Download Fundamentals of Human Energy Transfer

Section 3:
Energy Transfer
Fundamentals of Human
Energy Transfer
Chapter 5
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
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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
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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
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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”
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Energy: The Capacity for Work
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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
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Key Point
• 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
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Factors Affecting Bioenergetics
•
•
•
•
Enzymes
Reaction rates
Enzyme mode of action
Coenzymes
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Enzymes
• Are highly specific protein catalysts
• Accelerate the forward and reverse
reactions
• Are neither consumed nor changed in
the reaction
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Coenzymes
• Complex nonprotein organic substances
facilitate enzyme action by binding the
substrate with its specific enzyme
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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
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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
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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 2carbon 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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