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31 Cards in this Set

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microtubules siz
largest (25nm)
hollow tube
intermediate filaments size
medium (8-12 nm)
microfilaments ( actin filaments) size
smallest (7 nm)
Microtubule subunit
subunit: tubulin heterodimers (alpha and beta subunits)
heterodimer->protofilament
->microtublue
Dynamics of microtubules
Cytoplasmic microtubules (provide structure & organiz., track for transport, seperate chromosomes during mitosis/meisos) are dynamic, axonemal microtubules (movement of flagella and cilia) aren't
how do micro tubules grow and shorten?
lag phase: individual dimers
elongation phase: growth
Plateau phase: treadmilling, net growth = 0 (really only an in vitro phase)
rapid shortening in microtubles
catastrophe
rapid growth after rapid shortening
(microtubules)
rescue
What determines the growth or shortening of microtubules?
GTP vs GDP concentration, GTP bound heterodimers have a greater affinity than GDP bound heterodimers
if GTP cap is lost, m.t. catastrophe occurs
microtubules provide
shape and polarity
ex. both important in nerve cells
Microtubule Organizing Center
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
centrosome
pair of centriolds made up of triplet microtubules. (star formation)
Gamma tubulin
located at MTOC, changes kinetics, promotes microtubule growth
MAPS (microtubule associated proteins)
Tau (binds to side of mt and stabilizes it, reduces dyanmics) ,+TIPS (binds to + end, promotes elongation), and catastrophin (rapidly shortens)
Microtubule motors:
kinesins and dynein
two headed motors, go toward - end, use ATP hydrolysis to move
Kinesin
have similar motor domains, 14 subtypes, KinI Kinesins destabilize MTs
most move to + end
Vesicle transport between ER and gogli apparatus
utilizes MTS and motor proteins
Axoneme structure
9+2 array (9 circle couples things in a circle around 2 circles in the middle)
Axonemal Dynein
3 headed motor, sliding filament model (ex. sperm)
Intermediate filaments
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
Composition of intermediate filaments
Keratin in epithelial cells
vimetin in fibroblasts
desmin in muscle cells
neurofilaments in neuron
nuclear lamsins
Actin filaments (microfilaments)
made of actin monomers
F actin binds ATP, which reduces to ADP after polymerization
Polar
Actin polymerization
Nucleation--> elongation --> steady state

formation of trimer is rate-limiting
functions of actin filaments
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)
myosin powerstroke
moves actin filaments
Muscle contraction
Thick filaments constant, thin filaments move
H zone decreases, A zone constant, Z lines come closer, sarcomere shortens, I band shortens
Non muscle motility
depends on actin filament polymerization
cell cortex
dense layer of contractile proteins beneath the plasma membrane
Cytoplasmic Dynein
motion toward minus end of microtubule
axonemal dynein
activation of sliding in flagellar microtubule
kinesin
motion toward plus end of microtubule