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MSK Exam 1 > Lecture 17: Contractile Protiens > Flashcards

Lecture 17: Contractile Protiens Flashcards

1
Q

Actin

What does this cytoskeletal protein determine?

A
  • Shape of the Cell
  • Cell Locomotion
  • Pinching of One Cell into two
    • Mitosis
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2
Q

Myosin

What is this cytoskeletal protein functions?

A
  • Use ATP to move organelles along filaments
  • Use ATP to move filaments on proteins
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3
Q

On which end of actin do we typically see growth?

A

The plus end

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4
Q

In G Actin, where can you find ATP?

A

In the ATP cleft, which faces the minus end

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5
Q

How does actin assemble into a filament?

A
  • Stage 1: Nucleation (Lag Phase)
    • ​Small acting oligomers must first form an aggregate of 3 actin monomers
    • Each aggregate must be stabilized
  • Stage 2: Elongation (Growth Phase)
    • ​Multiple subunits contract and elongate rapidly
    • If actin is bound to ATP, polymerization happens much more quickly
  • Stage 3: Steady State (Equilibrium)
    • ​Depends on concentration of free actin
    • Rate of polymerization = Rate of depolymerization
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6
Q

What is the difference between the rate of subunit association and dissociation?

When is equilibrium reached between the two?

A
  • Subunit association: Proportional to concentration of free monomers
    • C x kon
  • Subunit dissociation: Independent of monomer concentration
  • Equilibrium: Reached at critical concentration of monomers
    • koff = Cc x kon
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7
Q

Where can you find actin filaments?

A
  • Beneath plasma membrane
  • Mechanical Support
  • Determining Cell Shape
  • Movement of Cell Surface
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8
Q

What determines the nature of the association of actin filaments?

How is cross linking achieved in F-actin?

A

The size and shape of the actin binding proteins

Acessory Proteins

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9
Q

What is the basic organization of actin parallel bundles?

What monomer binds the parralel bundles?

A
  • Actin fibers are crosslinked together with all of their plus and minus ends on the same side.
  • Parallel fibers are very close and doesn’t allow Myosin II from entering the bundle
  • Fimbrin binds actin
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10
Q

Where in the cell can you find actin parallel bundles?

What do they do?

A

Location

  • Projections of Plasma Membranes
  • Microvilli
  • Cell Cortex
  • Adherens belt

Functions

  • Placement of receptors and channels
    • Facilitate signaling, transport, uptake of nutrients
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11
Q

What is the basic organization of actin contractile bundles arrays?

What monomer binds the contractile bundles?

A
  • Actin fibers are crosslinked together with all of their plus and minus ends on the same side.
  • Parallel fibers are very loose and allows Myosin II from entering the bundle
  • α-Actinin binds actin
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12
Q

What does actin contractile bundles do?

A

Functions

  • Moving endocytic vesicles
  • Squeezing of cytoplasm by contractile ring to cause cell divison
  • Can also aid muscle contraction
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13
Q

What is a contractile ring made of?

A

Actin and Myosin II

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14
Q

What is the basic organization of actin bundling proteins?

What monomer binds this network?

A
  • Actin fibers are held together in flexible 3-d meshowrks
  • Filamin binds actin as a dimer
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15
Q

For Filamin:

Where are its actin binding domains located?

A

At the farthest ends of a dimerized structure

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16
Q

What is the organizational name for actin networks’ three dimensional meshworks?

A

Orthogonal Arrays

17
Q

Where in the cell can you find actin bundle networks?

What do they do?

A

Location

  • Filopodia: finger like prjoections
  • Lamellopodia: sheet like extensions
  • Pseudopodia: cross linking

Functions

  • Phagocytosis
  • Movement
18
Q

What -podia are commonly associated with phagocytosis?

A

Pseudopodia

19
Q

Erythrocytes contain spectrin:

What does it do?

What does it interact with and how?

A
  • Forms the actin network that makes up the cortical cytoskeleton
  • Interacts with membrane proteins via ankryin and protein 4.1
20
Q

What is deficient in Hereditary Spherocytosis?

What happens to the RBC?

A

Cortical skeleton proteins of the red blood cells

  • Spectrin
  • Ankryin
  • Protein 4.1

Loss of these proteins reduces RBC stbility and cannot move from large vessels to capillaries due to lack of flexibility and deformability

21
Q

Briefly, how does myosin move?

A

Along actin filaments via ATP hydrolysis

22
Q

How is myosin organized?

A
  • Head Region
    • Actin and ATP binding sites
    • ATPase activity
  • Neck Region
    • Flexible
    • Binds myosin light chain peptides
  • Tail Region
    • Can Bring myosin head in closer proximity
    • Binds membrane/organelles
23
Q

What are the freatures and function of Myosin I?

A

Myosin I

  • 1 Light Chain in neck
  • 1 Heavy Chain in tail
  • Function: Membrane association and endocytosis
24
Q

What myosin is most common in skeletal muscles?

What is its features and function?

A

Myosin II

  • 2 Light Chains in neck
  • 2 Heavy Chains in tail
  • Function: Contraction
25
Q

What are the freatures and function of Myosin V?

A

Myosin V

  • 6 Light Chains in neck
  • 2 Heavy Chains in tail
  • Function: Organelle Transport
26
Q

In more detail, how does a myosin move along F-actin?

What causes a myosin “power stroke?”

A
  • If there is no ATP around, myosin is attached to actin.
  • When ATP is bound, myosin releases actin
    • Myosin now in “cocked” state
  • ATP Hydrolysis: Power Stroke
    • The release of Pi gives off energy to move myosin on the actin filament
  • Will remain bound to new actin until ATP is bound again
27
Q

Which end of actin does myosin move towards?

A

The plus end

28
Q

What will a myosin with a longer neck have over a myosin with a shorter neck?

A

A Myosin with a longer neck will have a greater power stroke velocity (increased rate of movement)

(Keep in mind this is not referring to the length of the tail, but the light chain neck portion)

29
Q

What thin and thick filaments compose a skeletal muscle?

A
  • Thick: Myosin Chains
  • Thin: Actin, tropomyosin, toponin
30
Q

In a sarcomere, which side of the actin would be the plus side?

A

The side attached to the Z Disc

31
Q

In a sarcomere which side of the actin would be the minus side?

A

The side farthest from the Z Disk (in the A Band)

32
Q

Briefly, how does a skeletal muscle contract?

A
  • Activation of Voltage Gated Calcium allows calcium to enter the cell, prompting a release of Calcium from the Sarcoplasmic Reticulum to release its calcium
  • The outflow of calcium allows the myosin heads access to the actin cross-bridge binding sites, permitting muscle contraction.
    • It will bind to troponin to initiate contraction
33
Q

Briefly, how does a smooth muscle contract?

A
  • Calcium from the Sarcoplasmic Reticulum binds to calmodulin
  • This complex binds to Myosin Light Chain Kinase
    • Result: Active Mysoin Light Chain Kinase
  • With ATP, there is phosophyrlation of myosin light chain
    • Contraction occurs
34
Q

What enzyme in smooth muscle activates myosin?

A

Myosin Light Chain Kinase

35
Q

What contributes to the prevention of myosin binding to actin in smooth muscle?

What enzyme causes this inhibitory state?

A

Folding of the myosin by the regulatory light chains in the neck

Myosin Light Chain Phosphatase

36
Q

What does the Dystrophen protein do?

A
  • Connects Cytoskeleton to the basal lamina
  • Stabilizes the membrane
    • Helps to relieve the stress of contraction by spreading the forces out
  • Shock absorber during contraction
37
Q

What is the heredity of Duchene’s Muscular Dystrophy?

What is its symptoms?

A
  • X Linked Recessive
  • Muscle Wasting
  • Normally will die in young adulthod

MSK Exam 1 (41 decks)

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