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MSK 2 > Contractile Proteins > Flashcards

Contractile Proteins Flashcards

1
Q

What do the structural, spatial, and mechanical functions of cells depend on?

A

Cytoskeleton

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2
Q

Allows cells to have:

  • organization in space
  • mechanical interaction with each other and their environment
  • ability to rearrange internal components in response to growth, division, and dynamic adaptation to changing situations
  • change shape in response to stimuli
  • migrate from place to place
  • have polarity
  • remain in close contact with each other and form stable sheets/layers
A

Cytoskeleton

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3
Q

Determine shape of cell, cell locomotion, and pinching of one cell into 2

A

Actin and actin-binding proteins

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4
Q

Molecular machines that convert biochemical energy from ATP hydrolysis to mechanical energy that moves organelles along filaments or move filaments on proteins

A

Myosin (motor proteins)

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5
Q

Actin subunit

A

G actin (globular actin)

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6
Q
  • 375 AA polypeptide carrying tightly associated ATP or ADP
  • small in size & diffuse rapidly into cytoskeleton
  • assembled/polymerized head to tail to form tight, right handed helix
A

G-actin

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7
Q

Right-handed G-actin helix

A

F actin (filamentous actin)

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8
Q

Polarity of F-actin

A
  • slow growing minus end

- fast growing plus end

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9
Q

Importance of polarity of actin filaments

A
  • assembly

- establishing unique direction of myosin movement relative to actin

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10
Q

Important mechanism by which cells control shape and movement

A

Regulation of actin filament formation

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11
Q
  • associate spontaneously
  • unstable
  • disassembly readily
A

Small oil Gomes’s

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12
Q

For new actin filaments to form, what must happen?

A

Filament nucleation

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13
Q

Filament nucleation

A

Subunits must assemble into an initial aggregate (nucleus made of 3 actin monomers) that is stabilized by multiple subunit-subunit contacts then elongate rapidly by addition of more subunits

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14
Q

How do actin filaments grow?

A

Reversible addition of monomers to both ends

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15
Q

Which end elongates faster?

A

Plus end elongates 5-10 x faster

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16
Q

Actin monomers have ___ which is hydrolyzed to _____ following filament assembly.

A
  • bound ATP

- hydrolyzed to ADP and Pi

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17
Q

Compare actin monomers to which ATP is bound vs. ones with bound ADP

A
  • ATP not required for polymerization

- Actin monomers to which ATP is bound polymerize more rapidly

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18
Q

Plays a key role in assembly and dynamic behavior of actin filaments

A

ATP binding and hydrolysis

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19
Q

Since actin polymerization is reversible, filaments can ____ as needed by the _____.

A
  1. Depolymerize

2. Dissociation of actin monomers

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20
Q

dependent on concentration of free monomers

A

Equilibrium between actin monomers and filaments

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21
Q

Rate at which actin monomers are incorporated into filaments is proportional to what?

A

Concentration

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22
Q

There is a _____ of actin monomers at which _______. At this concentration, monomers and filaments are in apparent _____.

A
  1. Critical concentration
  2. Rate of their polymerization into filaments equals rate of dissociation
  3. Equilibrium
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23
Q

The rate of subunit association is proportional to ______.

A

Concentration of free monomers

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24
Q

The rate of subunit dissociation is independent of _____.

A

Monomer concentration

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25
Q

K(off) = Cc x k(on)

A

An apparent equilibrium is reached at critical concentration of monomers (Cc)

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26
Q
  • organized into higher order structures, forming bundles of 3D networks within cells
  • associated with other cell structures such as the PM
  • abundant beneath PM, where they form network
A

Actin

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27
Q

Functions of actin

A
  • mechanical support
  • determines cell shape
  • allows movement of cell surface
  • enables cells to migrate, engulf particles, and divide
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28
Q

Regulates organization of actin network and functional structures

A

Actin binding proteins

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29
Q
  • helps achieve cross-linking of F-actin

- have at least 2 actin-binding domains

A

Accessory proteins

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30
Q

Nature of association of filaments is determined by?

A

Size and shape of the cross linking proteins

31
Q

Typically small ridged proteins that force filaments to align closely with each other

A

Bundling proteins

32
Q

Two types of structures that actin filaments are assembled into

A
  • actin bundles

- actin networks

33
Q

Actin bundles are cross-linked into _____

A

Closely-packed parallel arrays

34
Q
  • loosely cross-linked in orthogonal arrays that form 3-D meshwork with more flexible gel-like properties
  • makes cells flexible
  • changes polarity of actin filament
A

Actin networks

35
Q
  • parallel bundle

- tight-packing prevents myosin II from entering bundle

A

Actin filaments and fibrin

36
Q
  • contractile bundle

- loose packing allows myosin II to enter bundle

A

Actin filaments and alpha-actinin

37
Q
  • made of closely spaced actin filaments in parallel
  • fimbrin monomer binds to actin filaments
  • has 2 actin-binding domains (ABD)
  • holds 2 parallel filaments close together
  • filaments have same polarity
  • supports projections of PM
  • increase cell surface and gives structure stability
  • allows placement for additional receptors, channels for signaling ,transport, and uptake of nutrients
A

Parallel bundles

38
Q
  • loosely bundled actin filaments
  • looseness due to structure of cross-linking proteins 9ex: alpha-actinin)
  • binds as a diner
  • bigger protein = distance between actin bundles
  • filaments separated by greater distance
  • allows motor protein (myosin) to interact during contraction
  • contractile ring used in mitosis: allows squeezing of cytoplasm by contractile ring to cause cell division
A

Contractile bundles

39
Q
  • actin filaments in networks held together by large actin binding proteins
  • filaments
  • binds actin as a diner
  • actin binding domains located on opposite ends of the diner
  • creates a 3D meshwork
  • present in cells that need to withstand forces
A

Actin-bundling proteins

40
Q

Thin projections of PM supported by actin bundles. Formation and retraction of these structures is based on the regulated assembly and disassembly of actin filaments.

A

Filopodia

41
Q

Broad, sheet-like extensions at the leading edge of cell, containing network of actin filaments

A

Lamellipodia

42
Q

Based on actin filaments cross-linked into a 3D network, responsible for phagocytosis

A

Pseudopodia

43
Q

Spectrin

A

ABP contained by erythrocytes

44
Q
  • tetramers associate laterally
  • form actin network that creates cortical cytoskeleton
  • spectrin-actin network interacts with membrane proteins via interactions with ankyrin, protein 4.1
A

Spectrin

45
Q
  • mutations in erythrocytes cortical cytoskeleton proteins
  • hereditary spherocytosis (HS)
  • impaired deformability and reduced stability of RBCs
  • movement from large vessels to capillaries require flexibility and deformability
  • spherical RBCs
  • membrane breaks down, RBCs damaged and die
  • anemia
  • jaundice
  • splenomegaly
A

Hereditary spehrocytosis

46
Q
  • superfamily of motor proteins
  • 20 diff myosin types in eukaryotes
  • all move along actin filaments via ATP hydrolysis
A

Myosin

47
Q
  • bipolar filaments
  • tails associate to form shaft of filament
  • heads exposed at both ends
A

Skeletal muscle myosin II

48
Q

3 domains of myosin

A
  • head: contain actin binding and ATP binding sites, has ATPase activity
  • neck: flexible region, binds myosin light chain peptides
  • tail: intertwine to bring myosin head regions in close proximity, bind membrane/organelles
49
Q

Membrane association and endocytosis

A

Myosin I

50
Q

Contraction

A

Myosin II

51
Q

Organelle transport

A

Myosin V

52
Q

Myosin in the absence of ATP

A

Myosin attached to actin filament

53
Q

Myosin bound to ATP

A

Conformation change with release of actin

54
Q

What causes ATP hydrolysis?

A

Binding of actin

55
Q

What drives the “power stroke”?

A

Release of P and I elastic energy > straightens myosin > moves actin filament left

56
Q

Steps of the power stroke

A
  1. ATP binds and the head is released from actin
  2. Hydrolysis of ATP to ADP and Pi; myosin head rotates into “cocked” state
  3. Myosin head binds actin filament
  4. “Power stroke” = release of P and i elastic energy straightens myosin; moves actin filament left
  5. ADP released, ATP bound, head released from actin
57
Q

Power stroke (Velocity) mechanism is proportional to _____.

A

Length of neck domain

58
Q
  • thick filaments = 6 myosin polypeptide chains (1 pair of heavy chains which form the tail and 2 pairs of light chains which form the head)
  • thin filaments = 3 proteins = actin, tropomyosin, troponin
A

Skeletal muscle

59
Q

Skeletal muscle fiber at rest

A
  • myosin binding sites covered by tropomyosin so actin/myosin cannot interact
  • troponin is calcium-binding protein that helps initiate contraction
60
Q

Unit of skeletal muscle

A

Sarcomere

61
Q

Non-muscle cell contractions

A
  • contain several types of actin-myosin structures similar to skeletal muscle fibers (less stable/organized)
  • formed in transient manner as needed by cell
62
Q
  • bundles of F-actin and myosin II form contractile ring

- myosin movement along actin filaments creates cleavage furrow

A

Cytokinesis

63
Q

____ carries cargo along actin filaments.

A

Myosin V

64
Q
  • part of protein complex that linked cytoskeleton of muscle fibers to the surrounding CT
  • long protein with numerous redundant coils that provides a structural link b/w cytoskeleton of the muscle cell and the ECM
A

Dystrophin

65
Q
  • acts like shock absorber during contraction

- stabilizes the sarcolemma and prevents contraction-induced injury

A

Long protein with numerous redundant coils that provides a structural link b/w cytoskeleton of the muscle cell and the ECM

66
Q

Without functional dystrophin to support muscle strength and stability, muscle fibers are _____.

A

Easily damaged

67
Q

Loss of dystrophin

A

Duchenne’s muscular dystrophy

68
Q
  • X-linked recessive disorder
  • abnormal dystrophin gene
  • progressive muscle wasting
A

DMD (Duchenne’s Muscular Dystrophy)

69
Q

Milder form of DMD

A

Becker Muscular Dystrophy (BMD)

70
Q
  • connects cytoskeleton to basal lamina
  • stabilizes PM
  • hundreds of mutations
A

Dystrophin

71
Q
  • Little to no expression of dystrophin

- OOF mutants

A

Duchenne Muscular Dystrophy (DMD)

72
Q
  • Smaller protein with partial function of dystrophin

- IF mutation

A

Becker Muscular Dystrophy (BMD)

73
Q

Drugs being developed to treat dystrophin

A
  • gene therapy
  • dystrophin replacement
  • drugs to prevent exon skipping

MSK 2 (12 decks)

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