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BSCI330 SPRING > exam 3 cytoskeleton > Flashcards

exam 3 cytoskeleton Flashcards

1
Q

what is the cytoskeleton

A

a system of protein filaments that provide structure and mechanical support for the cell

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2
Q

what are the three main types of fibers in the cytoskeleton

A

microbtubules (polymers of tubulin), microfilaments (of actin), intermediate filaments (of helical proteins)

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3
Q

what are cytoskeletal filaments made up of

A

smaller repeating subunits that self-assemble into large fibers

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4
Q

what are actin and tubulin fibers polarized with

A

positive and negative ends, where polymerization and depolymerization occur asymmetrically

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5
Q

what do motor proteins allow for

A

allow cargo to be transported along cytoskeletal fibers and can also be used to generate large cellular shape changes

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6
Q

what is the size scale of cytoskeletal fibers

A

microtubules are biggest, intermediate filaments are medium size, microfilaments are smallest in diameter

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7
Q

what are cytoskeletal structures constructed by

A

the polymerization of monomeric protein subunits

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8
Q

what does disassembly and reassembly allow for

A

changes in cell shape and/or internal movements of organelles/vesicles

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9
Q

what does the polymerization of cytoskeletal monomers require

A

nucleoside triphosphate in the form of either GTP (tubulin) or ATP (actin) (together = NTP)

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10
Q

what cytoskeletal monomers have a higher affinity for their binding partners

A

containing NTP over NDP

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11
Q

what occurs at the plus end of the cytoskeleton

A

addition if NTP bound

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12
Q

what occurs at the minus end of the cytoskeleton

A

release if NDP bound

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13
Q

what is actin composed of

A

a network of flexible filaments dispersed throughout a cell - highly concentrated beneath the plasma membrane (called the “cortex”)

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14
Q

what does actin form

A

the basis of cell shape and structure and the contractile rings of dividing cells

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15
Q

what does actin do

A

aids in the contraction of muscle cells and propels vesicles and other cellular compartments through the cytoplasm

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16
Q

what are the actin monomers

A 
globular actin (G actin), which polymerizes into actin polymers (F actin)
- two strands of actin wind around each other to form intact microfilaments
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17
Q

where are actin monomers bound to ATP added

A

to the plus end of the growing filament (ADP monomers are lost from the minus end)

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18
Q

what is treadmilling

A

dynamic instability actin exhibits where addition at positive end is equal to removal at minus end

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19
Q

what are the ways tubulin/actin is changed

A

increase nucleation, depolymerization

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20
Q

what do the rho family of GTPases do

A

act as molecular switches to control actin polymerization dynamics by regulating the activity of actin-binding accessory proteins

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21
Q

what does Rho-GTP do

A

regulates actin binding and stress fibers

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22
Q

what does Rac-GTP do

A

regulates actin polymerization and can generate structures of lamellipodia and membrane ruffles

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23
Q

what does Cdc42-GTP do

A

regulates actin polymerization and bundling, filopodia, and microspikes

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24
Q

what do microtubules form

A
  • a network of rigid tubules that radiate through the cytoplasm of all eukaryote cells
  • mitotic spindles of dividing cells
  • the core of motile appendages: cilia and flagella
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25
Q

what are microtubules formed from

A

alpha and beta tubulin (both bind GTP, but only beta hydrolyzes GTP)

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26
Q

how does the plus end of microtubules grow

A

by the addition of tubulin dimers bound to GTP

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27
Q

where are tubulin dimers lost

A

from the minus end of microtubules, which grows slow and contains more GDP

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28
Q

when is alpha-beta tubulin bound to GDP/GTP

A

GDP at minus end, GTP at + end

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29
Q

how does the plus end maintain a GTP cap

A

rate of polymerization at plus end is more rapid than rate of GTP hydrolysis

30
Q

when is the GTP cap lost

A

when the rate of GTP hydrolysis exceeds the rate of polymerization

31
Q

what is catastrophe

A

when the plus end undergoes rapid depolymerization

32
Q

what is NFAT

A

a transcription factor for activating immune system players regulated by localization - part of calcium signaling pathway; regulated by phosphorylation/dephosphorylation

33
Q

how is actin asymmetric and directional

A

actin monomer assembles in directional way so one end points toward plus end and other points toward minus of microfilament - add on plus end, disaffiliate on minus end

34
Q

how is tubulin different from actin

A

minus end of tubulin is fixed and we don’t get loss of GDP bound monomers from minus end

35
Q

how is actin dynamic at both ends

A

add at plus end and subtract at minus end - size of filament is based on simultaneous rates of addition and subtraction

36
Q

what can the growth or shrinkage of microtubules be regulated by

A

altering the balance between the addition and removal of tubulin dimers

37
Q

how can you stabilize microtubules

A
  • binding subunits to prevent assembling into microtubules
  • enhancing GTP hydrolysis to enhance disassembly
  • severing microtubules
  • linking + ends to other structures
  • stabilizing + ends of tubules
  • binding along side tubules to stabilize them
38
Q

what are the two phases of microtubule assembly

A
  • nucleation: small portion of tubule formed at the beginning
  • elongation: addition of tubulins and the GTP-cap
39
Q

what are microtubule organizing centers (MTOC’s)

A

two barrel-shaped centrioles surrounded by centrosome matrix, which each contain nine fibrils, each composed of three microtubules

40
Q

what can be used to generate directional motion

A

protein shape changing

41
Q

how does movement become directional in order to be useful

A

couple shape change in one direction with ATP hydrolysis - makes an irreversible step when hydrolyzed

42
Q

in which direction is movement favorable

A

ATP -> ADP + Pi

43
Q

how is motion generated

A
  • the protein starts in one position
  • the binding to ATP causes a shape change where the protein takes a step forward
  • ATP is hydrolyzed, which makes for another step forward.
  • can release ADP and phosphate to bring protein back to original conformation, but it has taken a step forward at that point
44
Q

what are myosins

A

a huge family of motor proteins that bind to actin microfilaments

45
Q

what is the myosin II structure

A

heteromer with 6 polypeptide chains - one pair of heavy and two pairs of light chains

46
Q

what does each heavy chain of myosin II contain

A

a “S1” head with ATP-ase activity, a neck region, a coiled-coil tail

47
Q

what can myosin II molecules associate into

A

filaments, which form a basic structural unit of the contractile machinery

48
Q

how can myosin II move actin filaments

A

by attaching to actin filaments, moving with the release of ADP and then detaching when ATP binds - myosin moves from - to + end

49
Q

what are kinesins

A

microtubule-associated motor proteins

50
Q

what do kinesins do

A

motor protein responsible for moving vesicles and organelles along nerve axons from the cell body to the synaptic terminals

51
Q

what are kinesins composed of

A

two light and two heavy chains - heavy chains are entwined to create a stalk region made up of coiled alpha-helices

52
Q

what do the two heads of the heavy chains of kinesins have

A

ATP-binding sites and bind to microtubules initiating ATPase activity and the movement of the kinesin molecules and cargo along the microtubule

53
Q

what are the lagging and leading heads bound to in kinesins

A

lagging head is bound to ATP, leading is bound to ADP - hydrolysis allows for “walking” - moves - end to + end of microtubules

54
Q

what are dynesins

A

a family of microtubule based motor proteins

55
Q

how can kinesins interact with organelles

A

light chains in tail can interact with the cargo and the different types go to different locations in cell

56
Q

how can cargo be loaded on and walk along microtubule

A

adaptor proteins interact with kinesins to allow for this

57
Q

what is the structure of dynesins

A

dimer of heavy chains with two ATP-binding heads and a stalk (with intermediate and light chains)

58
Q

what is dynactin

A

a complex of proteins that light chains can bind to a cargo through

59
Q

how do dynesin molecules move along microtubule protofilaments

A

in a similar manner to kinesin, from the + end to the - end of the microtubule

60
Q

how can cells regulate which direction something is moving in

A

by whether it asociates with dynamin or kinesin

61
Q

what involves hydrolysis of ATP

A

depolymerization of actin filaments, movement of myosin along an actin fiber, movement of kinesin along a tubulin fiber

62
Q

what are intermediate filaments composed of

A

a group of related long helical proteins

63
Q

what do intermediate filaments do

A

provide mechanical strength to cells

64
Q

how are intermediate filaments formed

A

via coiled-coil interactions of alpha helical proteins

65
Q

what do lamins do***know!!

A

intermediate filament that provides structural support to nucleus

66
Q

what do keratins do***know!!

A

intermediate filament that provides strength to epithelial cells

67
Q

what are axons***know!!

A

intermediate filament that provides strength for long, extended neurons

68
Q

what are actin filament-/microtubule affecting drugs

A

drugs that bind cytoskeletal proteins and affect their assembly/disassembly dynamics

69
Q

what are the actin filament–affecting drugs

A
  • latrunculin - binds G-actin monomers and prevents assembly of filaments
  • phalloidin - binds F-actin filaments and prevents disassembly
  • cytochalasins - bind + ends and suppress filament dynamics
70
Q

what are the microtubule-affecting drugs

A
  • nocodazole - binds tubulin dimers and prevents microtubule assembly
  • taxol - binds to microtubules and stabilizes them to prevent disassembly/ inhibit cell division
  • colchicine - copolymerizes into the microtubule lattice, suppressing microtubule dynamics

BSCI330 SPRING (24 decks)

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