Lecture IX

• Myofibrils are organelles for muscle fibers only
• Myofibrils, large tube for proteins
• Myofibrils, covered by sarcoplasmic reticulum
• T tubules are transverse tubules
• T tubules are an extension of the sarcolemma
• T tubules are where excitation reaches entire muscle fiber
• Sarcoplasmic reticulum wraps around myofibrils
• Sarcoplasmic reticulum contains calcium
• Sarcoplasmic reticulum interacts with T tubules
• Triad is two terminal cisternae and one t tubule
• Cisternae is a sac of water
• The triad is the key to excitation-contraction coupling
• Myofibrils have multiple sarcomeres
• Sarcomere are a functional unit of contraction, HAS to be there for contraction
• Sarcomere are how contractile and regulatory proteins are organized
• Sarcomere cause striation
• Thick filaments are intracellular
• Intracellular: inside cell
• Myosin: enzymatic function
• Myosin ATPase: hydrolyzes ATP
• Center of sarcomere, held in place by M line
• Entire length of myosin creates A band
• A band doesn't change
• Myosin only areas in H band
• H band gets smaller with contraction
• Zone of overlap is partially due to myosin, where actin and myosin are near
• Zone of overlap gets larger with contraction
• Thin filament. Actin is pulled and pushed by myosin
• Thin filament. Covered by tropomyosin: blocks actin's active site for myosin
• Thin filament. Troponin holds tropomyosin in place
• Thin filament. Calcium binds to troponin
• Thin filament. Actin found in I bands, at the end of the sarcomere
• Thin filament. I band gets smaller during contraction because the zone of overlap gets larger
• M Line anchors myosin
• M line does not change
• H band has myosin only
• H band shrinks with contraction
• Zone of Overlap. Lateral edges are defined by myosin
• Zone of Overlap. Myosin defines A band
• Zone of Overlap. Actin always with troponin and tropomyosin