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Cell Molec > Lecture 19 > Flashcards

Lecture 19 Flashcards

1
Q

what are the subunits of microtubules?

A

heterodimer (a/b) tubulin

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2
Q

what is alpha(a)-tubulin

A

the (-) end where GTP is NEVER hydrolyzed, just there

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3
Q

what is beta(b)-tubulin

A

the (+) end where GTP can be hydrolyzed/exchanges

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4
Q

what is a microtubule protofilament

A

one “string”/strand of heterodimer tubulins

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5
Q

what is the direction of assembly of microtubules?

A

at the (+) end

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6
Q

singlet

A

13 MT protofilaments in a ring formation

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7
Q

doublet

A

13+10 MT protofilaments in a 2-ring formation

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8
Q

triplet

A

13+10+10 MT protofilaments in a 3-ring formation

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9
Q

difference between microtubule and microfilament assembly occurrence

A

microfilaments can be assembled anywhere, microtubules can only be assembled from a small number of locations in the cell

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10
Q

where are microtubules assembled?

A

only at MTOC

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11
Q

what is MTOC

A

microtubule organizing centers, such as the centrosome

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12
Q

which cell type is does not strongly require MTOCs

A

dendritic cells

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13
Q

what end of the microtubules stays at the MTOCs?

A

the (-) end stays, (+) end radiates

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14
Q

what are centrosomes

A

made up of 2 centrioles at right angles of each other (mom and daughter centrioles)

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15
Q

what are centrioles composed of?

A

triplet MT protofilament rings

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16
Q

what triggers catastrophe?

A

when GTP hydrolysis rate is higher than assembly rate

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17
Q

what triggers rescue?

A

when GTP hydrolysis rate decreases and there is an increase of GTP-bound to b-tubulin

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18
Q

how are MT protofilaments assembled?

A

when there is a high concentration of GTP-b-tubulin added to (+) end

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19
Q

what is catastrophe

A

when microtubules have a GDP-b-tubulin cap = cause it to curve and limp and undergo rapid disassembly

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20
Q

what is rescue

A

when microtubules have a GTP-b-cap = favors assembly by adding more GTP-b-tubulins

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21
Q

what are the motor proteins of microtubules?

A

kinesin and dynein

22
Q

what are kinesins?

A

microtubule motor proteins that move toward (+) end

23
Q

what are the three parts of kinesins?

A

tail, stalk, and 2 heads

24
Q

which part of the kinesin binds to the microtubule?

A

the heads

25
Q

which (ATP or GTP) binds to the heads of kinesins?

A

ATP

26
Q

function of kinesin-1

A

anterograde transport of vesicles

27
Q

how does kinesin bind to vesicles

A

the tail domain binds to the kinesin receptor on the vesicles

28
Q

function of kinesin-2

A

(heterotrimeric) transports organelles

29
Q

function of kinesin-5

A

(bipolar head ends, no tail) microtubule sliding in cell division

30
Q

function of kinesin-13

A

disassembly of microtubules from both ends

31
Q

what term is used to describe the movement of kinesins on microtubule tracks?

A

walking

32
Q

what is different about kinesin-1?

A

highly processive motor protein = will take so many “steps” before it will fall off

33
Q

what is dynein

A

MT motor protein that moves towards (–) end

34
Q

components of dynein

A

stem, 2 heads, stalk, MT-binding domain

35
Q

how do dyneins move along the MTs?

A

they jump

36
Q

what do dyneins use to be able to move along MTs?

A

ATP-hydrolysis

37
Q

function of dynein

A

transport of organelles towards (–) end, towards MTOCs

38
Q

how do dyneins attach to their cargo?

A

via dynactin, cannot interact with cargo directly

39
Q

what is dynactin

A

a coiled-coil adapter protein associated with dynein to bind to its cargo

40
Q

function of intermediate filaments

A

gives cells their strength and structure

41
Q

structure of intermediate filaments

A

different coiled-coil dimers that form a tetramer

42
Q

what is a protofilament of intermediate filaments?

A

a tetramer of the coiled-coil structures

43
Q

what is a protofibril of intermediate filaments?

A

4 intermediate filament protofilaments

44
Q

what makes up the final structure of intermediate filaments?

A

4 intermediate filament protofibrils

45
Q

why can’t intermediate filaments be used as tracks?

A

there is no polarity due to the symmetric ends

46
Q

where are intermediate filaments class I & II present?

A

epithelial cells

47
Q

where are intermediate filaments class III present?

A

smooth & skeletal muscles

48
Q

where are intermediate filaments class IV present?

A

neurons

49
Q

where are intermediate filaments class V present?

A

nucleus (lamins)

50
Q

what are lamins

A

intermediate filaments in the nucleus that provide its organization and rigidity

51
Q

functions of lamins in the nucleus

A

structure, positioning nucleus within the cell, lines inner membrane, associates with chromatin regulating gene expression, associates with LINC complexes

52
Q

what are LINC complexes?

A

proteins that cross nuclear envelope that interact with other cytoskeletal proteins

Cell Molec (16 decks)

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