Ch 15

largest (25nm)
hollow tube

medium (8-12 nm)

smallest (7 nm)

subunit: tubulin heterodimers (alpha and beta subunits)
heterodimer->protofilament
->microtublue

Cytoplasmic microtubules (provide structure & organiz., track for transport, seperate chromosomes during mitosis/meisos) are dynamic, axonemal microtubules (movement of flagella and cilia) aren't

lag phase: individual dimers
elongation phase: growth
Plateau phase: treadmilling, net growth = 0 (really only an in vitro phase)

catastrophe

rescue

GTP vs GDP concentration, GTP bound heterodimers have a greater affinity than GDP bound heterodimers
if GTP cap is lost, m.t. catastrophe occurs

shape and polarity
ex. both important in nerve cells

mtoc's nucleate microtubules, they stimulate formation so they grow more rapidly, directs growth at a particular location. the minus end is anchored to the MTOC
Ex. centrosome and basal bodies

pair of centriolds made up of triplet microtubules. (star formation)

located at MTOC, changes kinetics, promotes microtubule growth

Tau (binds to side of mt and stabilizes it, reduces dyanmics) ,+TIPS (binds to + end, promotes elongation), and catastrophin (rapidly shortens)

kinesins and dynein
two headed motors, go toward - end, use ATP hydrolysis to move

have similar motor domains, 14 subtypes, KinI Kinesins destabilize MTs
most move to + end

utilizes MTS and motor proteins

9+2 array (9 circle couples things in a circle around 2 circles in the middle)

3 headed motor, sliding filament model (ex. sperm)

1.) only in multicellular organisms
2.) IFs conver mechanical strength on tissues, found @ cell/ cell junctions called desmososomes and cell ECM junctions called hemidesmosomes
3.) comp. depends on cell type
4.) nonpolar, most stable filament of cytoskeleton, holds tissues together

Keratin in epithelial cells
vimetin in fibroblasts
desmin in muscle cells
neurofilaments in neuron
nuclear lamsins

made of actin monomers
F actin binds ATP, which reduces to ADP after polymerization
Polar

Nucleation--> elongation --> steady state

formation of trimer is rate-limiting

1.) muscle contraction
2.) cell movement (migration by lamellapodia extension)

3,) cell shape & adhesion (cell cortex, microvilli, stress fibers)
4.) intracellular processes (phagocytosis, cytokenesis, movement of vesicles and organelles)

moves actin filaments

Thick filaments constant, thin filaments move
H zone decreases, A zone constant, Z lines come closer, sarcomere shortens, I band shortens

depends on actin filament polymerization

dense layer of contractile proteins beneath the plasma membrane

motion toward minus end of microtubule

activation of sliding in flagellar microtubule

motion toward plus end of microtubule