Hosam Mohamed-
cytoskeletal, motor protein element
What are intracellular elements that govern movement?
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actin, intermediate, microtubules
Order the three classes of cytoskeleton elements in order of thinnest to largest.
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Steps of Microtubule formation
1.alpha & beta combine to form tubulin
2.polarity occurs on each dimer, added end to end
3.negative end and positive end
4.chain length grows until reaches critical length
5. protofilaments line up side by side to form a sheet
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alpha tubulin bound GTP; beta tubulin bound GDP
Polarity occurs on each dimer ___________ and ____________
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more dimers are added and chain increases in length
At high concentration of tubulin,
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dimers are removed causing tubule to shrink
At low concentration of tubulin,
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by balancing growth and shrinkage, while hydrolyzing GTP
How do microtubules maintain their constant length?
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static systems
Systems in motion are much easier to alter than _______
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MAPs
-prevent microtubules from fully dissociating
-impairs many cellular processes-including cell division
-bind to the surface of microtubules; chief stabilizing or destabilizing structures
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protein kinases, phosphatases
MAPs are regulated by ________
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regulate cell division; ensure cell components are equally divided between daughter cells
How do hormone signaling pathways alter microtubule structure?
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regulate MAP structure and activity
How do cytokines alter microtubule structure?
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kinesin, dynein
What are the 2 major motor proteins associated with microtubules?
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undergo conformational changes, stretch out to grab tubulin dimer, then bend to pull themselves along microtubule
How do kinesin and dynein work?
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ATP hydrolysis
Structural changes in motor protein are __________ dependent.
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atpase domains of the proteins, regulatory proteins
Rate of movement in motor proteins is determined by:
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MTOC
negative tubules are arranged at _____
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outer edges of cell
positive tubules are located at _____
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directional movement
Microtubule polarity allows for ___________ of cargo
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Kinesin
-long neck
-fan-like tail that attaches to cargo
-globular head has ATPase activity; attaches to microtuble
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moves cargo in + direction to outer edges of cell
Kinesin function?
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5x faster, larger, moves in - direction to MTOC, doesn't attach directly to cargo
Major differences that Dynein has compared to kinesin?
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Cytoplasmic dynein
-involved in intracellular movement
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Axonemal dynein
- the driving force of cilia and flagella movements
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ATP binds; causing myosin to detach, myosin head extends and attaches to adjacent actin, release of phosphate promotes power stroke, adp is released
What are the steps in sliding filament model?
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no ATP, myosin
Rigor mortis is caused by _______ in ATP; causes _______ to remain firmly attached to actin
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Na enters the cell; depolarization occurs
What happens when acetylcholine binds to a cell?
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contractility, excitability, extensibility, elasticity
What are some special features of muscles?
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skeletal muscle
-long and cylindrical, in bundles
-multinucleated
-contains obvious striations
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cardiac muscle
-branching, chains of cells
-single or binucleated
-striations
-connected by intercalated discs
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Smooth muscles
-single cells, uninucleated
-no striations
-2 layers (opposite orientation)
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sarcolemma
-plasma membrane of muscle cells
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sarcoplasm
-cytoplasm of muscle cells
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sarcoplasmic reticulum
-specialized for the storage of calcium
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epimysium
-dense regular CT surrounding entire muscle; overcoat
-outside the muscle
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perimysium
-around the muscle
-surrounds groups of muscle cells (fascicles)
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endomysium
-fine sheath of CT that surrounds each muscle fiber
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sarcomeres
Myofibril is made up of repeating segments called ________
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sarcomere
-functional units of skeletal muscle tissue
-responsible for contraction
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Myofibrils
-long rods within cytoplasm
-make up 80% of sarcoplasm
-specialized contractile organelles found in muscle tissue
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A bands
-full length of the thick filament; includes inner end of thin filaments (dark region)
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depolarization; sarcolemma
Muscle excitation is controlled by a ________ of ______
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EC coupling
-the translation of an excitatory signal at the sarcolemma into a stimulation of contraction
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Ca2+
Increased intracellular _______ activates the actin-myosin machinery to induce contraction
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troponin, tropomyosin
Ca2+ signal is transmitted to contractile apparatus by thin filament proteins _______ and _________
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roll out of the way
When Ca2+ rises, they _______, allowing myosin to bind to actin
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troponin tropomyosin, sits, blocks
When Ca2+ is low, the ________ ________ complex _________ on the thin filament in a position that __________ actin's binding site for myosin
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Troponin C
- Ca2+ sensor; has 4 Ca2+ binding sites
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Troponin I
- links troponin to actin; inhibits actin-myosin ATPase
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Troponin T
-blocks sites on actin where myosin binds
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Voltage-sensitive Ca2+ channels
-allow the influx of Ca2+ into the cell from the extracellular space; Ca2+ comes in through DHP receptors
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motor end plate
- axon terminals that contain acetylcholine receptors
-when ACh binds; Na+ channels open
-Nicotinic Ach receptors initiate a wave of depolarization
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through multiple innervations, through transverse tubules
What are the 2 main ways that muscles are able to ensure that the entire sarcolemma is depolarized uniformly?
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DHP
-located in sarcolemma
-Ca2+ delivery is slow; it is used to induce opening of ryanodine
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Ryanodine receptor
-located in Sarcoplasmic reticulum; most skeletal muscles and cardiac muscles cause the signal to release greater amounts of Ca2+ from intracellular stores
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Calmodulin/calsequestrin
protein that binds calcium
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Ca2+ATPase ; Ca2+
Sarcolemma and SR activate _______ that pumps ________ out of the cell using the energy of ATP hydrolysis
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Na+ Ca2+ exchanger
-transporter located in the sarcolemma that exchanges Na+ for Ca2+
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extracellular; enter; intracellular
Reversible exchanger allows _________ Ca2+ to ______ the cell in exchange for _________ Na +
