Chapter 13 - Microtubules

a microtubule is a ploymer made of

αβ-tubulin heterdimers

α-tubulin binds __________ irreversibly and does not hydrolyze it

GTP

β-tubulin hydrolyzes __________ to __________ after incorporation into microtubules

GTP, GDP

Each protofilament in a microtubule has intrinsic ________

polarity making the MT itself polar

The minus end of a microtubule is capped with

α-tubulin

The plus end of a microtubule is capped with

β-tubulin

Polymerization only occurs if tubulin concentration is __________ the critical concentration

above

The three phases of microtubule assembly are __________, __________, and __________

nucleation, elongation, steady state

nucleation is the formation of a ‘nucleau’ which can

elongate to form a microtubule

elongation is when subunits

add onto the nuclei leading to filament growth

when the Cc is reached the reaction goes into steady state is when there is no

net increase or decrease in the amount of polymerized microtubules

Microtubule polymerization is favored in cells because the tubulin concentration is __________ than the Cc

much higher

The __________ cap stabilizes the plus end of the microtubule

GTP

Loss of the GTP cap leads to a rapid depolymerization event called ___

Catastrophe

Regrowth of a microtubule after shrinkage is known as ________

rescue

The behavior where MTs rapidly grow and shrink is called __________ __________

dynamic instability

In cells, microtubules grow out from a structure called the __________

microtubule organizing center (MTOC)

The protein complex that nucleates MTs at the MTOC is the __________

γ-TURC (gamma-tubulin ring complex)

γ-tubulin does not polymerize but helps in microtubule ________

nucleation

__________ stabilizes microtubules and prevents disassembly

taxol

__________ binds to tubulin and blocks further polymerization, promoting disassembly

colchicine

__________ is a synthetic compound that causes MT depolymerization

nocodazole

microtubules function in cell

polarity, membrane trafficking, and mitosis