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33 Cards in this Set
- Front
- Back
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Linear molecular motors are associated with polymeric filaments. Which filaments are myosins and kinesins associated with?
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Actin filaments are associated with myosins and microtubules are associated with kinesis and dynein
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Which molecular motor is found predominantly in muscle cells?
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Myosin II
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Describe the structure of myosin II
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•A chain with two heads on one end, each with an actin binding site, an ATP binding site and a flex point (some other domains as well)
•Thick filament structure: tail diameter 2 nm, thick filament backbone diameter 16.3 nm, thick filament and packed myosin heads 20.3 nm, length of native thick filaments 1.6 μm |
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Describe the structure of myosin filaments
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They are arranged tail to tail leaving the heads outward; and line up in an offset fashion
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Describe the structure of actin filaments
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G-actin monomers polymerize to form thin filaments
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What are sarcomeres?
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What causes depolarisation of the muscle cell membrane?
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Ca2+ influx in the depolarising nerve cell triggers release of acetylcholine at the neuromuscular junction. Ach binds with the sarcolemma triggering muscle fiber action potential.
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How does cell membrane depolarisation propagate?
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Along the cell surface as Na+ influxes by rapidly spreading regional depolarization
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Describe how calcium ions are released from intracellular calcium stores (sarcoplasmic reticulum). Which membrane-bound proteins are involved in this process?
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T-tubule system contains voltage-dependent calcium channels known as dihydropyridine receptors (DHP) which are activated by the end plate potential. These are mechanically linked to ryanodine receptors in the sarcoplasmic reticulum which open channels allowing the flow of Ca2+ from the sarcoplasmic reticulum into the cytoplasm
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Describe the fate of calcium ions during activation of the myofilaments.
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Ca2+ binds to troponin C by the actin filaments, which subsequently causes the troponin complex to pull tropomyosin away from the myosin binding sites on nearby actin filaments. Myosin cross-bridge binding sites on the actin filaments are now uncovered. By hydrolysing ATP, myosin can now cycle through attached and detatched states to actin causing concentration contraction provided the force exceeds the load.
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What happens to calcium ions during relaxation?
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In relaxation, [Ca2+] decreases, calcium dissociates from troponin, resulting in inactivation of myosin binding sites on actin, and muscle relaxation.
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What are the 3 key features of the cross-bridge cycle?
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ATP used in each cycle, one-way sliding (towards M-line), small step size during shortening
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What is the sarcolemma
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the plasma membrane of myofibers
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What is the sarcoplasm
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cytoplasm of myofibers
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motor unit
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one motoneurone and all the muscle fibres it innervates (the functional unit of normal skeletal muscle)
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Recruitment
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vary the number of motor units that are active and thus vary force
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How can action potentials be altered to increase, or summate, the force?
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Increase the frequency of action potentials (they are all the same size, too high a frequency causes tetanus
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What determines maximum isometric force?
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Filament overlap
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Define isometric, isotonic, and isovelocity
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isometric - force produced without a change in muscle length
isotonic - constant force with change in length isovelocity - force with constant velocity of shortening or lengthening |
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Define concentric and eccentric contraction
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In concentric contraction, muscle shortens, in eccentric contraction, muscle lengthens
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What kind of reaction allows energy transfer from ATP to a reaction?
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Hydrolysis
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What three processes is ATP used for in muscles?
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Energising myosin heads for 'power stroke' of contraction, disconnecting myosin head from actin, active transport of Ca2+ back into the sarcoplasmic reticulum
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Replenishment of ATP occurs via three processes at varying rates and efficacy, describe these
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Phosphocreatinine replenishes ATP IMMEDIATELY
Glycolysis replenishes ATP short term without O2 Oxidation replenishes ATP long term with O2 |
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Where is phosphocreatinine produced and how does it replenish ATP?
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Produced in liver and transported via blood for storage in muscles. It replenishes ATP by donating a phosphate (creatine phosphokinase) and becoming creatinine.
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Cardiac muscle features
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Small cells, action potentials spread between cells, some cardiac cell types have spontaneous action potentials. Calcium dependent calcium release.
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Can cardiac muscle tetanus?
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NOOOO
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Is smooth muscle striated and why or why not?
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Smooth muscle is composed of filaments, but they are not arranged in regular arrays so cells appear smooth, not striated, and form sheets, not fibers.
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Smooth muscle forms the walls of tubular organs such as (list 3)
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Blood vessels, GI tract, reproductive tract
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What triggers smooth muscle contraction?
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Smooth muscle contracts when Ca2+ binds to calmodulin, MLCK (myosin light chain kinase) activated, myosin is phosphorylated.
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twitch
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the contraction and relaxation of muscle
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fused tetanus
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the prolonged contraction of a muscle caused by rapidly repeated stimuli which cause action potentials to summate and elevate Ca2+ levels in the sarcoplasm
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Electromyogram
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Technique for evaluating and recording the electrical activity produced by skeletal muscles
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How long a muscle action potential last compared to how the muscle force response lasts (qualitatively)?
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The muscle action potential including the refractory period is slightly longer than the time force is exerted.
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