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BIO130 > 2.4: The Cytoskeleton > Flashcards

2.4: The Cytoskeleton Flashcards

1
Q

list the 4 major functions of the cytoskeleton

A
  1. structural support: cell shape
  2. internal organization of cell: organelles, vesicle transport
  3. cell division: chromosome segregation, divide cell into two
  4. large scale movements: crawling cell, muscle contraction
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1
Q

list the 3 protein filaments that make up the network of the cytoskeleton

A
  1. actin
  2. microtubules
  3. intermediate filaments
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2
Q

which of the protein filaments present in the cytoskeleton contribute to the structural support

A

af, mt, if

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3
Q

which of the protein filaments present in the cytoskeleton contribute to the internal organization of the cell

A

mt

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4
Q

which of the protein filaments present in the cytoskeleton contribute to cell division

A

af, mt

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5
Q

which of the protein filaments present in the cytoskeleton contribute to large scale movements

A

af

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6
Q

compare and contrast the microscopy techniques to look at the cytoskeleton (light microscope, fluorescence microscope, transmission electron microscope)

A

light microscope
- resolution limit of ~200 nm
- limits from wv of visible light
- cannot resolve cytoskeletal filaments

fluorescence microscope
- reso limit of ~200 nm
- fluorescent labels are added to detect specific proteins eg immunofluorescence
- also makes it seem larger than it is

transmission electron microscope (best, better size accuracy)
- uses beams of e, very short wv
- reso limit of ~1 nm
- reveals detailed structures

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7
Q

state the diameter range of the cytoskeletal filaments

A

7nm to 25nm

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8
Q

describe the use of immunofluorescence microscopy in in cytoskeletal imaging

A
  • used to determine location of proteins within cell
  • cells are fixed (not live imaging) eg by using formaldehyde
  • primary antibody used to bind to specific protein of interest
  • secondary antibody binds to the primary antibody – covalently tagged to a fluorescent marker
  • fluorescence microscope used to excite fluorescent marker and visualize light emitted
  • Less amplification effect if you add fluorescence to the primary antibody compared to the second and also it’s more expensive (secondary is cheaper to buy)
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9
Q

order the filaments from smallest to largest

A

actin < intermediate < microtubules

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10
Q

through what interactions are cytoskeletal filaments held together by

A

filaments are held together by noncovalent interactions

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11
Q

what are actin filaments, intermediate filaments, and microtubules composed of

A

actin filaments - actin
intermediate filaments - intermediate filament proteins
microtubules - tubulin

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12
Q

name the two types of IF proteins and their purposes

A
  1. cytoplasmic IF: in animal cells subjected to mechanical stress (eg keratin filaments in epithelial cells of the skin), provide mechanical strength (overall examples include presence in connective-tissue cells, muscle cells, glial cells, nerve cells)
  2. nuclear IF: nuclear lamina (2d meshwork) formed by lamins in all animal cells that have a nucleus (plants have diff ones)
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13
Q

cytoplasmic IF proteins have a conserved _________________ central rod domain and they pack together into rope like filaments

A

a helical

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14
Q

t/f the N- and C- terminal domains differ in cytoplasmic IF proteins

A

true

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15
Q

t/f do cytoplasmic intermediate filaments have polarity, and why

A

no polarity bc no polarity in the tetramers bc the ends are the same

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16
Q

in cytoplasmic intermediate filaments:
2 monomers –> __________________
2 dimers –> _________________
__ (#) tetramers associate side by side and assemble into a _____________

A

2 monomers –> coiled coil dimer
2 dimers –> staggered antiparallel tetramer
8 tetramers associate side by side and assemble into a filament

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17
Q

in cytoplasmic intermediate filaments:
a) _______ region of monomer
b) _________ _____ dimer
c) ___________ __________ tetramer of b)

A

a helical, coiled coil, staggered antiparallel tetramer

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18
Q

describe the cytoplasmic intermediate filaments (what adjectives help it not rupture)

A

tough, flexible, high tensile strength

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19
Q

describe the role of intermediate filaments in an epithelial cell

A
  • keratin filaments in epithelial cells
  • form network throughout cytoplasm out to cell periphery
  • anchored in each cell at: cell-cell junctions (desmosomes), connect to neighbouring cells
  • provides mechanical strength
  • epithelium is the sheet of cells covering an external surface or lining an internal body cavity
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20
Q

what are microtubules involved in

A
  • cell organization: vesicle transport, organelle transport and positioning, centrosomes (animal cells)
  • mitosis
  • structural support: cells, motile structures (flagella, cilia)
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21
Q

name and describe the properties of tubulin

A
  • long, stiff hollow tubes (like cylinders)
  • inextensible (= not elastic)
  • made of individual subunits of a (-) and b (+) tubulin (closely related globular proteins) = tubulin heterodimer
    NOTE THAT THE + - IS NOT BC OF CHARGE
  • tubulin heterodimer is bound to GTP
  • arrangement of a and b subunits = polarity
  • 13 protofilaments (a line of heterodimers) = hollow tube
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22
Q

arrange the following into order of organization from smallest to largest (and how many of each if that is known)
protofilament, tubulin dimer, microtubule, tubulin

A

tubulin, tubulin dimer, protofilament, microtubule

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23
Q

the noncovalent bonds _________ protofilaments are weaker than the bonds ________ each protofilament (options: between, within)

A

between, within

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24
Q

t/f can growth and disassembly of microtubules occur at both ends

A

yes

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25
Q

which end of the microtubule is growth more rapid at

A

plus end

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26
Q

what happens after the protofilament has been there for awhile

A

After it’s been in a protofilament for a while, beta tubulin will cut GTP to GDP (a phosphate leaves) - and will change it from a t form heterodimer to a d form heterodimer - if we have t form dimers, we are more likely to have microtubule growth and then opposite for d form (shrinking) — any growing or shrinking can only occur at the ends

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27
Q

__ microtubule = __ parallel proton filaments forming the hollow tube. – some cells have bundles of microtubules (bundles of cylinders)

A

1, 13

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28
Q

in the cell, microtubules grow out from ___________

A

mtocs (microtubule, organizing centers)

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29
Q

which end of the microtubule is stabilized at mtoc

A

minus end (alpha end)

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30
Q

describe the growth process of dynamic instability in microtubules

A
  • free ab tubulin dimers bound to GTP are added to growing microtubule at + (beta end)
  • shortly after dimer is added to microtubule, b tubulin hydrolyzes gtp to gdp
  • rapid addition of ab tubulin dimers: faster than gtp hydrolysis in newly added ab tubulin dimers - leads to formation of gtp cap, stabilizes +
  • microtubule continues to grow
31
Q

what process is the dynamic instability of microtubules necessary for

A

remodelling

32
Q

how do the gtp cap on microtubules facilitate growth

A

Facilitates growth - it’s essentially the t form heterodimers (GTP bound) at the end

33
Q

which subunit of tubulin hydrolyze gtp into gdp

A

beta tubulin

34
Q

how can you identify the new tubulin dimers from old ones

A

gdp is old, gtp is new

35
Q

describe the shrinking process in the dynamic instability of microtubules

A
  • free ab tubulin dimers bound to GTP are added to growing microtubule at + (beta end)
  • shortly after dimer is added to microtubule, b tubulin hydrolyzes gtp to gdp
  • slower addition of ab-tubulin dimers - slower than gtp hydrolysis in newly added ab-tubulin dimers = loss of gtp cap, now gdp tubulin at + end has weaker binding = microtubule disassembles
36
Q

describe the full dynamic instability mechanism of microtubules

A
  • ab tubulin dimers: addition or loss at +
    • stabilized at mtoc
  • free ab tubulin dimers (gtp) added to growing microtubule
  • b tubulin gtp hydrolyzed to gdp = gdp tubulin dimer
  • tightly bound gtp to a tubulin is not hydrolyzed
  • gtp cap: straight filaments = stronger bonding, favors growth
  • gtp hydrolysis (gdp tubulin dimer): small conformational change = weaker binding, curved filaments = disassembly
37
Q

t/f tightly bound gtp to a tubulin is not hydrolyzed

A

true

38
Q

____ ____________ changes subunit conformation and weakens bond in the protofilaments

A

gtp hydrolysis

39
Q

what is the function of mtoc

A

have nucleating sites for microtubule growth - to start assembling new microtubules

40
Q

give an example of mtoc in animal cells

A

centrosome

41
Q

provide an example of a nucleation site (mtoc) and describe

A
  • y tubulin ring complex: protein complex of y tubulin & accessory proteins
  • ring of y tubulin (end) acts as an attachment site for ab tubulin dimers
    • end of microtubule at y tubulin ring complex
    • end of microtubule grows out
42
Q

differentiate between the use of dynamic instability needed for remodelling in nondividing and dividing animal cells

A

non dividing (interphase): most microtubules radiate from one centrosome (mtoc)
dividing: centrosome duplicates to form 2 spindle poles (mtocs), microtubules are reorganized to form a bipolar mitotic spindle - required microtubule dynamics

43
Q

in order for the cell to make the bipolar mitotic spindles, what does it have to do

A

The cell has to disassemble the first array to make the bipolar mitotic spindles

44
Q

microtubule associated proteins are able to: (at least 4)

A
  • nucleate growth of new microtubules
  • promote microtubule polymerization
  • promote microtubule disassembly
  • stabilize microtubules (prevent disassembly): protein bind to sides, plus end linking protein
  • branches
45
Q

give an example of how microtubules can be stabilized to prevent disassembly

A

cargo transport from the cell body to the axon terminal: how do nt synthesized in the er get to the axon terminals? through motor proteins on microtubules - er and golgi are located in the nerve cell body, these neurons can be a meter long (eg from spine to fingers)

46
Q

kinesin-1, cytoplasmic dynein are?

A

dimers

47
Q

what are the roles of the heads and tails of kinesin-1 and cytoplasmic dynein

A

heads move along microtubules, use atp hydrolysis for movement
tails transport cargo

48
Q

which directions do kinesin-1 and cytoplasmic dynein generally move in

A

kinesin-1 goes to + end (axon terminal)
cytoplasmic dynein goes to - end ((nerve) cell body)

49
Q

what is included in the cargo of kinesin-1 and cytoplasmic dynein

A

kinesin-1: cargo of organelles, vesicles, macromolecules
cytoplasmic dynein: worn-out mitochondria and endocytosed material

50
Q

gamma tubular ring complexes are located in the

A

centrosome

51
Q

describe the positioning of organelles by microtubules for er and golgi (+ what dimers are they composed of): eg for microtubules it foes from centrosome (mtoc) to cell periphery

A

er from nuclear envelope to cell periphery (by kinesin-1 to microtubule + (b)
golgi near centrosome by cytoplasmic dynein (towards microtubule - (a))

52
Q

t/f are actin filaments present in all eukaryotes

A

true

53
Q

actin filaments (aka microfilaments) are made of _________ <– describe it

A

actin monomers <– flexible, inextensible (can’t stretch)

54
Q

what are the motor proteins called (actin)

A

myosins

55
Q

list the 4 functions of actin filaments

A
  1. stiff, stable structures (microvilli)
  2. contractile activity
  3. cell motility (crawling)
  4. cytokinesis (contractile ring)
56
Q

describe the structure of actin filaments

A
  • helical filament
  • composed of a single type of globular protein: actin monomers - with non covalent interactions
    0 two protofilaments twisted in a right handed helix
57
Q

are actin filaments left or right handed helix

A

right handed helix

58
Q

do actin filaments have polarity

A

yes

59
Q

in which end of actin filaments is growth faster

A

the + end

60
Q

actin monomers are all in _________ orientation in each protofilament

A

the same

61
Q

describe the growth of actin monomers

A
  • free monomers are bound to atp - bound in the center of the protein
  • shortly after actin monomer added to filament: actin hydrolyzes atp to adp = reduces strength of binding between monomers in filament = more likely to dissociate if in adp form in one of the ends
  • rapid addition of actin monomers: faster than atp hydrolysis in newly added actin monomers
  • actin filaments have an atp cap that promotes growth
62
Q

to the following properties, identify whether intermediate filaments, microtubules, and/or actin filaments are able to conduct it:
- nucleotide bonding
- overall polarity
- motor proteins
- dynamic properties
- extensibility
- flexibility

A
  • nucleotide bonding: IF no, microtubules have gtp, actin has atp
  • overall polarity: IF no, others yes
  • motor proteins: IF no, others yes both atp
  • dynamic properties: IF is more stable, microtubules have dynamic instability, actin filaments conduct treadmilling
  • extensibility: IF yes, others no
  • flexibility: IF and actin flexible, microtubules stiff
63
Q

myosin I and II (actin motor proteins) are + or - end directed

A

+

64
Q

cytoplasmic dynein and kinesin-1 (microtubule motor proteins) are + or - end directed

A

cytoplasmic dynein -
kinesin-1 +

65
Q

atp hydrolysis is a ___________ change to generate ______

A

atp hydrolysis is a conformational change to generate force

66
Q

myosins generally move towards + or - end of actin filaments

A

+

67
Q

do myosin heads or tails move along actin filaments, and use atp hydrolysis for movement

A

heads

68
Q

differentiate between myosin I and II in terms of organization, tail domain, and role

A

myosin I: tail domain binds to cargo, used in vesicles (regulated secretion) and plasma membrane (shape)
myosin II: dimer assembles into myosin II filaments (through –>), tails organized in a coiled coil, eg is bipolar myosin II filament: slide actin filaments in opposite directions (+ end of both actin filaments) = generates contractile force
^^Looks like a double headed arrow – heads on the left and right are bound to different actin filaments and move towards each other (blue arrows) – the bipolar myosin moves them tgt and makes the contractile force

69
Q

bipolar myosin II filament: slide actin filaments in opposite directions (+ or - end of both actin filaments) = generates contractile force

A

+

70
Q

name some of the functions that are regulated by actin binding proteins

A
  • sequester actin monomers (prevent polymerization)
  • promote nucleation to form filaments
  • stabilize actin filaments (capping)
  • organize: bundle, cross-link filaments
  • severe actin filaments
71
Q

what is the name of the region for actin filaments and microtubules where there is disassembly

A

for actin: adp actin
microtubules: gdp ab tubulin dimer

72
Q

in order to push the leading edge/the cell forward, what must actin filaments rapidly do

A

rapidly assemble at the leading edge and disassemble further back

73
Q

explain cell crawling

A
  • dynamic changes in actin filaments
  • an example where actin filaments undergo treadmilling
74
Q

describe actin polymerization in a test tube (in vitro)
hint: there was a graph on the page if that helps job your memory

A
  • actin subunits (monomers) and atp added to a test tube (and some salt to solution to get process going)
    nucleation (lag phase): small oligomers form but unstable
    elongation (growth phase): some oligomers become more stable = leads to rapid filament elongation (faster at + end)
    steady state (equilibrium phase): decrease in actin subunits, rate of subunit addition = rate of subunit disassociation = treadmilling (there is always a % of free subunits in a steady state)
75
Q

why is growth of actin filaments slow at the beginning

A

Slow at the beginning bc needs to spontaneously make oligomers (not stable), once gets stable enough it’ll start to elongate

76
Q

what is the term for the process: loss of actin monomers at the - end (adp actin)

A

depolymerization

BIO130 (12 decks)

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