BIOL 203 notes - Lecture 10 (Muscle I) -Thick filaments...

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Lecture 10 (Muscle I) -Thick filaments contain myosin -Think filaments contain actin -The segments are called sarcomeres -The junction of an axon with a muscle fiber is a specialized structure called the neuromuscular junction -Once the acetylcholine molecules bind to specific acetylcholine receptor molecules in the sarcolemma of the motor end plate. The result of this binding is a wave of electrical depolarization ( =action potential) that spreads over the sarcolemma and ultimately causes the muscle to contract. -The action of acetylcholine is brief because it is rapidly hydrolyzed by an enzyme called cholinesterase . [Neuromuscular Transmission Can Be Blocked by Drugs and Disease] - Curare is a poison that blocks neuromuscular transmission by binding to acetylcholine receptors. Then acetylcholine can’t bind to the receptors and leads to paralysis -The snake venom a-bungarotoxin acts similarly to curare - Botulinum toxin prevents the release of acetylcholine. Most potent toxins known -Black widow venom (latrotoxin)- explosive release of AcCh. [Excitation-Contraction Coupling] 1. The action of acetylcholine at the neuromuscular junction causes a wave of depolarization to spread of the sarcolemma 2. This wave causes the sarcoplasmic reticulum to release a large amount of calcium ions 3. The calcium ions then bind to troponin, which then causes a change in the tropomyosin molecule so that it no longer hinders the binding of myosin to actin, and the primed myosin molecule is free to attach to actin and generate the power stroke of muscle contraction. [Muscle Relaxation] - An ATP-driven pump, pumps the calcium ions out of the sarcoplasm to the sarcoplasmic reticulum, where much of it bind to a protein called calsequestrin . [Rigor Mortis]
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- When a person dies they can’t generate ATP and the calcium ions just keep leaking into the sarcoplasm keeping the muscles contracted [ATP and Creatine Phosphate] -During the start of a vigorous muscular contraction, ATP is hydrolyzed into ADP and P i . The amount of ATP in a muscle sometimes can’t fulfill the demand for an athlete. However, there is a pool of energy stored in the cell in the form of creatine phosphate . The enzyme creatine phosphokinase transfers the high-energy phosphate group of creatine phosphate to ADP, so generating more ATP for immediate use. This is known as Phosphagen System. [Oxygen Supply] -Creatine phosphate is the major source of energy during the first 8-10 seconds of a 100-meter sprint. After that time, The muscles depend on cellular metabolism as a source of energy for synthesizing more ATP. Muscle Metabolism -Glycolysis -Formation of acetyl CoA. -Krebs cycle -Oxidative phosphorylation - In most tissues, oxygen for oxidative phophorylation is provided by hemoglobin in the blood. However, some skeletal muscles and cardiac muscle contain a related re protein called
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This note was uploaded on 11/17/2010 for the course BIOL 333 taught by Professor Walter during the Spring '10 term at Purdue University.

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BIOL 203 notes - Lecture 10 (Muscle I) -Thick filaments...

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