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MSK1 > Contractile proteins > Flashcards

Contractile proteins Flashcards

1
Q

What is the cytoskeleton?

A

System of filaments scaffolding the cell that helps with structural, spatial and mechanical functions

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2
Q

What is a major component of the cytoskeleton?

A

Actin

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3
Q

What determines the shape of the cell and its ability to divide?

A

Actin and actin binding proteins

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4
Q

What uses ATP hydrolysis to move filaments and move organelles along filaments?

A

Myosin (motor protein)

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5
Q

Each subunit of actin is bound to what and called?

A

G-actin (globular actin) is bound to an ATP

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6
Q

G-actin subunits assemble into what and are bound to what?

A

F-actin (filamentous actin) is bound to ADP after it hydrolyzed it to help form a filament

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7
Q

Which end of the F-actin grows faster?

A

Plus end grows faster and minus end grows slower

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8
Q

Why is polarity of the F-actin important?

A

It is important for assembly and for establishing a direction of movement of myosin relative to actin

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9
Q

What are the phases of F-actin polymerization?

A 
Nucleation (lag phase)
Elongation (growth phase)
Steady state (equilibrium phase)
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10
Q

Describe the polymerization of F-actin

A

G-actin subunits form an oligomer of 3 subunits and then logarithmically grow fast into F-actin

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11
Q

What is the critical concentration of actin?

A

When the rate of polymerization is equal to the rate of dissociation of actin (steady state)

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12
Q

Where is actin the most abundant?

A

Right beneath the plasma membrane to provide mechanical support, cell shape and enables cells to migrate, engulf, divide

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13
Q

Actin binding proteins

A

Organize f-actin into bundles/networks that can then perform the functions of actin - have to have 2 actin binding domains

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14
Q

What are the 2 types of actin bundles?

A

Parallel bundle and contractile bundle

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15
Q

What protein is used in the parallel bundle?

A

Fimbrin

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16
Q

Describe parallel bundles?

A

Actin filaments + fimbrin; Tightly packed to prevent myosin 2 from entering; seen in microvilli to increase surface area, nutrient uptake and signaling of the cell

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17
Q

What protein is used in the contractile bundle?

A

Alpha-actinin

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18
Q

Describe contractile bundles?

A

Actin filaments + alpha-actinin; loosely packed to allow myosin 2 to enter; seen in the contractile ring used in mitosis to divide the cell

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19
Q

Compare the size of alpha-actinin

A

Larger protein in order to increase the distance between actin filaments

20
Q

What are actin networks?

A

Actin filaments held together by large actin binding proteins such as filamin that creates a 3D meshwork in order to withstand force and determine stability of membrane

21
Q

What is spectrin?

A

Actin binding protein in RBCs that also binds ankyrin and protein 4.1 to control cell deformability/flexibility

22
Q

Hereditary spherocytosis

A

Mutations in spectrin, ankyrin, protein 4.1 that results in impaired deformability/flexibility leading to unstable RBCs = spherical RBCs

23
Q

What are the symptoms of HS?

A

Jaundice, splenomegaly, anemia and spherical RBCs

24
Q

What are myosin proteins?

A

Motor proteins that move along actin filaments via ATP hydrolysis

25
Q

What are the 3 domains of a myosin protein?

A

Head, neck, tail

26
Q

Purpose of the myosin head?

A

Contains actin binding sites and ATP binding sites as well as ATPase activity

27
Q

Purpose of myosin neck?

A

Flexible region that binds myosin light chain peptides

28
Q

Purpose of myosin tail?

A

Intertwine, bind membrane and organelles

29
Q

What are the 3 types of myosin?

A

Myosin 1, 2, 5

30
Q

Describe myosin 1

A

One head

Function = membrane association and endocytosis

31
Q

Describe myosin 2

A

2 heavy chains each with head and neck domain; tail homodimerizes
Function = contraction

32
Q

Describe myosin 5

A

2 heavy chains and 6 light chains per neck, end of tails associate with specific receptors on organelles
Function = organelle transport

33
Q

What direction do myosin proteins move?

A

Towards the plus end of actin

34
Q

How is the powerstroke related to the myosin neck?

A

The longer the myosin neck, the greater the rate of movement

35
Q

What are the important proteins within the sarcomere?

A

Cap Z, Tropomodulin, nebulin, Titin

36
Q

Cap Z function

A

Stabilizes plus end of sarcomere

37
Q

Tropomodulin function

A

Stabilizes minus end of sarcomere

38
Q

Nebulin function

A

Extends along the length of the actin filament; length determines the length of the actin filament

39
Q

Titin function

A

Stabilizes myosin and prevents overstretching

40
Q

What can titin mutations cause?

A

Cardiomyopathies - harder for heart to pump blood

41
Q

How do non-muscle cells contract?

A

Actin-myosin structures are formed in a transient manner as needed by the cell

42
Q

Describe the dystrophin protein?

A

Links the cytoskeleton (actin) of muscle fibers to the cell membrane/connective tissue
Acts as a shock absorber during contraction and stabilizes the sarcolemma to prevent injury to the muscle fibers

43
Q

What are the 2 types of duchenne’s muscular dystrophy?

A

Duchennes and beckers muscular dystrophy

44
Q

How is duchenne’s muscular dystrophy inherited?

A

X-linked recessive that causes muscle wasting

45
Q

What kind of mutations does duchenne’s muscular dystrophy have?

A

Out of frame mutants that create little to no dystrophin

46
Q

What kind of mutations does becker’s muscular dystrophy have?

A

In frame mutants that create a smaller protein with partial function

47
Q

What is the current treatment for duchenne’s muscular dystrophy?

A

Gene therapy, dystrophin replacement, drugs to prevent exon skipping

MSK1 (29 decks)

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