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CMCB Fall > Myosin > Flashcards

Myosin Flashcards

1
Q

Do microtubules havae fast/slow turnover?

A

Fast (except for stable nuerons)

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2
Q

Some functions of microtubules

A

…

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3
Q

What structures do all myosins have in common?

A
  1. Ne terminal head domains (bind to actin and exhibit ATPase activity)
  2. variable sized taild omain that dictates specific interactions of myosin with other proteins
  3. some type of associated light chain
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4
Q

What are “conventional myosin” and where are they formed?

A

Myosin II

Form thick filaments and involved n actin-myosin sliding contraction

In msucle but foudn in non-muscle cells as well

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5
Q

What are unconventional myosins? What are their funciton?

A

DO NOT FORM FILAMENTS

not involved iwth muscle conrcations
invovled in other cell movements

Transprot of membrane vesicles along filament, phagocytosis, extenion of cell processes

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6
Q

Is ATPase activity and actin binding function of myosin head domain conserved for various myosin isotypes>

A

YES!

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7
Q

What 2 funcitons fo myosin head domains are conserved in myosin head domains

A
  1. ATPase

2. Actin-binding function

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8
Q

What is myosin broken down to with treatment with proteoylytic enzmes?

A
  1. LMM - lght meromyosin

2. HMM- heavy meromyosin

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9
Q

What is LMM composed of

A

Light meromyosin

Tail myosin

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10
Q

What is HMM composed of?

A

Heavy meromyosin

S1 fragment + S2 FragmentHEAD Piece with ATPase activity and actin binding activity

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11
Q

What does HMM breakdown to with further Tx

A

S1 fragment- myosin heads + actin binding portion

  1. S2- rod like fragment
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12
Q

What are S1 fragments used for? What direction do arrowheads point?

A

To demonstrate polarity of actin filaments

Arrowheads piont to the (-) slow gorwing ends while barbed ends are at teh (+) ends for the microfilaments

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13
Q

What is a bare zone

A

Free of mysoin head dominates this area = all tails

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14
Q

Describe Myosin Polarity-

A

Bipolor!

Myosin molecules (~300) aggregate together by means of tial region- heads on the outside

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15
Q

Describe Myosin II filaments in non-muscle

A

Much smaller (15-20 molecules) but have similar bipolar arrangements

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16
Q

What are lenght of skeletal muscle cell? Width

A

Lenght- 2-3 cm long

Width- 100 nm wide

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17
Q

What ar the four classes of muscle cells in mammals

A

Heart muscle, Smooth muscle, Myoepithelial cell, Skeletal muscle fiber

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18
Q

Skeletal muscles

A

multinucleated cell

cells form via fusion of myoblasts; once fomred they are generally non-mitotic

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19
Q

Heart msucle

A

only have one nucleaus per cell

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20
Q

Smooth muscle

A

do not appear straited- foudn in regions like eigstiv tract or around arteries and veins

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21
Q

Myoepithelial cells- non stirated

A

ecotdermally dericed (unlike other muslce ells) serve to expel fluids (saliva, sweat, milke) from glandular tissue

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22
Q

Diameter or myofibril

A

1-2 um

myofibirls comprised of long repeated chains of tiny contracile units- called sarcomeres

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23
Q

What direction (minus or plus) end of actin near Z lines?

A

Plus ends are towards Z lines!

Minus ends are towards M lines

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24
Q

A bands are anisotropic

I bands are isotropic

A

yeeeppp

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25
Q

What is Titin?

A

associated with mysoin thick filaments

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26
Q

How far does titin extend? What are its characterisitcs?

A

Z–> M line

Elastic changes lenght as sarcomere contracts and rleaxes

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27
Q

What are nebulin?

A

Assocaited with actin fibers

same lenth as thin filmants

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28
Q

What is Cap Z

A

Anchors (+) end of actin to Z-line

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29
Q

What does Z-disc contain?

A

alpha actinin and IF (Desmin)

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30
Q

What is polarity of Myosin fibers?

A

Same relative poslarity-

Myosin heads have + ends and tails are -

M yosin heads oeprate with low processivity sot hey don’t hodl each other back

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31
Q

What percent of cycelt time is Myosin Head bound to Actin?

A

5% of cycle time

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32
Q

Does myosin walk towards (+) or (-) ends of actin

A

Positive end of actin, close to Z line

33
Q

What is the complex of the Troponin complex or 3 polypeptides

A
  1. T- tropoyosin binding
  2. I: Inhibitory
  3. Calcium-biding
34
Q

What happens with I-T complex undar increase in Clacium

A

calcium binds to Troponin C–> Troponin I rleases Actin

35
Q

what is tropomyosin?

A

elongated molecule that binds along groove of actin helix

36
Q

What is Hypertorphic Cardiomyopathy

A

Mutations in genes encoding contractile proteins

death in young atheletes

]Familial,

genes including myosin llight cahins, myosin heavy chains, cardiac troponin or tropomyosin

37
Q

In SM and non-muscle cells, Myosin II is activitated yb? Why? What enzyme is in charge of it?

A

Phophorylation–> in order to form filaments

MLCK (myoskin Light chain knase)

38
Q

What phosphorylates Mysoin II?

A

MLCK enzyme

39
Q

Wht happens when Myosin II in non-muscle is phosphorylated?

A

Releases Myosin Tail from Sticky Patch in Myosin Head –> Tails assemble into short, bipolar thick filaments

40
Q

Thickness of MII in non-msucle vs skeletal muscle

A

Thinner b/c 15-20 moleucls vs hudnreds

41
Q

In SM,

1) Actin: mysoin ration vs in sk musclte
2) ATPase activity

A

In SM , Act:Myosin ratio higher

ATPase activity lower in smooth muslce

42
Q

What attaches thin filaments (actin) to cell membrane in SM?

A

Dense bodies with alpha actinin

INtracellular scaffolding of IF- DESMIN

Thin is interdigiteded between thick filaments`

43
Q

What is the contractile ring made up of ( funciton sduring cytokineses)

A

Actin-Myosin II in non muscles that pinch daughter cells

end of mitosis during cytokineses

44
Q

What are two unconventional Myosin Examples? Function? How theyre differnt form Myosin II

A

Myosin I

Myosin V

Smaller tale domains

Assocated with structures such as membrane vesicles and organelles

45
Q

Myosin I

A

One headed motor head moves along atin

Tails carry cargo in microvilli

Myosin I is invovled in moving membrane vesicles along the central core of MF in teh microvilllus

46
Q

Myosin V

A

forms dimers and functions as 2-headed motor

Myosin V reads the polarity of actin filaments and tranpsorts cargo bound to its tal piece (IF) towards teh plus ends of actin filaments

TOWARDS PLUS END

47
Q

Waht is the fucntion of Intermediate Filaments?

A

Major structural elemetns that provide mechanism support and structure to cells

48
Q

Do they have fast/slow turnover?

A

SLOOWWWWW! long-lived (like hair, hails, insoluble)

49
Q

Involved in cell motiliy?

A

No

50
Q

Are there a lot or a little>

A

A lot

abundant in some cells far more than MTs or MF

51
Q

Soluble/Insoluble

A

Insoluble

52
Q

Diameter

A

10-11 nm

53
Q

What are four types of IF

A

Nuclear

Vimentin-like

Epithelial

Axonal

54
Q

Which ones of the IFs are OBLIGATORY HETERPOLYMERS

A

Epthelial

Axoanl

55
Q

What are the components polypeptides of nuclear IF

A

laminins A, B,C

found in nuclear lana (all nucleated cells)

56
Q

What are component polypeptides of vimentin-like

A
  1. Vimentin
    (manycells of mesenchymal orgiin, fibroblast, lymphosyte, endothelial cells)

2 .Desmin (ONLY in muscle)

3.Glila fibrilaly acidic protein
(glila cells (astrocytes an some Schwann cells)

  1. Peripherin- some neurons
57
Q

What are components of epithelial polypeptides

A

Type I Keratins (acidic)

Type II kertains (basic)

in epithelial cells and their derivatives

58
Q

What are components of Axonal Componetn polypeptides

A

Neurofilament proteins (NF-L- NF-M and NF-H_

59
Q

Are type I kertains acidic of basic?

A

Acidic (heteropolymer)

60
Q

Are tyep II kertains acidic or basic?

A

Basic (heteropolyemr

61
Q

what is conserved in all IFs

A

Conserved core domain

Central rod domain

DIfferent heads and tials

62
Q

Chaaracteristic of rod domain

A

Dimer coiled cords

Tetramers formed by anti parallel aggregation of 2 coil-coiled dimers –> rope

63
Q

What are protofilaments?

A

Tetramers taht aggregateend to end

Assocaite alterally, forming final IF that is 10-11 nm thick

64
Q

How any IF proteins molecules present

A

32 IF protein molecules

65
Q

Where are keratins located?

A

Intracellulary in epi cells layer of skin at specialized cell-cell jucntions called spot desmosomes

IFs are also foudn as HEMIDESMOSMES where epithelial cells make connections with ECM

also present EXTRACEULLARY as keratinziedlayer of skin as well as in specialized derivatives of epithelal cells hair and nails

66
Q

what are tonofilaments?

A

looping kertain IFs in hemidesmosomes and desmins

67
Q

What is EBS?

A

Epidermolysis bullosa Simpex (EBS)

aut dominant disase invovling mutaiotn of kertain gene in teh Basl skin layer

68
Q

Bio finding of EBS

A

Aberrant kertain filametns and disrupted keratin

69
Q

What happens with mechanical stress in EBS

A

an lead to ruptur of basal epithelial cells –> blistering and sloughign off of skin

70
Q

Why is EBS dangerous?

A

Rapid loss of fluids when skin isn’t intact

71
Q

What are neruofilament fucntions?

A

Major proteins in neurons

stabilize cell shape, long axonal region

Stable trasnit for year sbefore they reach end of axon

72
Q

when are NF modified

A

Post translationsioanlly (in axons, very phosphooryalated)

73
Q

What makes NF different from other IFs

A

Cross bridges

74
Q

What does GFAP expression lead to?

A

increase in Reactive Astrocyte and fomrs of cellular scar after injuries to CNS

75
Q

Where are GFAPs located?

A

Mature Astrocytes (supporting cells in brain)

Injury –> hypertrophyin CNS

76
Q

Where are primary brain turmos primarily dervied?

A

Astrocytes

77
Q

What makes Nuclear Lamins different from other Intermediate Fibers?

A

1) Longer central rod domain
(central rod domain is the same in all IFs)

2) Also, they have a Nuclear import signal –> enables poteins to be directed from Cytosol (translated)–> nucleus (
3) Form a sheetlike lattice, differnt from the IF networks of other ptoeins

Regulated by phosphorylation/dephosphorylation evens that are synchronized to events of mitosis (nuclear evelope dissoltuion and refomraiton in prophase and telophase)

78
Q

What regualtes assembly of lamins

A

phos/dephos synchronized to mitosis

79
Q

Structure of lamin

A

Sheetlike lattice, large central rod

CMCB Fall (17 decks)

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