022509 Section 07

022509 Section 07 - Patrick Corpuz [email protected] A01 Mon...

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Patrick Corpuz [email protected] A01: Mon. 8-8:50 Center 207 02/23/09 OH: Fri. 8-8:50 Leichtag Lobby A04: Wed. 8-8:50 Center 220 WEEK 7 I. Muscle A. Skeletal muscle – muscle usually attached to the bone via tendons and is responsible for movement of the skeleton (voluntary movement) 1. Structure (Fig. 12.3) a. Skeletal muscle is made up of bundles of muscle fibers , and each muscle fiber is made up of myofibrils b. Muscle fibers – individual muscle cells that contain several nuclei i. The sarcolemma , or cell membrane, of the muscle fibers has invaginations called t-tubules . c. Myofibrils – the main intracellular structure of the muscle fiber i. Each myofibril is made up of sarcomeres – the basic unit of contraction ii. Each myofibril contains a “sac”, called the sarcoplasmic reticulum, which collects and stores Ca++ 2. The sarcomere a. A sarcomere is made up of thick and thin filaments i. Thick filaments = myosin ii. Thin filaments = actin b. The thick and thin filaments are connected by crossbridges – the myosin heads that loosely bind to the actin filaments c. The thin filaments are “wrapped” in tropomyosin which in turn is regulated by troponin 3. Actin-myosin contraction a. The sliding-filament theory of contraction: i. States that the overlapping thick and thin filaments are of fixed length, that is their length remains unchanged during a contraction ii. the reason the sarcomere shortening: filaments are sliding past one another (Fig 12.7) b. What causes the sliding movement? i. The power stroke of the myosin crossbridges – movement of the myosin heads pushes the thin actin filaments toward the center of the sarcomere c. What causes the movement of the myosin heads? i. Energy (ATP) – each myosin molecule is an ATPase that binds ATP and hydrolyzes it to ADP and Pi , this in turn releases energy which is then used to create the power stroke ii. Rigor State 1. Myosin heads are tightly bound to the actin filament and no ATP is present in the second binding site on the myosin head. 2. Occurs for only a brief period in living tissue 3. If tissue is dead, no ATP is present and the rigor state will give rise to rigor mortis as the myosin heads will not release the actin iii. ATP Binds and Myosin Releases Actin 1. The binding of ATP to the other site on the myosin head changes its affinity for actin and the head releases. iv. ATP Hydrolysis 1. Hydrolysis of ATP to ADP and inorganic phosphate which
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Patrick Corpuz [email protected] A01: Mon. 8-8:50 Center 207 02/23/09 OH: Fri. 8-8:50 Leichtag Lobby A04: Wed. 8-8:50 Center 220 remains bound to myosin. v. Myosin Reattaches To Actin 1. ATP energy rotates the myosin which now binds at a position further away on the actin molecule. 2.
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022509 Section 07 - Patrick Corpuz [email protected] A01 Mon...

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