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Cell Bio > Cytoskeleton > Flashcards

Cytoskeleton Flashcards

1
Q

what is the cytoskeleton

A

an intricate network of protein filaments that extend throughout the cell

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2
Q

what are the different cytoskeleton filaments

A
  • intermediate filaments
  • microtubules
  • actin filaments
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3
Q

what is the role of the intermediate filaments

A

enables cells to withstand mechanical stress

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4
Q

where are intermediate filaments found

A
  • throughout the cytoplasm
  • within the nucleus
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5
Q

what is the toughest and most durable of the cytoskeletal filaments

A

intermediate filaments

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6
Q

describe the structure of intermediate filaments

A
  • rope-like structure with many strands twisted together
  • two alpha helical monomers are wrapped together to form a coiled-coil dimer
  • two coiled-coil dimers run in opposite directions to form a tetramer
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7
Q

what holds intermediate filaments together

A
  • noncovalent bonding between subunits
  • combined strength of overlapping interactions provides tensile integrity
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8
Q

what allows for interactions between other components in the cell and intermediate filaments

A
  • central rod domains are similar in size and AA sequence
  • variance in the terminal ends allows interactions
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9
Q

what are keratin filaments and where are they found

A
  • cytoplasmic intermediate filaments
  • found in epithelial cells
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10
Q

what are vimentin and where are they found

A
  • cytoplasmic intermediate filaments
  • found in connective tissue, muscle, glial cells
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11
Q

what are neurofilaments and where are they found

A
  • cytoplasmic intermediate filaments
  • found in nerve cells
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12
Q

what are nuclear lamins and where are they found

A
  • nuclear intermediate filaments
  • found in all animal cells
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13
Q

what are nuclear lamina

A

intermediate filaments that form a 2D meshwork on the inner surface of the nucleus

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14
Q

how are nuclear lamina formed

A

phosphorylated (and dephosphorylation) of lamins allow for the disassembly and reassembly during cell division

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15
Q

how are intermediate filaments stabilized

A
  • by accessory proteins
  • allows for cross-linkage and connect them to other cytosolic cell components
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16
Q

what do accessory proteins do

A
  • interact w complexes that link the cytoplasmic cytoskeleton to structures in the nucleus
  • aids w organization and positioning of the nucleus
  • stabilize intermediate filaments
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17
Q

what do microtubules do

A
  • crucial role in organization in eukaryotic cells
  • system of tracks along which vesicles, organelles and macromolecules can be transported
  • can be rapidly dis/reassembled depending on needs
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18
Q

describe the structure of microtubules

A
  • comprised of tubulin molecules (dimer of alpha and beta tubulin)
  • dimers stack to form a hollow cylindrical microtubule of 13 parallel protofilaments
  • have structural polarity
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19
Q

describe the structural polarity of microtubules

A
  • plus end (beta)
  • minus end (alpha
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20
Q

where are microtubules formed

A
  • begins at specialized organization centers
  • the most prominent is the centrosome (located near the nucleus in non-dividing cells)
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21
Q

describe centrosomes

A
  • made up of 2 centrioles surrounded by a gel-like matrix of proteins containing gamma-tubulin rings (which are the starting points/ nucleations sites for microtubules)
  • negative ends of the microtubules are embedded in the centrosome
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22
Q

what controls the location, number, and orientation of microtubule

A

microtubule organization centers

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23
Q

what do all methods of microtubule organization use

A
  • gamma-tubulin rings to initiate growth
  • manage microtubule formation through the [ ] of free alpha/beta dimers
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24
Q

how do microtubules grow and shrink

A

through dynamic instability

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25
Q

what does dynamic instability allow for in microtubules

A

rapid remodeling and organization of microtubules

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26
Q

the action of dynamic instability is possible how

A
  • through GTP hydrolysis by tubulin dimers
  • each free tubulin dimer contains 1 GTP bound to beta-tubulin
  • GTP is hydrolyzed shortly after dimer is incorporated into a growing microtubule
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27
Q

what happens when tubulin dimers are added before hydrolysis can take place

A
  • accumulation of GTP-associated dimers
  • forms GTP-cap
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28
Q

how does the GTP cap form

A

accumulation of GTP-associated dimers

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29
Q

what is special about GTP-bound tubulin

A
  • form stronger bonds with neighbouring dimers
  • pack together more efficiently and promote growth
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30
Q

what happens when hydrolysis takes place before new tubulin dimers are added

A
  • loss of GTP-cap
  • weaker bonds between GDP-associated dimers favours disassembly
  • GDP-associated tubulin molecules rejoin cytosolic pool where they can exchange GDP for GTP and used for future polymerization
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31
Q

can cells modify dynamic instability of microtubules to suit their needs

A

yes

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32
Q

microtubules can direct traffic along their length _______(faster/slower) than the rate of free diffusion

A

much faster

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33
Q

movement along microtubules and other filaments is guided by what

A

motor proteins

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34
Q

what are motor proteins

A
  • dimers
  • have 2 ATP-binding heads, which facilitate movement through ATPase activity
  • have a single tail that bids to their cargo
35
Q

how do motor proteins move

A
  • the walking thing
  • the back leg gets ATP and conformational change and moves forward and then reattaches and repeat? idek but just remember conformation changes
36
Q

what are the two motor protein families

A
  • kinesins travel to plus end
  • dyneins travel to minus end
37
Q

what do kinesins do

A
  • motor proteins that move to plus end
  • diff kinds transport diff kinds of cargo
  • sometimes a single one can transport multiple
38
Q

what do dyneins do

A
  • motor proteins that move to minus end
  • always use adaptor proteins to interact w cargo
39
Q

what are responsible for positioning organelles

A

microtubules

40
Q

what are the roles of kinesins and dyneins as a cell grows

A
  • kinesins distribute the ER
  • dyneins keep golgi inwards towards the nucleus
41
Q

what are cilia

A
  • hairlike structures extending from the cell surface
  • contain a core of microtubules that can beat to move fluid or propel cells
42
Q

what are flagella

A
  • used primarily for locomotion
  • enable movement by propogating regular waves along their length
43
Q

what is the similarity of cilia and flagella

A

share a similar core structure

44
Q

describe the core structure of cilia and flagella

A
  • ring of 9 doublet microtubules around a pair of single microtubules in a 9+2 array
  • specialized form of dynein attaches one microtubule to another in each outer doublet
  • cross-linkage through accessory proteins holds the bundle together, leading to microtubule bending
45
Q

describe the structure of actin filaments

A
  • made up of a twisted chain of actin monomers
  • each monomer points in the same direction, making distinct polarity
  • filaments are thinner, shorter, and more flexible than microtubules, however there are more of them
46
Q

what are actin filaments used for

A

maintaining shape and movement

47
Q

how are actin filaments formed

A

actin monomers carry ATP which is hydrolyzed after it is incorporated into the filaments

48
Q

is polymerization quicker on the minus or plus end of actin filaments

A

plus

49
Q

what happens when the [ ] of actin monomers is high

A

filament can grow

50
Q

what happens when the [ ] of actin monomers is intermediate

A
  • treadmilling occurs
  • the rate of growth at the + end is matched by the rate of dissociated at the - end
  • this allows the filament to move forward in space
51
Q

how is polymerization of actin monomers regulated

A

protein binding

52
Q

what happens when actin filaments are needed

A

proteins like formins and actin-related proteins (ARPs) promote polymerization

53
Q

what happens when actin filaments are not in demand

A

proteins like thymosin bind to monomers to prevent polymerization

54
Q

what are myosins

A
  • belong to a family of motor proteins
  • bind and hydrolyze ATP to provide energy for movement along an actin filament
55
Q

what are the common myosin subfamilies

A
  • myosin I
  • myosin II
56
Q

describe myosin I

A
  • has a head domain that interacts w actin filament
  • has a tail that determines what type of cargo it can transport
57
Q

describe myosin II

A

has 2 heads that interact w the actin filament to form contractile bundles driving changes in shape, movement, and division

58
Q

where is actin found

A
  • throughout the cytoplasm
  • high [ ] just beneath the plasma membrane in the cell cortex
59
Q

what drives changes in cell shape and movement

A

rearrangement of actin filaments and associated myosin motors

60
Q

describe the steps of cell crwaling

A
  • actin polymerization the extension of exploratory motile structures at the leading edge
  • attachment transmembrane integrins adhere to molecules in the extracellular matrix and actin filaments in the cortex
  • contraction myosin motor proteins slide along actin filaments to drag the cell body forwward
61
Q

what are 2 examples of exploratory motile structures

A
  • lamellipodia
  • filopodia
62
Q

what is lamellipodia

A
  • the “sheet feet” that extend out at the front of the cells when they crawl
  • contain a dense meshwork of actin filaments
63
Q

how do filipodia add new monomers

A

formin binds to the growing + end of actin filaments

64
Q

how do lamellipodia add to the cell

A

ARPs form complexes that bind to the side of existing filaments and nucleate the formation of new filaments which grow out at an angle

65
Q

what controls the location, organization, and behaviour of actin filaments

A

actin-binding proteins

66
Q

what are actin binding proteins controlled by

A
  • extracellular signaling molecules
  • which activate intracellular pathways including monomeric GTPases from the Rho family
67
Q

what does Rho focus on

A

bundle assembly

68
Q

what does Rac focus on

A

lamellipodium formation

69
Q

what does Cdc2 focus on

A

filopodia formation

70
Q

what are the monometic GTPases in from the Rho family

A
  • Rho
  • Rac
  • Cdc42
71
Q

myosin involved in muscle contraction belongs to which myosin subfamily

A

myosin II

72
Q

describe the structure of skeletal muscle fibers

A
  • large, multinucleated cells formed by the fusion of many smaller cells
  • bulk of the cytoplasm is made up of myofibrils
  • each myofibril is made up of sarcomeres
73
Q

what are myofibrils

A

cylindrical contractile structures

74
Q

what are sarcomeres

A
  • contractile units
  • organized assemblies of actin and myosin filaments
  • actin + end anchors to Z discs
  • actin - end overlaps the myosin filaments
75
Q

how does muscle cell contraction happen

A
  • shortening of the cell sarcomeres
  • actin filaments slide along the myosin filaments w no change in length
76
Q

what are the steps of myosin walking for muscle contraction

A
  • attached at the rigor conformation as the myosin head lacks ADP or ATP
  • released ATP binds to the myosin head reducing its affinity for actin
  • cocked myosin head wraps around the ATP to facilitate hydrolysis, displacing the myosin head forward
  • rebinding and power stroke binding of the myosin head to a new site on the actin filament releases the phosphate group and allows myosin to return to its initial conformation and release ADP
77
Q

when does muscle contraction occur

A

when a skeletal muscle receives a signal from a motor neuron

78
Q

how is the signal from a motor neuron sent to a skeletal muscle

A
  • relayed through transvers tubules (t-tubes), that extend inward from the plasma membrane around each myofibril
  • signal is relayed to the SR
79
Q

what is the SR

A
  • sarcoplasmic reticulum
  • sheath of interconnected flattened vesicles that surround each myofibril
80
Q

what happens when the SR receives a signal

A
  • SR has high [ ] of Ca2+, which is released into the cytosol through specialized ion channels upon receiving a signal
  • the influx of Ca2+ activates calcium-sensitive molecular switches that are closely associated w actin filaments
81
Q

what does tropomyosin do

A

binds in the actin helix to prevent myosin heads from associating w actin filaments

82
Q

what does troponin complex do

A

undergoes conformational changes in response to Ca2+ which shifts tropomyosin molecules, allowing myosin heads to interact w actin filaments

83
Q
A

Cell Bio (11 decks)

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