Copyright © 2006 Lippincott Williams & Wilkins. Fundamentals of Human Energy Transfer Chapter 5 Section 3: Energy Transfer

Copyright © 2006 Lippincott Williams & Wilkins. Objectives Describe the first law of thermodynamics related to energy balance and biologic work Define the terms potential energy and kinetic energy and give examples of each Give examples of exergonic and endergonic chemical processes within the body and indicate their importance State the second law of thermodynamics and give a practical application

Copyright © 2006 Lippincott Williams & Wilkins. Objectives (cont’d) Identify and give examples of three forms of biologic work Discuss the role of enzymes and coenzymes in bioenergetics Identify the high-energy phosphates and discuss their contributions in powering biologic work

Copyright © 2006 Lippincott Williams & Wilkins. Objectives (cont’d) Outline the process of electron transport- oxidative phosphorylation Explain oxygen’s role in energy metabolism Describe how anaerobic energy release occurs in cells Describe lactate formation during progressively increasing exercise intensity

Copyright © 2006 Lippincott Williams & Wilkins. Objectives (cont’d) Outline the general pathways of the citric cycle during macronutrient catabolism Contrast ATP yield from carbohydrates, fats, and protein catabolism Explain the statement, “Fats burn in a carbohydrate flame”

Copyright © 2006 Lippincott Williams & Wilkins. Energy: The Capacity for Work

Copyright © 2006 Lippincott Williams & Wilkins. First Law of Thermodynamics Conservation of energy Dictates that the body does not produce, consume, or use up energy; rather, it transforms it from one form into another as physiologic systems undergo continual change

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Energy-Releasing and Energy-Conserving Processes Exergonic reactions –Chemical processes that release energy to its surroundings –Downhill processes Endergonic reactions –Chemical processes that store or absorb energy –Uphill processes

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Examples of Biologic Work Mechanical work –Muscle contraction Chemical work –Synthesis of macromolecules Transport work –Concentration of various substances in intracellular and extracellular fluids

Copyright © 2006 Lippincott Williams & Wilkins. The limits of exercise intensity ultimately depend on the rate that cells, extract, conserve, and transfer chemical energy in the food nutrients to the contractile filaments of skeletal muscle Key Point

Copyright © 2006 Lippincott Williams & Wilkins. Factors Affecting Bioenergetics Enzymes Reaction rates Enzyme mode of action Coenzymes

Copyright © 2006 Lippincott Williams & Wilkins. Enzymes Are highly specific protein catalysts Accelerate the forward and reverse reactions Are neither consumed nor changed in the reaction

Copyright © 2006 Lippincott Williams & Wilkins. Coenzymes Complex nonprotein organic substances facilitate enzyme action by binding the substrate with its specific enzyme

Copyright © 2006 Lippincott Williams & Wilkins. Phosphate-Bond Energy

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Energy Release from Carbohydrate The only macronutrient whose potential energy generates ATP anaerobically The complete breakdown of 1 mole of glucose liberates ~689 kCal of energy Of which, only 38% (263 kCals) of the energy is conserved within ATP bonds; the remainder is dissipated as heat

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Energy Release from Fat Adipocytes –Site of fat storage and mobilization –95% of an adipocyte’s volume is occupied by triacylglycerol (TG) fat droplets –Lipolysis splits TG molecules into glycerol and three water-soluble free fatty acids (FFA) –Catalyzed by hormone-sensitive lipase

Copyright © 2006 Lippincott Williams & Wilkins. Transport and Uptake of Free Fatty Acids After diffusing into the circulation, FFA are transported within the circulation bound to albumin FFA are then taken up by active skeletal muscle in proportion to their flow and concentration

Copyright © 2006 Lippincott Williams & Wilkins. Breakdown of Glycerol and Fatty Acids Glycerol –Is converted to 3-phosphoglyceraldehyde, an intermediate glycolytic metabolite FFA –Are transformed into acetyl–CoA in the mitochondria during  -oxidation –A process that successively releases 2- carbon acetyl fragments split from long fatty acid chains

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Did You Know? As carbohydrate levels decrease, the availability of oxaloacetate may become inadequate, which impairs fat catabolism

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