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MCBM Part 1 > Talbot - Microtubules > Flashcards

Talbot - Microtubules Flashcards

1
Q

what are the 3 components of the cytoskeleton

A

intermediate filaments, microtubules, and actin filaments

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2
Q

what allows the site specific rapid growth of the cytoskeletal elements

A

disassembly of filaments and rapid diffusion of small subunits

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3
Q

what is the most common spot for removal or breakage of protofilaments

A

removal from one end (breaks one longitudinal and 2 lateral bonds instead of 4)

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4
Q

what creates stability of protofilaments

A

parallel interactions (side-to-side) non-covalent bonds

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5
Q

how many protofilaments make up a microtubule (MT)

A

13 protofilaments - alternating dimers of alpha and beta tubulin

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6
Q

what direction are the protofilaments oriented in

A

the dimers are always the same direction and the protofilaments are in the same direction

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7
Q

what are the two ends of the MT (microfilament) called

A

minus end and plus end (not referring to charge)

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8
Q

what is different about the minus and plus ends of a MT

A

they differ in their tendency to interact with other tubulin dimers

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9
Q

what situation does the plus end grow and the minus end where the dimers come off

A

in vitro

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10
Q

what happens in vivo to the minus and plus ends of the MT

A

the minus end is capped off (stabilized) so both growth/polymerization and shrinkage/depolymerization occurs at the plus end

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11
Q

what does the MT depend on for growing/ or shrinking

A

whether GTP or GDP is associated with the tublin dimers

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12
Q

what does GTP have a high affinity for

A

plus end of a mictotubule (more likely to interact/bind with the plus end)

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13
Q

what hydrolyzes GTP into GDP

A

beta tubulin

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14
Q

what does GDP have a low affinity for

A

other tubulin dimers (stuck in the middle of the MT)

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15
Q

how do GTP-tubulin dimers form MT’s in vitro (test tube)

A

with appropriate conditions they spontaneously interact and form MT’s

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16
Q

what is the initial phase called where individual dimers begin to associate

A

nucleation (lag phase)

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17
Q

is the initial rate of nucleation of MT’s fast or slow

A

growth is slow - MT protofilament is almost as likely to dissociate as it is to continue to grow

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18
Q

what is the steady state length or the equilibrium phase of MT polymerization

A

when the rate of addition on the plus end equals the rate of removal from the minus end (concentration of GTP-tubulin dimers has fallen)

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19
Q

what causes nucleation of MT’s in vivo

A

occurs due to the presence of a gamma tubulin nucleation ring (Microtubule Organizing Center MTCO)

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20
Q

how do the MT’s orient themselves and grow from the MTOC (microtubule organizing center)

A

MT grow out from the MTOC, minus ends are towards the center and plus ends are oriented towards the cell periphery (plasma membrane)

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21
Q

what is the MTOC called in animal cells

A

the centrosome

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22
Q

what are the 2 parts of the centrosome

A
  1. pair of centrioles

2. pericentriolar material- centrosome matrix

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23
Q

what are located in the pericentriolar material

A

electron dense cloud in which the gamma tubulin nucleation ring complexes (gamma TuRC) are found

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24
Q

what is the centriole composed of

A

“microtubule based structures” 9 triplet structures (each has 1 complete MT ring and 2 incomplete) - also have multiple accessory proteins associated with the centrioles

25
what is the GTP cap
when the MT is growing in vivo - the growing end of tubulin dimers that are still bound to GTP
26
what happens to GTP tubulin dimers after they bind to a MT
intrinsic GTPase activity of the beta tubulin activates and leads to spontaneous hydrolysis of GTP
27
when does the GTP cap grow
is the addition of GTP-tubulin dimers is faster than the rate at which GTP is hydrolized (if it is slower the GTP cap shrinks)
28
why do the MT have "dynamic instability"
any given MT alternates between growing and shrinking -> constantly unstable
29
what is the function of a microtubule
organizes the cellular components in eukaryotic cells and involved in forming the spindle fibers during cell division
30
what are the 2 major classes of MT motor proteins
kinesins and dyneins
31
what direction do the kinesins go
walk towards the plus end of the MT
32
what is the function of a MT motor protein
move along the MT using energy of ATP hydrolysis, carrying some type of cargo with them
33
what direction do dyneins go
towards the minus end of the MT
34
what part of the motor protein hydrolyze ATP to induce movement
"feet" or globular heads (ATP binding sites)
35
which MT motor protein is more complex and faster moving
the dynein
36
what are the 2 major versions of dyneins
1. cytoplasmic dyneins | 2. ciliary dyneins (cilia and flagella)
37
what does an increase in cAMP lead to
the activation of protein kinase A --> phosphorylation of both kinesin and dynein
38
what happens with phosphorylation of kinesin
stimulates its activity and it walks towards the plus end (carrying the membrane bound pigment granule)
39
what happens with phosphorylation of dynein
it inhibits its activity - stays bound to the membrane bound pigment granule but lets go of MT
40
what happens to kinesin and dynein activity when cAMP concentration decreases
phosphates remove the phosphate group: kinesin is inactivated and dynein is activated - pigment granules move back towards the center
41
what is the flagellar (and ciliary) structure
9 MT doublets (1 complete and 1 incomplete) and 2 singlets (single MT's)
42
what is the axoneme
the protein based structure without the cell membrane
43
what type of dynein in in flagella and cilia
dynein arms "feet" (ciliary dyenins)
44
what do cilia and flagella arise from
basal body (identical to centrioles of MTOC centrosome)
45
what tubules continue from the basal body to form the doublets of the cilia/flagella
a complete A tubule and the 1st incomplete B tubule
46
what direction are the ciliary dyneins
minus end directed MT motors
47
where do the ciliary tubules walk when moving
along a neighboring tubule
48
what happens when the tubules have linking proteins (nexin bridges and radial spokes)
the action of the dyenins causes the doublets (whole cilla/flagella) to bend
49
what moves the duplicated centrosomes to the opposite poles of the cell division
centrosome associated motor proteins
50
what does each new centrosome nucleate after moving to the two poles at the beginning of mitosis
nucleates a MT aster that radiates out from each pole
51
what are the 3 categories of MT during cell division
kinteochores, polar and aster
52
when do the polar MT's form during prophase
when the plus ends of elongated spindle MT's from opposite poles interact (forms bipolar interaction)
53
what does the bipolar interactions do
stabilize the MT's, preventing them from depolyermizing
54
what happens to the MT's during prometaphase
after the nuclear envelope breaks down, spindle MT's (kinetochores) can now interact with the condensed chromosomes
55
how are the 2 sister chromatids pulled apart during anaphase
a spindle MT from the opposite pole catches the kinetochore on the sister chromatid
56
how are the chromosomes aligned at the metaphase plate
through the interaction of various MT motor proteins and the process of dynamic instability
57
what happens during anaphase A
kinetochore MT shorten by depolymerization at the plus end
58
what happens during anaphase B
overlapping polar MT elongate and slide past each other, pushing the poles and chromosomes further apart (both kinesis and dynein motor proteins)
59
Is ATP involved during anaphase A and B
no it is independent of ATP

MCBM Part 1 (29 decks)

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