CELL 201- motility and contractility

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68 Terms

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motility

movement of cell, movement of environment, movement of components

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contractility

shortening of muscles = specialized motility

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how do motor proteins work

convert ATP into physical movement by altering shape, then ATP gets hydrolyzed, repeat

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motor domain

binds to filament, powered through ATP, "walks"

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lever domain

undergoes conformational change

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stalk domain

connect filament and cargo binding domains

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tail and light chain domains

binds cargo

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dynein

walks toward minus end, cilia and flagella

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kinesins

walk toward plus end, mitosis

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examples of where microtubule motility is used (4)

- fast axonal transport

- endomembrane transport

- cilia, flagella

- mitosis

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where is microfilament based motility used

- muscle contraction

- cell crawling

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axoneme

- bundled MT structure of 9 doublets

- extension of membrane, - has a central pair

- anchored to a basal body

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basal body

- similar to centrosome (MTOC)

- 9 triplet MT in a circle with no central pair

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primary cilia structure and function

- 9 doublet/triplet MT, lacking center pair

- serve as sensory structures

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protofilament

"one strand" of repeating subunits for a MF, MT or IF

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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

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radial spokes

extend from outer doublet MT to the central pair

- stabilizes structure, turns sliding structure into bending

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how does an axoneme move

- dynein connects adjacent doublets

- the dynein movement causes sliding

- radial spokes turn slide to bend

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alternating activation of dynein

the coordinated fashion of moving that allows for bending of the axoneme

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rotating motion of dynein results in...

propeller motion (circular) in flagella, rowing motion in cilia

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anterograde transport of MT

kinesins walking toward plus end

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retrograde transport of MT

dynein walking toward negative end

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fast axonal transport

- involves movement of vesicles and organelles along MT

- proteins must travel fast down axon, diffusion too slow

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structure of kinesin 1

- heterotrimer

- 2 light chains, 2 heavy chains

- light chain: cargo

- heavy chain: bind and hydrolyze ATP, drive walking

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what do the legs of kinase 1 bind to

beta tubulin subunits, 8nm increments

- 60-70% effective work output

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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

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what motor proteins are used with microfilaments

myosin

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protrusions

what cells use to crawl, made with microfilaments (lamellipodia and filopodia)

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steps of cell movement

1. cell protrudes lamellipodia and filopodia out front

2. attach

3.actin retrograde allows cell movement

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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

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contraction of cell

rear of cell squeeze body forward and release rear attachments

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Rho role in translocation

controls actin-myosin interactions

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chemotaxis

- cell responds to chemical gradient

chemoattractant: moves toward an increase in ligands

chemorepellents: move toward low conc. of ligands

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how are Rho family GTPase activated

through binding of molecules to cell surface (G-protein linked) receptors

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what is smooth muscle responsible for and where is it found

involuntary, slow, lengthy contractions

found: hollow organ walls

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Ca2+ role in muscle contraction

responds to nerve or hormone signals and enters muscle cell

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calmodulin

protein that binds to Ca2+ in muscle cell

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calcium-calmodulin complex

binds to MLCK during muscle contraction

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MLCK

myosin light chain kinase

- triggers myosin-light chain phosphorylation (use ATP) which activates myosin2 makes a cross bridge with actin

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cell crawling vs muscle contractions

lamellipodia and filopodia growth, myosin contraction

vs

actin and myosin contraction

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regulatory light chains

a small polypeptide group bound that regulate ATPase at the motor domain

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distance and grouping of myosin

short distnace, large array

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distance and grouping of myosin

single or small groups, long distance

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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

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thick filaments in a muscle

myosin 2

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thin filaments in a muscle

actin

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z line

sarcomere divider

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A band

myosin and actin overlap

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I band

thin filaments only

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H zone

space between negative actin filaments ends, myosin tails present

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m line

middle of sarcomere

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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

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scarcolemma

muscle cell membrane

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tropomyosin

complexed with actin filament into a coil

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troponins (T,I and C)

bind along filament to regulate myosin

T: bind tropomyosin

I: inhibitor

C: calcium binding

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capZ

stabilizes plus ends and binds to alpha actinin

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alpha actinin

anchors filament to z line

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tropomodulin

binds free minus end to maintain length

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myomesin

anchors the myosin tails to the m line

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titin

flexibly links thick filament (myosin) to z line to keep them straight

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nebulin

stabilize thin filament assembly

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muscle contraction regulation

Ca2+ will bind to troponin and pull tropomyosin away from myosin binding sites

if low Ca2+ the sections will remain blocked

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calcium release

occurs from internal stores in sarcoplasmic reticulum

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ryanodine receptors (RyR)

Calcium-release channel of sarcoplasmic reticulum

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how does the RyR complex work

electrical stimulus triggers voltage dependent partner protein allowing RyR to open and calcium to flow into the cytosol

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how calcium enter SR again

electric stimulus stops, RyR channel close, calcium ATPase pumps calcium back into SR

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cardiac muscle

function similarity to skeletal muscle

electrically coupled to have coordinated contraction

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cardiac cell and calcium release

voltage gated channels release small amount of calcium which indirectly leads to large calcium release of ryanodine receptors