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Force of Contraction Number of fibers and stimuli Temporal summation and recruitment of fibers Size of muscle--larger muscle, larger force Elastic Elements -Non-contractile elements of muscle cells 1) Connective tissue 2) Tendons 3) Organelles 4) Sarcolemma Supporting proteins 1) Titin 2) Nebulin Tension Overcome elasticity a. Internal tension—overcome noncontractile elements b. External tension--overcome actual load Velocity and Duration of Contraction -Size of load determines velocity of shortening Energy for Muscle Contraction A. Metabolism--all biochemical events 1. Anabolism--build up 2. Catabolism--break down 3. Cellular (internal) Respiration--generate ATP 4. Metabolic Flow--from beginning to end Process of taking energy in ! utilizing it to build structural and functional products and ATP ! removing waste Substrate Phosphorylation --Typically see with formation of ATP (Direct phosphorylation) X䍐P + ADP ! X + ATP Cofactors: NAD+ FAD+ Oxidative Phosphorylation Mitochondrion--electron transport chain--multistep process; involves oxygen (Indirect phosphorylation) Mechanisms of ATP Synthesis 1. Anaerobic Sources of ATP a. Stored ATP--myosin head (pre-synthesized) ATP b. Creatine kinase Creatine䍐P + ADP ! ATP + Creatine Quickest sources of energy Glycolysis--glucose breakdown Yields the following from 1 molecule of glucose: 1) 2 pyruvates (pyruvic acid) 2) a net of 2 ATP (immediate energy)** 3) 2 forms of NAD+! Pathway of Glycolosis--enzymes in cytoplasm of cell a) sugar activation--invest 2 ATP convert glucose to fructose F-1,6-P This molecule is “energized” b) Sugar cleavage Break 6-carbon molecule into 2, 3-carbon molecules, each carrying phosphate DHAP G-3-P c) Oxidation and ATP formation C molecule is oxidized: H atoms removed and transferred to NAD (NADH + H+) 4 ADP are phosphorylated to ATP (net +2 ATP) Glycolysis Continue Later Aerobic Respiration Mitochondrial--3 processes: 1) Conversion of pyruvate to Acetyl CoA (2 molecules) 3C pyruvate ! 2C (acetyl CoA); Release CO2 generate NADH +H+ ; 2) Krebs Cycle Acetyl CoA (2C) broken down completely to yield: 3 NADH + H+ x 2 1 FADH2, x 2 1 ATP x 2 Glucose was split in half during glycolysis. Two “turns” of the Krebs cycle per glucose molecule. CO2 is waste Mitochondrial matrix Enzymes at each step 3)! Electron Transport Chain --extracts energy from reduced compounds and synthesizes ATP Splits H atom into proton and e- Uses O2!!! Summary of Energy Produced Muscle Work 1. Energy Production a. Anaerobic--does not require O2 b. Aerobic--requires O2 Anaerobic Threshold--during heavy exercise, an increase in blood lactate is seen. Interpreted to mean that body was converting from aerobic (Krebs, etc) to anaerobic (glycolysis) mechanisms for ATP synthesis due to lack of oxygen in mitochondrion. This definition is untrue. Oxygen is present in the mitochondrion. Krebs and e.t.c enzymes have collectively slower velocity than the glycolysis enzymes. During exercise, lactate builds up. Lactate is not a waste product, it is also a fuel. wrong Fatigue a. Definition--ATP production fails to keep pace with usage psychological factors, pH, neurological transmission of action potential, mitochondrial function (chronic fatigue syndrome)