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cell and molecular > 11.6-11.11 > Flashcards

11.6-11.11 Flashcards

1
Q

true or false: dynamic instability is a non-equilibrium process

A

true

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2
Q

what drives dynamic instability

A

GTP hydrolysis by tubulin

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3
Q

during assembly, B-tubulin is stimulated to do what?

A

hydrolyze bound GTP to GDP

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4
Q

is GTP hydrolysis or polymerization faster

A

polymerization

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5
Q

does a growing microtubule have mostly GDP or GTP B tubulins

A

GDP

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6
Q

true or false: a tubulin always has GTP

A

true

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7
Q

which dissociates faster: GDP tubulin or GTP tubulin

A

GDP tubulin

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8
Q

what does the exposure of GDP at the end of a microtubule result in

A

rapid depolymerization

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9
Q

what is catastrophe the result of

A

a growing microtubule losing its GTP cap

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10
Q

what does rescue require

A

GTP tubules to re-cap the end of a shortening microtubule

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11
Q

does the GTP cap hold the protofilaments straight or curved

A

straight

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12
Q

do GDP tubules favor curve or straight conformation

A

curved

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13
Q

what triggers hydrolysis of GTP

A

incoming heterodimers stimulate hydrolysis to previously added heterodimer

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14
Q

size of GTP-tubulin cap

A

unknown, but could be single layer

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15
Q

nucleation

A

forming base from which microtubules eminate

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16
Q

are heterodimers first attached on the - or + end

A

-

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17
Q

MTOCs (microtubule organizing centers)

A

almost always used by cells to nucleate microtubules

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18
Q

are MTOCs associated with the minus or plus end of microtubules

A

minus

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19
Q

most common animal cell MTOC

A

centrosome

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20
Q

centrosome composition

A

pair of centrioles at right angles to each other and some pericentriolar material

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21
Q

centriole composition

A

9 sets of triplet microtubules arranged in a circle to form walls of barrel-like structure

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22
Q

what are the centriole triplet microtubules made from

A

a and B tubulin, and S- and E- tubulin

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23
Q

pericentriolar matrix

A

composed of about 100 different proteins, including y-tubulin as part of yTuRC

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24
Q

yTuRC (y-tubulin ring complex)

A

the MTOC that does the actual nucleation of the microtubules

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25
structure of yTuRC
arranged as one turn of a very shallow helix, shape of lock washer - resembles one turn of helix made from microtubule protofilaments as they form the hollow tube in a spiral fashion
26
about how many spindle fibers per sister chromatid
40-50
27
where does the yTuRC nucleate microtubules from
their minus end
28
if the MTOC is near the nucleus, where will the plus ends bw
toward cell periphery
29
when does the centrosome get larger
interphase
30
when does each centriole duplicate
S phase (at right angles toward themselves)
31
additional MTOC in motile animal cells
basal bodies
32
basal bodies
serve as templates for assembly of axoneme
33
axoneme
bundle of microtubules that will form core of cilia and flagella
34
basal body structure
nine triplet microtubules
35
difference between basal body and yTuRC/centrioles
basal body: nucleates axonemal microtubules yTuRC/centrioles: nucleate astral ray microtubules
36
how do fungi nucleate and organize microtubules
spindle pole body embedded in nuclear envelope
37
how do plant cells nucleate and organize microtubules
nucleating sites distributed throughout cell cortex
38
how do epithelial cells nucleate and organize microtubules
nucleation sites near apical end of cell
39
what do various MTOCs all contain
y-tubulin - use similar mechanism to nucleate microtubules
40
at what phase do centrosomes reach the poles of cells?
prophase
41
how can microtubule dynamics be visualized
fluorescent tubulin: - expressing tubulin fused to fluorescent protein - injected cells with purified tubulin tagged with fluorescent dye
42
what is FRAP used to obtain
images of microtubule turnover
43
do interphase or mitotic microtubules have a longer half-time/rate of turnover
interphase
44
how does dynamic instability differ between in vivo and in vitro
1. plus ends grow faster in vivo 2. switch between growth and shortening more frequently in vivo 3. pauses common in vivo
45
where are dynamic instability switches more frequent
toward edges of cell near plasma membrane
46
do all cells have dynamic microtubule populations?
no, some cells have more stable populations
47
modifications of more stable microtubules
- capped at plus ends - contain more modified tubulin
48
where are stable microtubules more abundant
nonmitotic, differentiated cells
49
how do free microtubules exist
- broken off from anchored microtubules - have been released from centrosome
50
where can free microtubules be stabilized
at minus end
51
treadmilling
dynamic instability of microtubule plus end is biased toward net growth while the minus end shortens
52
why do cells have dynamic microtubules
need to adapt to new situations or new stages of CDC
53
ex. of how microtubules search interior of cell
during prophase they need to find and connect their plus ends to kinetochores
54
what happens to microtubules that don't hit a kinetochore
rapidly fall apart
55
what happens to microtubules that hit kinetochore
stabilized
56
where can dynamic microtubules detect a signal
plasma membrane - can induce polarization and begin to change shape
57
how are some proteins and organelles transported
have ability to hold on to tip of growing or shrinking microtubule
58
how is most movement in cells generated
molecular motors
59
do proteins usually bind to plus or minus end
more plus
60
MAPs (microtubule associated proteins)
family of proteins that bind to microtubules and: - speed/slow growth/shortening - function as linkers between the microtubule tip/sides and membrane vesicles or other structures
61
+TIPs
MAPs that bind to microtubules only at plus ends
62
how long are +TIPS bound
short time - continually falling off and being added
63
ex. of +TIP
CLIP-170
64
CLIP-170
stabilizes microtubules and promotes rescue by linking endosomes to microtubules
65
how to some MAPs make microtubules less stable
1. disrupt GTP cap 2. cut microtubules into pieces to make more ends to shorten 3. bind free tubulin subunits
66
katanin
cuts microtubules by binding to their walls and disrupting contacts between tubulin subunits
67
what energy does katanin uses
ATP
68
MCAK (mitotic centromere associated kinesin)
molecular motor that disrupts GTP cap by binding at microtubule ends and destabilizing the tip structure by favoring formation of protofilaments that curve away from microtubule wall
69
is MCAK recycled?
yes
70
what is MAP activity often regulated by
phosphorylation and dephosphorylation
71
molecular motors
microtubule-binding proteins that use repeated cycles of ATP hydrolysis to power continuous movement along the side of a microtubule
72
2 families of molecular motors
1. kinesins 2. dyneins
73
kinesins
usually move toward plus ends of microtubules
74
dyneins
only move toward microtubules' minus ends
75
for typical fibroblast cell, where do dyneins and kinesis usually transport:
dynein: toward center of cell kinesin: toward plasma membrane
76
what contributes to direction of movement and navigation by the motor?
polarity of polymer
77
why have no motors been identified on intermediate filaments
because it doesn't have polarity
78
two main methods of motor protein function
- motor proteins walk along anchored microtubule - motor proteins are anchored and move microtubule
79
characteristic shape of molecular motors
pair of large identical globular domains at end of long rod-shaped domain - sometimes second pair of smaller globular domains at other end
80
what binding sites are on the large globular domain (head/motor domain)
polymer and ATP
81
what are footsteps always taken by
heads
82
what does the tail domain bind to
cargoes
83
composition of molecular motors
several polypeptides, bulk is homodimer held together by coiled-coil interactions along rod-shaped region
84
stathmin
MAP that binds to free tubulin
85
kinesin with N-terminal motor domain
move vesicles toward plus end
86
kinesin with C-terminal motor domain
move vesicles toward minus end
87
kinesin with middle motor domain
regulated dynamics by using ATP hydrolysis to weaken microtubule cap
88
what is kinesin with middle motor domain similar to
MCAK
89
kinesin with bipolar motor domain
allows binding to 2 microtubules to slide them past each other - mitosis and cytoskeletal rearrangement
90
cytoplasmic dynein
homodimer with 2 motor domains
91
axonemal dyneins
cilia/flagella - heterodimers or heterotrimers, 2-3 motor domains per molecule

cell and molecular (21 decks)

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