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

Copyright © 2006 Lippincott Williams & Wilkins.

Fundamentals of Human Energy Transfer

Chapter 5

Section 3: Energy Transfer


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


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


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


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”


Energy: The Capacity for Work


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




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




Examples of Biologic Work• Mechanical work

– Muscle contraction• Chemical work

– Synthesis of macromolecules• Transport work

– Concentration of various substances in intracellular and extracellular fluids


• 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


Factors Affecting Bioenergetics

• Enzymes • Reaction rates• Enzyme mode of action• Coenzymes


Enzymes• Are highly specific protein

catalysts• Accelerate the forward and reverse

reactions• Are neither consumed nor changed

in the reaction


Coenzymes • Complex nonprotein organic

substances facilitate enzyme action by binding the substrate with its specific enzyme


Phosphate-Bond Energy










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










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


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


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




Did You Know?• As carbohydrate levels decrease,

the availability of oxaloacetate may become inadequate, which impairs fat catabolism




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