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Lecture 3

Winter Term -Week 3 Lecture Notes

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BIOL 103
Virginia K Walker

Movements and Muscle Control • Plants use turgor pressure and protists can move using cilia or flagella • Animals move using contractile proteins in microfilaments Homework: Read pg. 1006-1008 (997-999); exoskeletons vs. endoskeletons Two major proteins and many minor proteins are involved in skeletal muscle: • Actin – alpha actin filament or thin filament • myosin o Made up of 6 subunits o Head converts ATP  ADP + P o Also called motor proteins • Alpha actinin – part of structure • Capping protein • Tropomyosin – long thing dimer; affinity for actin; binds actin filaments • Troponin complex – trimer (3 sub units); one will bind Ca, one will bind tropomyosin, other binds actin • Other proteins (dystrophin – structural role in muscle cells) All of these proteins work together to form skeletal muscles: refer to slide 44 for diagram ***I don’t think this cycle is correct***Refer to this instead: http://connect.mcgrawhill.c a/app/mod/resource/view.p hp?id=2715339 Cycle: 1. Myosin heads are charged (ADP + P from ATP) 2. Signal to contract (depolarization); Calcium stored in the ER is released, binding troponin complex to myosin. Conformational change. Tropomyosin is also bound to the troponin complex, which then lifted up to expose actin and allow binding 3. Sarcoplasmic reticulum 4. Myosin releases phosphate and bends (still attached to actin). The bending pulls actin filament; ATP is used 5. As conformation changes occur, ADP is lost (myosin can only hold two things: Homework: explain muscle contraction to a friend Rigormortis – stiffness of body after death (couple hours) • From step one, no ATP can be produced, therefore no contraction occurs • Refer to slide 46 for steak example i-clicker: Cystic fibrosis symptoms is… thick mucous Which has an ATP binding site… myosin has ATP binding site Homework: read about skeletal muscle structure pg 1009-1011 Skeletal muscle structure – the big picture • Muscle – grouping of cells (muscle fibers) bound together by connective tissue • Tendons link bones to skeletal muscle • Skeletal muscle fibers increase in size during growth but no new fibers are formed Three Major Types of Muscle Fibers • Slow-oxidative o Contains myosin with relatively low ATPase activity, but with numerous mitochondria o Prolonged, regular activity o “red muscles” • Fast-oxidative o Myosin has high ATPase activity and numerous mitochondria o Rapid actions o Ex. Tail of rattlesnake • Fast –glycolytic o Few myosin with high ATPase activity, but few mitochondria and relatively little available myoglobin (protein that delivers oxygen to muscle fibers), giving it pale color o Rapid, intense actions, but muscle fatigues quickly disuse atrophy – loss/deterioration of tissue (usually muscle) due to a disease or due to injury (therefore, lack of use) • video: Chris Hadfield had to go through intensive full-body training in space to keep his body in a healthy state. Still had to be wheeled in a wheel-chair when he returned to Earth Component s of Muscle • sarcolemma reticulum - endoplasmic reticulum in muscle fiber • sarcoplsm – muscle fiber cytoplasm • sarcolemma – muscle fiber membrane • mitochondria • nuclei (smooth or cardiac muscle fiber/cell= single nucleus, skeletal muscle = more than one nucleus because of cell division or cell fusion) Myoblasts • immature muscle cells • experiment: starve myoblast cells of serum needed to grow (give them serum-free medium). Not enough growth factors, so they differentiate instead of divide. When they differentiate, they fuse. Cannot divide once they fuse/cannot regenerate muscle • amphibians CAN use myoblasts as stem cells to • experiment/research: in vitro grown meat (sausage): o extract myoblast stem cells from pig o add growth serum to trick them into fusing o exercise fused muscles by temperature-sensitive equipment to build muscles o grind up new muscle tissue i-clicker: 1. How do actin and myosin molecules interact? a) globular myosin heads bind to actin filaments b) globular actin heads bind to myosin filaments c) myosin filaments have to bend to connect the myosin heads d) tropoin complexes cross links myosin and actin filaments e) calcium ions connect myosin and actin filaments 2. The striated appearance (looking like parallel lines) of skeletal muscles is due to a) the dark color of myosin b) the regular arrangements of myofibrils in the muscle fibers c) the dense array of microtubles d)the dense packing of ATP molecules e) presence of urea Neural Transmission and Nervous Control • Neurons – cells in the nervous system that send and receive electrical and chemicals signals to and from other neurons throughout the body • Animals have neurons except for sponges • Number of neurons varies widely as a function of size and behavioral complexity The Neuron • Nerves – contains hundreds of neurons • Dendrites (“tree”) – gets info from outside or another neuron • Cell body – contains nucleus • Ganglion – collection of neuron cell bodies • Axon - takes info away from cell body; vary in length depending on the organism • Nerve tract - bundle of axons • Myelin sheath – formed by by glial cells (“glue”) around neuron; acts as insulation • Glia – cells that produce connective tissue and myelin Types of Neurons • Sensory o gets info from outside world o Highly branched dendrites o Long axons • Motor o Send signals away from sensory neurons for a response (ex. muscle cell) o Long axon • Interneuron o Make interconnections with other neurons o Complex dendrite structure o Found in brain Homework: read 42.4 (pg 982 and 973-974: sensory receptors), look at figs and legends for ch 42 for a brief overview of reception types Voltage Sensitive Ion Channels • Permease – membrane proteins neurons and muscle cells have unique permease that are not found anywhere else: voltage gated ion channels (not a pump, no ATP) • Sodium channels – have activation and inactivation gate o -70mV difference between cytoplasm and extracellular fluid (higher conc’n outside) therefore membrane is polarized • Potassium channels – only have one gate • Greater conc’n inside cells • Normally outside membrane is more positive, but when stimulus causes a conformational change and the channels open (Na+ or positive charge goes in [current], causing the next channel to open up and more Na+ enters cell) until membrane becomes depolarized. • Accumulation of positive Na+ ions causes K+ voltage gated channel to open up and Na+ flows back outside • K+ closes a bit slower, meaning that a bit too much Na+ flows out (hyperpolarized), but eventually -70
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