Microtubules and Motors (Lec. 7) Flashcards
What are the functions of microtubules?
Determine cell shape, involved in cell movement, transport within the cell, and separation of chromosomes during mitosis
Describe the building blocks of microtubules
Tubulin dimers (alpha and beta tubulin) make up protofilaments, which make up microtubules
Describe the GTP/GDP binding at the +/- ends of a microtubule.
At the + end, GTP is bound, which promotes polymerization. At the - end, GDP is bound, which promotes disassembly.
Describe why catastrophe of a microtubule happens
When the rate of GTP hydrolysis to GDP catches up to the rate of tubulin addition, then the GTP cap is lost (because it all turns to GDP), and the microtubule starts depolymerizing.
What are MAPs and what do they do?
Microtubule-associated proteins can bind to microtubules to: increase/decrease growth, restart growth after catastrophe, or help anchor the ends
How are centrosomes relevant to microtubules?
Centrosomes are MTOCs; they anchor the - end and initiate microtubule growth
What does gamma tubulin do?
It acts as the seed for rapid microtubule growth
What do motor proteins do on microtubules? What are the 2 main types of microtubule motor proteins?
They “walk along” microtubules (dynein toward the - end and kinesin toward the + end), transporting cargo, driving cilia and flagella, and orienting the mitotic spindle.
What do primary cilia do?
Sense the environment
What do motile cilia and flagella do?
Move the cell
Describe the structure of a cilia.
9 microtubule doublets are in a circle around a central pair of microtubules (Nexin links all these microtubules together), in an extension of the plasma membrane called an axoneme
Describe the microtubule doublets in a cilium
One is an A tubule, which is complete and normal, and the other is a B tubule, which is incomplete (doesn’t have the regular number (13) of protofilaments)
How do microtubules in a cilium bend?
Dynein and its motor head group are attached to the A tubule of one doublet and the B tubule of another doublet, respectively. The motor head walks along the B tubule toward its - end (the anchor), which causes the thing to bend.
Does dynamic instability increase or decrease during mitosis?
Increase; mitosis requires drastic microtubule rearrangements
What are the three types of microtubules in the mitotic spindle?
Astral microtubules radiate toward the periphery of the cell, interpolar microtubules radiate toward the center, and kinetochore microtubules radiate attach to the centromere of their chromosomes (make metaphase and stuff happen)
What happens during anaphase A?
the kinetochore microtubules shorten through disassembly, pulling the two chromatids apart
What happens during anaphase B?
The interpolar and astral microtubules push the spindle poles apart, using the help of dynein and kinesin.
