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Biological Sciences
Peter A.Bowler

e109 12/5/12 Fig 22.2 -Stored fat contains more kcal/g than glycogen (so more compact) -fat is 9 kcal/g; glycogen+ H20 is 1 kcal/g -Stored fat is mobilized (convert to ATP) more slowly than glycogen (as source ofATP) Energy content Gasoline (fossil fuel—that you put in your car): 44.4 MJ/kg =44.4 kJ/g x 1 kcal/4.2 kJ =10.6 kcal/g -Fat (adipose tissue) 9 kcal/g Remember that 1 kcal = 1 Calorie (used in nutrition) Exercise Ch. 25 -Integrated response from multiple body systems Exercise—start with muscle contraction -Skeletal muscle is the largest single tissue type in the human body >640 muscles ~30-40% of total body weight can be skeletal muscles ~25% of energy consumed by body at rest is used up by our muscles (they always have some level of tone/contraction) -transfer of Ca2+ back into sarcoplasmic reticulum -Our muscle cells do contain ATPand Phosphocreatine (PCr) (can transfer phosphate group to ATP)—powers 15 sec of exercise -Need to make moreATP-glycolysis (anaerobic), oxidative phosphorylation, and citric acid cycle (both aerobic) 1. Glucose absorbed at the intestine. Glucose travels through the blood to the muscle fiber. 2. In the muscle fiber, glycogen is converted to pyruvate then acetyl coAto turn intoATP 3. Glycerol + fatty acids lipids stored in adipose tissue In adipose tissue -What if not enough oxygen at muscle cell? Switch to anaerobic pathways (cannot be sustained for long periods of time—only 1 minute) 1. Glucose comes from liver glycogen or dietary intake (absorbed at the intestine) and enter the muscle cells 2. Fatty acids can only be used in aerobic metabolism and enter the muscle cells (Fatty- acids to acetyl coAis the slow step) 3. Lactic acid from anaerobic metabolism can be converted to glucose by liver. -Muscular contraction stimulates translocation of insulin-independent GLUT transporters to membrane -Hormonal changes during exercise:: insulin levels go down (decrease), and glycogen levels go up (increase); insulin is a hormone that helps uptake of glucose Speed ofATP production vs. endurance Fig 25-2 -Moles of ATP produced/min ::: Phosphocreatine (much higher at this level) can only sustain 10 seconds of maximal exercise -Anaerobic metabolism producesATP 2.5 times faster than aerobic metabolism but can only support 1 minute of maximal exercise -Aerobic metabolism supports exercise for hours (higher for endurance time for maximal muscle activity!)---fat burning How about exercise intensity? Fat mobilization is slow Percent substrate used by muscle vs. Exercise intension (% maximum) CHO= carbohydrates such as glycogen -At rest, about 60% of the calories are coming from fat and 40% of the calories are coming from glycogen like carbohydrates -As exercise intensity increases (sprinting), you burn fats not carbohydrates; at 100% maximum exercise intensity, you are burning glycogen because all the fat has been burned up already Fatty acids acetyl coA fat mobilization is slow If someone is interested in losing weight, is it better to exercise in the “fat-burning” or the “carbohydrate-burning” level of effort Energy in (calories) = energy out (calories burned) + energy stored (fat and glycogen) -Energy stored = the difference between energy in and energy out -muscle is an expensive tissue to maintain ; fat tissue has a very low cost to maintain Exercise type affects muscle fiber types -Slow-twitch oxidative muscle fibers: associated with aerobic metabolism, fatigue resistant, burns oxygen slower to makeATP, more capillary density, more mitochondria -Fast-twitch glycolytic muscles: associated with anaerobic metabolism, burnATP faster, burn out faster (easily fatigued) Lack of exercise affects muscle mass Weight-bearing activities: ~1/3 of skeletal muscle in immobilized limb can disappear within weeks (only the number of muscle cells change, not the number of muscle fibers) -Muscle atrophy is a problem for astronauts b/c they’re in space and do not perform weight- bearing activities b/c there is no gravity in space Protein breakdown Muscle glycogen can be used for energy. Muscles also u
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