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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
Q

what is the GTP cap

A

when the MT is growing in vivo - the growing end of tubulin dimers that are still bound to GTP

26
Q

what happens to GTP tubulin dimers after they bind to a MT

A

intrinsic GTPase activity of the beta tubulin activates and leads to spontaneous hydrolysis of GTP

27
Q

when does the GTP cap grow

A

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
Q

why do the MT have “dynamic instability”

A

any given MT alternates between growing and shrinking -> constantly unstable

29
Q

what is the function of a microtubule

A

organizes the cellular components in eukaryotic cells and involved in forming the spindle fibers during cell division

30
Q

what are the 2 major classes of MT motor proteins

A

kinesins and dyneins

31
Q

what direction do the kinesins go

A

walk towards the plus end of the MT

32
Q

what is the function of a MT motor protein

A

move along the MT using energy of ATP hydrolysis, carrying some type of cargo with them

33
Q

what direction do dyneins go

A

towards the minus end of the MT

34
Q

what part of the motor protein hydrolyze ATP to induce movement

A

“feet” or globular heads (ATP binding sites)

35
Q

which MT motor protein is more complex and faster moving

A

the dynein

36
Q

what are the 2 major versions of dyneins

A
  1. cytoplasmic dyneins

2. ciliary dyneins (cilia and flagella)

37
Q

what does an increase in cAMP lead to

A

the activation of protein kinase A –> phosphorylation of both kinesin and dynein

38
Q

what happens with phosphorylation of kinesin

A

stimulates its activity and it walks towards the plus end (carrying the membrane bound pigment granule)

39
Q

what happens with phosphorylation of dynein

A

it inhibits its activity - stays bound to the membrane bound pigment granule but lets go of MT

40
Q

what happens to kinesin and dynein activity when cAMP concentration decreases

A

phosphates remove the phosphate group: kinesin is inactivated and dynein is activated - pigment granules move back towards the center

41
Q

what is the flagellar (and ciliary) structure

A

9 MT doublets (1 complete and 1 incomplete) and 2 singlets (single MT’s)

42
Q

what is the axoneme

A

the protein based structure without the cell membrane

43
Q

what type of dynein in in flagella and cilia

A

dynein arms “feet” (ciliary dyenins)

44
Q

what do cilia and flagella arise from

A

basal body (identical to centrioles of MTOC centrosome)

45
Q

what tubules continue from the basal body to form the doublets of the cilia/flagella

A

a complete A tubule and the 1st incomplete B tubule

46
Q

what direction are the ciliary dyneins

A

minus end directed MT motors

47
Q

where do the ciliary tubules walk when moving

A

along a neighboring tubule

48
Q

what happens when the tubules have linking proteins (nexin bridges and radial spokes)

A

the action of the dyenins causes the doublets (whole cilla/flagella) to bend

49
Q

what moves the duplicated centrosomes to the opposite poles of the cell division

A

centrosome associated motor proteins

50
Q

what does each new centrosome nucleate after moving to the two poles at the beginning of mitosis

A

nucleates a MT aster that radiates out from each pole

51
Q

what are the 3 categories of MT during cell division

A

kinteochores, polar and aster

52
Q

when do the polar MT’s form during prophase

A

when the plus ends of elongated spindle MT’s from opposite poles interact (forms bipolar interaction)

53
Q

what does the bipolar interactions do

A

stabilize the MT’s, preventing them from depolyermizing

54
Q

what happens to the MT’s during prometaphase

A

after the nuclear envelope breaks down, spindle MT’s (kinetochores) can now interact with the condensed chromosomes

55
Q

how are the 2 sister chromatids pulled apart during anaphase

A

a spindle MT from the opposite pole catches the kinetochore on the sister chromatid

56
Q

how are the chromosomes aligned at the metaphase plate

A

through the interaction of various MT motor proteins and the process of dynamic instability

57
Q

what happens during anaphase A

A

kinetochore MT shorten by depolymerization at the plus end

58
Q

what happens during anaphase B

A

overlapping polar MT elongate and slide past each other, pushing the poles and chromosomes further apart (both kinesis and dynein motor proteins)

59
Q

Is ATP involved during anaphase A and B

A

no it is independent of ATP

MCBM Part 1 (29 decks)

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