics.
Cap loss favors catastrophe; rescue restarts growth. Search and capture helps establish kinetochore attachments, and continued dynamics support spindle function.
Lesson, questions and flashcards written for this dataset.
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