Transcript Muscles
Moyes and Schulte Chapter 6 Cellular Movement and Muscles Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Cellular movement Movement is a property of all cells Some cells (such as this amoeba) can move through their environment All cells can move components through the cytoplasm (such as the vesicles in this amoeba) Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Cytoskeleton and Motor Proteins All physiological processes depend on movement • Intracellular transport, changes in cell shape, cell motility, and animal locomotion All movement is due to the same machinery • Cytoskeleton – protein-based intracellular network • Motor proteins – enzymes that use energy from ATP Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Cytokeleton Composed of actin and microtubules Fluorescently labeled cell Actin – red Microtubules – green Nuclei - blue Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings The Cytoskeleton and Movement Three ways to use the cytoskeleton for movement • Cytoskeleton roadway and motor protein carriers • Reorganization of the cytoskeletal network • Motor proteins pull on the cytoskeletal rope Figure 6.1 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Microtubules Tube-like polymers of tubulin Organized into many arrangements Anchored near the nucleus and the plasma membrane • Microtubuleorganization center (MTOC) (-) • Integral proteins (+) Figure 6.2 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Microtubule Structure Polymers composed of the protein tubulin • Dimer of a–tubulin and btubulin Figure 6.4 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Microtubules Composition and Formation • Microtubules have a plus and minus end Figure 6.5 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Microtubules • Minus end of the microtubule is anchored at the Microtubuleorganization center (MTOC) • Plus end of the microtubules anchored by Integral membrane proteins at the plasma membrane Figure 6.2 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Microtubules can grow and shrink A microtubule can grow or shrink from either end “Dynamic Instability” Fig 6.6a Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Factors affecting Dynamic Instability • Local concentration of tubulin affects microtubule dynamics Figure 6.6 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Microtubule dynamics regulated by MAPs MAPs: Microtubule associate proteins Bind to microtubulues and stabilize or destabilize structure Figure 6.7 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Motor proteins Motor proteins can move along microtubules • alpha-Tubulin: pale blue • beta-Tubulin is pale green • Kinesin walks towards the plus-end of microtubules (right side of picture) Hoenger, A., Thormählen, M., Diaz-Avalos, R., Doerhoefer, M., Goldie, K.N., Müller, J. and Mandelkow, E. (2000) A new look at the microtubule binding patterns of dimeric Copyright © Education, publishing as Benjamin Cummings kinesins. J2005 MolPearson Biol, 297,Inc., 1087-103. Movement Along Microtubules Direction is determined by polarity and the type of motor protein • Kinesin move in + direction • Dynein moves in – direction Fueled by ATP Rate of movement is determined by the ATPase domain of the protein and regulatory proteins Dynein is larger than kinesin and moves 5times faster Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Microtubule Functions • Move subcellular components • e.g., Rapid change in skin color Figure 6.3 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Vesicle Traffic in a Neuron Figure 6.8 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Microtubule function - Cilia and Flagella • Cilia – numerous, wavelike motion • Flagella – single or in pairs, whiplike movement • Composed of microtubules • Arranged into axoneme • Movement results from asymmetric activation of dynein Figure 6.9 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Microtubules and Physiology Table 6.1 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Microfilaments Other type of cytoskeletal fiber Polymers composed of the protein actin Often use the motor protein myosin Found in all eukaryotic cells Movement arises from • Actin polymerization • Sliding filament model using myosin (more common) Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Actin filament Structure and Growth • Polymers of Gactin called Factin • Spontaneous growth (6-10X faster at + end) • Treadmilling when length is constant • Capping proteins increase length by stabilizing minus end Figure 6.10 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Microfilament Arrangement Figure 6.11 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Actin Polymerization Amoeboid movement Two types • Filapodia are rodlike extensions • Neural connections • Microvilli of digestive epithelia • Lamellapodia resemble pseudopodia • Leukocytes • Macrophages Figure 6.12 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Myosin – a motor protein Motor protein that works with actin filaments Most common type of movement Myosin is an ATPase • Converts energy from ATP to mechanical energy 17 classes of myosin with multiple isoforms Similar structure • Head, tail, and neck Figure 6.14 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Myosin as a motor protein Myosin moves along actin Analogous to pulling yourself along a rope • Actin: the rope • Myosin: your arm Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Sliding Filament model Figure 6.15 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Sliding Filament Model. Two processes • Chemical • Myosin binds to actin (Cross-bridge) • Structural • Myosin bends (Power stroke) Cross-bridge cycle • Formation of crossbridge, power stroke, and release Need ATP to attach and release Figure 6.15 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Variation in myosin function Two factors • Unitary displacement • Distance myosin steps during each crossbridge cycle • Depends on • Myosin neck length • Myosin placement (helical structure of actin) • Duty cycle • Cross-bridge time/cross-bridge cycle time • Typically 0.5 • Use multiple myosin dimers to maintain contact Figure 6.16 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings Sliding filament assay Figure 18-22, Lodish 4th edition. Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings The sliding-filament assay Actin and Myosin Function Muscle contraction Table 6.2 Copyright © 2005 Pearson Education, Inc., publishing as Benjamin Cummings