Final: Ch 18 Mictotubule Structure, Dynamics, Regulation Flashcards
microtubule
stiff tubes that can exist as a single structure, or as a bundled arrangement
generate pushing and pulling forces that allow single tubules to extend long distances, and bundles to slide past each other
tracks for kinesins and dyneins
intermediate filament
have great tensile strength and are like molecular ropes
do not have polarity, and are not used as tracks
microtubules are made of the major protein _____, and associated proteins called…
tubulin, microtubule-assembling proteins (MAPs)
13 longitudinal repeat units called protofilaments
microtubule walls are polarized structures built from….
alpha-beta tubulin dimers
the alpha and beta subunits of tubulin can each bind a molecule of ____
GTP
the GTP is the _____-tubulin subunit is never hydrolyzed, and is trapped inbetween the alpha and beta subunits
alpha
GTP bound by the ____ subunit can be hydrolyzed
beta
binding site is on the surface of the dimer
subunits in microtubules are preferentially added to which end
+ end
which end is which in microtubules
end with beta subunits is +
end with alpha subunits is -
there is polarity
what structures are doublets
cilia, flagella
has an A tubule of 13 protofilaments and a B tubule of 10
what structures are triplets
centrioles, basal bodies
has an A tubule of 13 protofilaments and a B and C tubule of 10
all microtubules are nucleated from structures known as…
microtubule organizing centers (MTOCs)
- end bound to MTOC while + end extends away
centrosome
the main MTOC in animal cells
non-mitotic cells are in what phase
interphase cells
centrosome is located near the nucleus and produces microtubules with + ends radiating toward the periphery
serve as tracks
during mitosis, cells reorganize their microtubules to form a ______ ______ assembled from 2 centromeres to segregate copies of the duplicated chromosomes
bipolar spindle
how are organelles transported along axons
by microtubules
in cilia and flagella, microtubues are assembled from an MTOC called a ____ _____
basal body
centriole
cylindrical structures related to basal bodies
make up centrosomes
surrounded by pericentriolar material
gamma-tubulin ring complex
located in pericentriolar material and is a template that alpha-beta tubulin binds to, to form a new microtubule
- end bound to gamma-tubulin, + end grows
individual microtubules exhibit ______ _______
dynamic instability
polymerization of dimeric alpha-beta tubulin into microtubules is greatly catalyzed by the presence of ____
MAPs
theres are 2 distinct populations of microtubules
those that grow in length
those that shorten rapidly
dynamic instability
the alternation between growing and shrinking states of microtubules
depends on the presence or absence of a GTP-beta-tubulin cap
end of a growing microtubule
has a blunter end and a GTP-beta-tubulin cap
end of a shrinking microtubule
curls like a ram’s horns
has a GDP-beta tubulin cap
why don’t GDP-beta tubulin capped protofilaments attached to an assembled microtubule peel away?
the protofilament-protofilament interactions in the GTP-beta-tubulin are strong enough
how can a disassembling microtubule be rescued to grow
islands of GTP-beta-tubulin on the length of the assembled microtubule
organelle or cell structure capture by the microtubule does what
stabilizes its + end and protects it from a catastrophe
drug colchicine
sequesters all free dimers, resulting in loss of microtubules
relieve joint point/gout (WBC can’t migrate correctly so less inflammation)
functions of microtubule associated proteins (MAPs)
stabilize/destabilize microtubules
crosslink between microtubules (cilia/flagella)
motor proteins
microtubules are stabilized by _____-binding proteins
side
Tau proteins
tau (axons and dendrites), MAP2 (neuron dendrites), and MAP4 (other cell types)
stabilize microtubules and act as spacers
when stabilizing MAPs coat the outer wall of a microtubule, they can ____ the growth rate or suppress the ______ frequency
increase, catastrophe frequency
activity of MAPs is regulated by…
reversible phosphorylation of their projection domains
if phosphorylated, unable to bind microtubules
what kinase is a key modulator of tau proteins
microtubule-affinity-regulating kinase (MARK)
cyclin-depending kinase (CDK)
+TIPs (type of MAP) regulate the properties and functions of the microtubule __ end
+ end
EB1 binds more blunt growing end (+ end)
modifies properties like enhancing polymerization or reducing catastrophes
+TIPs can also link….
microtubule + ends to cell cortex, F-actin, and membranes
other end binding proteins can enhance the frequency of ________, helping to remove tubulin dimers
catastrophes
augmin complex
binds the side of a microtubule and attracts gamma-tubulin ring complex to assemble
what is microtubular protein
alpha-beta tubulin plus microtubule associated proteins
what is a catastrophe
when individual microtubules grow, and then suddenly shrink (rapid depolymerization)
what is a rescue
when a depolymerizing microtubule begins growing again
2 domains of tau proteins
positively charged area that binds negatively charged tubulin surface
2nd domain projects at a right angle from the microtubule
+TIP linkage to the ER transmembrane protein STIM does what
causes microtubule-dependent extension of the ER membrane
kinesin-13
bind tubulin and curve it like GDP-beta-tubulin to facilitate depolymerization
Op18/stathmin
increases rate of catastrophes
enhances hydrolysis of GTP to GDP
what regulates Op18/stathmin
phosphorylation by kinases
