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MSK Exam 2 > Contractile Proteins > Flashcards

Contractile Proteins Flashcards

1
Q

The Cytoskeleton

A

Define the stability, structure, shape, and is very dynamic

Structural, spatial and mechanical functions of cells depend on the cytoskeleton, a remarkable system of filaments scaffolding the cell

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2
Q

Actin

A

major compotent of the cytoskeleton

each subunit is called a G actin (globular)

has a tightly associated ATP or ADP

they polymerize head to tail to form a right handed helix called a filamentous actin (microfilaments) or F actin

filaments are polar with a slower growing minus end and a faster growing plus end

important in establishing myosin movement relative to actin

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3
Q

Assembly of actin polymers

A

small oligomers are unstable until they form an initial aggregate (3 monomers)

3 phases: nucleation, elongation, steady state

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4
Q

Process of assembly and dissasembly

A

actin has a bound ATP and it is hydrolyzed to ADP and Pi following assembly

ATP not necessary but ATP makes the process much faster

can also depolymerize as needed

an equillibrium exists between actin monomers and filaments and is dependant on the concentration of free monomers

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5
Q

Critical concentration

A

rate of actins polymerization into filaments is equal to the rate of dissociation

this is considered equilibrium

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6
Q

equation of polymerization of Actin monomers

A

k off = C x k on

C=the concentration of free monomers

k on is dependant of the concentration and that is the rate of association

k off is independant of the C and is the rate of dissociation

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7
Q

what makes up the 3 D structure of Actin filaments

A

THe actin filaments are organized into higher order structures that are regulated by actin binding proteins

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8
Q

Where are actin filaments particulary abundant

A

beneath the plasma membrane
where they provide mechanical support, detemine the cell shape, and allow movement of the cell surface allowing for cells to migrate and engulf particles and divide

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9
Q

What are three cross linking proteins of actin filaments

A

alpha-actin
filamin
spectrin

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10
Q

Actin bundles

A

cross link into closely packed parallel arrays
polarity of actin filaments

consist of Parallel bundles
and contractile bundles

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11
Q

Parallel bundle

A

closely spaced actin filaments in parallel

fimbrin monomer binds to actin filaments

has 2 actin binding domains

holds two parrallel filaments close together

increases the cell surface area allowing for additional receptors and channels which facillitated signaling transport and uptake of nutrients

supports projections of plasma membranes like microvilli

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12
Q

Contractile bundles

A

loosely bundled actin filaments

alpa-actin
this is a bigger protein so it allows for the filaments to be seperated by a greater distance

allows motor protein to interact during contraction

contractile ring used in mitosis

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13
Q

filamin

A

binds actin as a dimer and helps create a 3D meshwork

present in cells that need to withstand forces

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14
Q

filopodia

A

thin projections of the plasma membrane supported by actin bundles

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15
Q

Lamellipodia

A

broad sheet like extensions at the leading edge of cell, containing a network of actin filaments

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16
Q

Pseudopodia

A

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

17
Q

Erythrocytes

A

have a strong cytoskeleton consisting of spectrin, ankrynin, and protein 4.1

important for the three dimensional shape of the erythrocyte

18
Q

Hereditary Spherocytosis

A

mutation in the erythrocyte cotrical cytoskeleton proteins: Spectrin, ankyrin, Protein 4.1

impaired deformabillity

makes the RBCs spherical leading to membrane breakdown and Damge to RBCs

not bi-concave

anemia, jaundice, splenomegaly

19
Q

Myosin

A

Motor protein

move along actin filaments via ATP hydrolysis

Skeletal Muscle Myosin II

20
Q

three major parts of Myosin

A

Head: contains the actin binding and ATP binding sites, also has ATPase activity

Neck: Flexible region
binds myosin light chain peptides

Tail: intertwine to bring myosin head regions in close proximity
bind membrane/organelles

21
Q

Myosin I

A

has only one head
one heavy chain
one light chain

function is for membrane association, and endocytosis

22
Q

Myosin II

A

2 heavy chain
2 light chain

used for contraction (muscle)

23
Q

Myosin 5

A

used for organelle transport

2 heavy chain
6 light chain

at the tail has a receptor that binds to a signal on a organelle

24
Q

Process of movement of the myosin along F actin

A

1) Binds ATP and the head dissociates from actin
2) hydrolysis of ATP to ADP and Pi and the myosin cocks its head
3) Myosin binds the actin filament
4) release of the Pi causes a straightening of the bound myosin causing the power stroke moving the myosin
5) ADP released and the whole process restarts

25
Q

WHat is the velocity of the powerstroke based on

A

velocity of the movement is proportional to the length of the neck

longer neck the faster the movement

26
Q

THick filaments composed of:

A

6 myosin polypeptide chains

27
Q

THin filament composed of

A

actin, tropomyosin, and troponin

28
Q

important proteins in sarcomere

A

CapZ- binds the actin on the plus end

Tropomodulin- bind to the minus end of the actin

Nebulin- caps the minus end to prevent disassembly

Titin- gives more contractillity

29
Q

Contraction of smooth muscle

A

similar to skeletal but the smooth doesnt have tropomyosin but has calmodulin

calcium binds calmodulin which causes a conformational change which will bind to myosin light chain and then will phosphorylate to the active myosin light chain and that will cause the power stroke

dephospho form does not

30
Q

Non muscle cell contraction

A

much less stable or organized

cytokinesis

bundles of F actin and myosin form contractile ring

alpha actinin

myosin moving along causes the pinching

31
Q

Dystrophin

A

links the cytoskeleton of muscle fibers to the surrounding connective tissue and the extracellular matrix

this interaction acts as a shock absorber

stabilizes the sarcolemma

connects the PM to the actin filaments

32
Q

Duchene Muscular Dystrophy

A

X linked recessive disorder

abnormal dystrophin

progressive muscle wasting

wheelchairs by age 12 and die of respiratiry failure by age 22

Milder form with later onset Becker muscular dystrophy

33
Q

how is dystrophin disrupted

A

DMD are out of frame mutations- little to no expression of dystrophin

BMD: in frame mutation- smaller protein with partial function

large internal deletions and lead to muscle degeneration

gene therapy
dystrophin replacement

MSK Exam 2 (19 decks)

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