Contractile Proteins Flashcards
which type of actin has polarity: globular or filamentous?
filamentous
actin bundles
cross-linked actin into closely packed parallel arrays
actin networks
loosely cross-linked actin into orthogonal arrays that form 3D meshworks with gel-like properties
- more flexible
actin-bundling proteins
small, ridged proteins that force the filaments to align closely with each other
- cross-links actin
- determines the nature of association of filaments
fimbrin
actin-bundling protein; binds to actin filaments as a monomer; holds two parallel filaments closely together
- ex: microvilli
contractile bundles of actin
loosely bundled actin
- ex: contractile ring used in mitosis
alpha-actinin
actin bundling protein; allows motor protein (myosin) to interact during contraction; binds as a dimer; filaments of actin are separated by a greater distance which allows myosin to interact during contraction
filamin
actin bundling protein; binds actin as a dimer; can create 3D meshwork
spectrin
actin binding protein in RBCs; forms actin network that forms a cortical cytoskeleton; this network interacts with membrane proteins via interactions with ankyrin, protein 4.1
hereditary spherocytosis
decrease flexibility and stability of RBCs; caused by mutations in the cortical cytoskeleton proteins in RBCs (spectrin, ankyrin, 4.1)
- Sx: jaundice, anemia, splenomegaly
pseudopodia
type of actin projection that is responsible for phagocytosis
lamellipodia
broad, sheet like extensions of actin at the leading edge of a moving cell
filopodia
thin projections of plasma membrane supported by actin bundles; formation and retraction of filopodia is based on regulated assembly and disassembly of actin filaments
what driving force allows myosin to move along actin filaments
ATP hydrolysis
head domain of myosin
- two parts
contains actin binding and ATP binding sites; ATPase activity
neck domain of myosin
the flexible region; binds myosin light chain peptides
tail domain of myosin
intertwines to bring myosin head regions in close proximity; binds membranes and organelles
skeletal muscle myosin I
- neck size
- function
- 10-14 (small)
- interacting with membranes, endocytosis
skeletal muscle myosin II
- neck size
- function
- 8 nm (v small)
- skeletal muscle contraction
skeletal muscle myosin V
- neck size
- function
- 36 nm (v long)
- organelle transport
how does rigor mortis occur
absence of ATP in the muscle –> myosin attaches to actin filaments and contracts and cannot relax
what happens when ATP binds to myosin
a conformational change occurs causing release of actin; myosin then remains in “cocked state” –> binds to actin causing release of Pi (energy) –> “power stroke”
“power stroke” of myosin bound to actin
release of P and i elastic energy which straightens myosin; moves actin filaments to the left
as length of neck domain of myosin increases, ____
rate of movement increases
what form is myosin in during low Ca2+ environements
folded
what phosphorylates myosin
MLC (myosin light chain) kinase
phosphorylation of myosin by MLC kinase causes ___
unfolding and activation of myosin
what activates MLC kinase
calcium
what dephosphorylates myosin
MLC (myosin light chain) phosphatase
dephosphorylation of myosin causes
folding and relaxation of myosin (inactive)
what causes the cleavage furrow in cytokinesis
myosin movement along actin filaments
difference between myosin VI and myosin V in moving across filamentous actin
myosin VI moves towards the (-) end
myosin V moves towards the (+) end
difference between dynein and kinesin in moving across filamentous actin
dynein moves toward (-) end
kinesin moves toward (+) end
Duchenne Muscular Dystrophy
- type of disorder
- what is it
- X-linked recessive
- progressive muscle wasting due to mutations within dystrophin gene
in-frame mutations in the dystrophin gene cause
becker muscular dystrophy
out of frame mutations in the dystrophin gene cause
duchenne muscular dystrophy
function of dystrophin
connects cytoskeleton to basal lamina; stabilizes the membrane of muscle cells
