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BIO270H1 (61)


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Chris Garside

Lecture 7 Movement and Muscle Contraction  Cytoskeleton: i. Protein based ii. Microtubules and microfilament iii.Polarized to give directionality iv.Sets path for transfer v. Pulled to move proteins or skeleton vi.Reorganizes cytoskeletal network  Motor Proteins i. ATPase: enzyme convert energy from ATP hydrolysis into mechanical energy ii. Conformational Changes: move along cytoskeleton a. Myosin proteins move along actin base filaments b. Kinesin (+) and dynein (-) move along tubulin microtubules *Dyenin larger and faster than kinesm. Microtubules  Tubulin: a. b. Multiple isoforms c. Forms spontaneously d. Often anchored and polarized at both ends i. (-) End: mictrotubule organizing center (MTOC) near nucleus ii. (+) End: integral proteins in plasma membrane Growth and Shrinkage:  Treadmilling Range: i. (+) end: add tubulin ii. (-) end: lose tubulin *moves but length does not change Microtubule associated proteins (MAPS): STOPs stabilize + end Dynamic Instability: b-tubulin gtp hydrolyses destabilizes microtube structure (GTP stabilizes) Assembly of microtubules Cilia and Flagella:  Cilia: wavelike  Flagella: single or paired; whip, axonomal (9+2) Microfilaments - Composed of B-actin - Uses motor protein: myosin - Movement : i. Moves from B-actin polymerization ii. Sliding filament with myosin (a-actin) Growth and Structure of Microfilaments: Spontaneous Growth: 6-10x faster at +end Capping Proteins: Stabilize (-) end Cellular Microfilaments: structural  Tangled Network: linked by filamin protein  Bundles: cross-;inked by fascin protein **Network and bundles attached to plasma membrane by dystrophin Myosin: Motor protein - Sliding filament model - ATPase - 17 classes: i. Isoforms for each class and all have similar structure: a. Head: ATPase activity b. Tail: bind to subcellular components c. Neck: regulation of ATPase Sliding Filament Model: *Two processes 1. Chemical Reaction: binding of myosin to actin forming cross-bridges 2. Structural Change: myosin bends (power stroke) Actin Myosin Activity:  Unitary Displacement: how far each step is depends on myosin neck length and location sites on actin  Duty Cycle: cross bridge cycle time: 50% spent bound. Multiple heads maintain contact Muscle Cells (myocytes) ** contractile cell unique to animals  Thick Filament: myosin polymers: myosin II hexamers  Thin Filament: ii. A-actin polymer iii.Capped: Tropomodulin (-) and CapZ (+)  Troponin and Tropomyosin: proteins that mediate thick and think filament interaction Properties: - Striated: skeletal and cardiac muscles - Smooth muscle (no arrangement to actin and myosin) Muscle Type Movement Nucleus Skeletal voluntary Multiple Cardiac
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