Motor mechanisms II Review questions Binding of ATP to myosin head causes: • a) actin filament to slide What will happen when ADP and • b) Myosin head to detatch from actin Pi dissociate from myosin head? filament • A) head will detatch from actin filament • C) Myosin head to cock • B) head will retract and pull actin filament • C) head will bind ADP again Ca ++ induces muscle contraction by: • A) Causing actin monomers to assemble into a filament • B) making ATP available to bind to myosin head • C) allowing myosin head to bind to actin filament 1 Muscle fiber types are the result of different types (isoforms) of myosin • Type I - slow fibers (aerobic) • Type II - fast fibers (anaerobic) – Type IIx - very fast – Type IIa - intermediate between II x and I – Types present in other vertebrates, not humans • Quadriceps muscle stained for ATPase e.g., IIb in rats and other small mammals activity. Dark = type II fast; light = type I slow. • Type I slow twitch • Type II fast twitch – Slow contraction time – Fast contraction (50 (100 msec) msec) – Myoglobin (red) – No myoglobin (white) – Continuous use – Brief use – More capillaries – Few capillaries – Small size – Larger size • Type I and II stained for mitochondria. – Low glycogen – High glycogen Type I has dense mitochondria since it is – Low fat aerobic – High fat – More mitochondria – Few mitochondria 2 Characteristics of other muscle 1 types: Muscle cell • Cardiac muscle - found only in the heart, types striated, gap junctions allow direct electrical 2 signaling between cells schematic: • Smooth muscle - involuntary muscle, 1) skeletal meshwork of actin and myosin, can contract 2) cardiac more (greater shortening), but with less 3 tension. 3) smooth Skeletal muscle Cardiac muscle http://www.youtube .com/watch?v=Cdl8 Awn_lDY&feature =related http://www.youtube .com/watch?v=b1W D564sjWw&feature =related Smooth muscle 3.