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motility
movement of cell, movement of environment, movement of components
contractility
shortening of muscles = specialized motility
how do motor proteins work
convert ATP into physical movement by altering shape, then ATP gets hydrolyzed, repeat
motor domain
binds to filament, powered through ATP, "walks"
lever domain
undergoes conformational change
stalk domain
connect filament and cargo binding domains
tail and light chain domains
binds cargo
dynein
walks toward minus end, cilia and flagella
kinesins
walk toward plus end, mitosis
examples of where microtubule motility is used (4)
- fast axonal transport
- endomembrane transport
- cilia, flagella
- mitosis
where is microfilament based motility used
- muscle contraction
- cell crawling
axoneme
- bundled MT structure of 9 doublets
- extension of membrane, - has a central pair
- anchored to a basal body
basal body
- similar to centrosome (MTOC)
- 9 triplet MT in a circle with no central pair
primary cilia structure and function
- 9 doublet/triplet MT, lacking center pair
- serve as sensory structures
protofilament
"one strand" of repeating subunits for a MF, MT or IF
structure of flagellar axonemes
- 9+2 pattern
- doublets
- tubule A=complete, 13 protofilaments, sidearm projections for dyenein
-tubule B= incomplete, 10 protofilaments
- central two complete
radial spokes
extend from outer doublet MT to the central pair
- stabilizes structure, turns sliding structure into bending
how does an axoneme move
- dynein connects adjacent doublets
- the dynein movement causes sliding
- radial spokes turn slide to bend
alternating activation of dynein
the coordinated fashion of moving that allows for bending of the axoneme
rotating motion of dynein results in...
propeller motion (circular) in flagella, rowing motion in cilia
anterograde transport of MT
kinesins walking toward plus end
retrograde transport of MT
dynein walking toward negative end
fast axonal transport
- involves movement of vesicles and organelles along MT
- proteins must travel fast down axon, diffusion too slow
structure of kinesin 1
- heterotrimer
- 2 light chains, 2 heavy chains
- light chain: cargo
- heavy chain: bind and hydrolyze ATP, drive walking
what do the legs of kinase 1 bind to
beta tubulin subunits, 8nm increments
- 60-70% effective work output
describe the process of kinesin walking
1. leading heavy chain binds ATP
2. this causes trailing chain to move forward and bind to the next beta tubulin
3. new leading heavy chain release ADP, ATP on trailing chain hydrolyze ATP
what motor proteins are used with microfilaments
myosin
protrusions
what cells use to crawl, made with microfilaments (lamellipodia and filopodia)
steps of cell movement
1. cell protrudes lamellipodia and filopodia out front
2. attach
3.actin retrograde allows cell movement
cell attachment proteins and mechanism
protein: integrins on outside and inside of the cell
- they bind through chemical bonds
- new attachment at front means rear attachment must break
contraction of cell
rear of cell squeeze body forward and release rear attachments
Rho role in translocation
controls actin-myosin interactions
chemotaxis
- cell responds to chemical gradient
chemoattractant: moves toward an increase in ligands
chemorepellents: move toward low conc. of ligands
how are Rho family GTPase activated
through binding of molecules to cell surface (G-protein linked) receptors
what is smooth muscle responsible for and where is it found
involuntary, slow, lengthy contractions
found: hollow organ walls
Ca2+ role in muscle contraction
responds to nerve or hormone signals and enters muscle cell
calmodulin
protein that binds to Ca2+ in muscle cell
calcium-calmodulin complex
binds to MLCK during muscle contraction
MLCK
myosin light chain kinase
- triggers myosin-light chain phosphorylation (use ATP) which activates myosin2 makes a cross bridge with actin
cell crawling vs muscle contractions
lamellipodia and filopodia growth, myosin contraction
vs
actin and myosin contraction
regulatory light chains
a small polypeptide group bound that regulate ATPase at the motor domain
distance and grouping of myosin
short distnace, large array
distance and grouping of myosin
single or small groups, long distance
descending composition of a muscle
muscle, muscle fiber bundle, muscle fiber (muscle cell), myofibrils, bundles of thick and thin filaments in repeating units called sarcomeres
thick filaments in a muscle
myosin 2
thin filaments in a muscle
actin
z line
sarcomere divider
A band
myosin and actin overlap
I band
thin filaments only
H zone
space between negative actin filaments ends, myosin tails present
m line
middle of sarcomere
sarcoplasmic reticulum
specialized ER that surrounds myofibrils and associated with T-tubules, this ensures all myofibrils are able to receive calcium
Ca storage and release
scarcolemma
muscle cell membrane
tropomyosin
complexed with actin filament into a coil
troponins (T,I and C)
bind along filament to regulate myosin
T: bind tropomyosin
I: inhibitor
C: calcium binding
capZ
stabilizes plus ends and binds to alpha actinin
alpha actinin
anchors filament to z line
tropomodulin
binds free minus end to maintain length
myomesin
anchors the myosin tails to the m line
titin
flexibly links thick filament (myosin) to z line to keep them straight
nebulin
stabilize thin filament assembly
muscle contraction regulation
Ca2+ will bind to troponin and pull tropomyosin away from myosin binding sites
if low Ca2+ the sections will remain blocked
calcium release
occurs from internal stores in sarcoplasmic reticulum
ryanodine receptors (RyR)
Calcium-release channel of sarcoplasmic reticulum
how does the RyR complex work
electrical stimulus triggers voltage dependent partner protein allowing RyR to open and calcium to flow into the cytosol
how calcium enter SR again
electric stimulus stops, RyR channel close, calcium ATPase pumps calcium back into SR
cardiac muscle
function similarity to skeletal muscle
electrically coupled to have coordinated contraction
cardiac cell and calcium release
voltage gated channels release small amount of calcium which indirectly leads to large calcium release of ryanodine receptors