Microtubules Flashcards
Microtubules
long hollow cylinders made of protein tubulin
long straight and typically have one end attched to a single microtubule organizing center (MTOC aka centrosome)
Targeted by cancer drug taxol
Microtubules function
Centrosome vesicle movement signal transduction
Cilia (sensory and motile)
Cell division (mitotic spindle)
Microtubule structure
protofilament of repeating alpha and beta tubulin. Plus end by Plasmamembrane
Can rapidly shorten and elongate (dynamic instability)
Assembly and dissassembly of microtubules
Tubulin structure exists as a heterodimer (the beta subunit binds to GTP to polymerize)
GDP-> conformational change-> dissassembly
Mediated by the GTP cap (if capped it allows rescue/growth) if the cap falls off–> catastrophe and the protofilament shortens
Initiation of microtubule assembly centrosome MTOC
gamma tubulin is on the outside of the centrosome and the alpha and beta add on to it
Centrosome: made of centrioles that organize an amorphous assembly of proteins called the pericentriolar material
centrioles are inside and are in l shaped manner, nine fold riplet symmetry (one complete A microtubule with two incomplete B and C microtubules)
Microtubule organization of Cilia
Cilia are specialized structures that are built from microtubules
hairlike structures, found on most cells with whip like motion, can be sensory or structural
Axoneme: arises from the basal body which is a centriole (9x2 +2 complete)
Microtubule based molecular motors
Dynein (short) and kinesin(long)
Kinesin goes in the plus direction
Dynein goes in the minus direction
Mitotic spindle at metaphase
mitotic spindle is an array of microtubules, centrosomes duplicate when the cell duplicates
Kinetochore microtubules attach chromatids to opposited poles of spindle (there is a zone of interdigitation)
Astral microtubules (radiate outward and help position spindle in cell)
Kinesin push and pull
