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Fundamentals of Human Energy Transfer

Section 3: Energy Transfer. Fundamentals of Human Energy Transfer. Chapter 5. Fundamental Definitions. Bioenergetics studies diverse means for energy transfer for biologic work within living organisms.

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Fundamentals of Human Energy Transfer

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  1. Section 3: Energy Transfer Fundamentals of Human Energy Transfer Chapter 5

  2. Fundamental Definitions • Bioenergetics studies diverse means for energy transfer for biologic work within living organisms. • Aerobic and anaerobic breakdown of food nutrients provides energy for synthesizing the chemical fuel for all biologic work.

  3. Energy: The Capacity for Work

  4. First Law of Thermodynamics • Conservation of energy • Dictates that the body does not produce, consume, or use up energy; rather, energy transforms from one form into another as physiologic systems undergo continual change.

  5. Definition of Energy • Potential Energy: stored, inactive; ability to do work even if it is not doing work at the time. • Kinetic Energy: energy at work, active.

  6. Potential Energy as • Energy of position (gravitational) • Mechanical potential energy (elastic deformation) • Bound energy within internal structure Releasing potential energy transforms into kinetic energy of motion.

  7. 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

  8. Coupled Reactions

  9. Second Law of Thermodynamics • Tendency to degrade potential energy to kinetic energy with lower capacity for work (i.e., increase entropy). • Food and other chemicals represent excellent sources of potential energy, yet energy decreases as compounds decompose via normal oxidation. • Example: flashlight battery.

  10. Forms of Energy • During energy conversions, a loss of potential energy from one source often produces increase in potential energy of another source.

  11. Biologic Work in Humans Performance of mechanical work Chemical work in biosynthesis of macromolecules Active transport of molecules and ions concentrating various substances in & out of cells.

  12. 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

  13. Factors Affecting Bioenergetics • Enzymes • Reaction rates: operation rate of enzymes • Enzyme mode of action: how an enzyme reacts with its specific substrate • Coenzymes

  14. Enzymes • Are highly specific protein catalysts • Accelerate the forward and reverse reactions • Are neither consumed nor changed in the reaction • pH and temperature dramatically affect enzyme activity • Named for functions they perform “-ase”

  15. Reaction Rates • The rate of exergonic and endergonic reactions depends on: • Substrate availability • Enzyme availability • Metabolic state of the cell • Cellular conditions (temperature, pH) • Energy charge is maintained.

  16. Coenzymes • Complex nonprotein organic substances facilitate enzyme action by binding the substrate with its specific enzyme • Coenzymes are smaller molecules than enzymes • Many vitamins serve as coenzymes, e.g. riboflavin (flavin adenine dinucleotide) and niacin (nicotinamide adenine dinucleotide).

  17. Phosphate-Bond Energy

  18. ATP: The Energy Currency • Adenosine triphosphate provides the required energy for all cellular functions • Cell’s “energy currency” • ATP + H2O ↔ ADP + Pi + ∆ G (free energy) + heat • ATP hydrolysis yields 7.3 kcal of free energy.

  19. Structure of Adenosine Triphosphate (ATP)

  20. ATP  ADP Cycle is the fundamental mode of energy release in biological systems. Anabolic: use extracted chemical energy from ATP to synthesize new compounds. Catabolic: release energy for biologic work.

  21. Catabolism-Anabolism Interactions

  22. ATP-ADP Cycle Synthesized end products Carbohydrates, fats, proteins, and O2 ADP + Pi Anabolism (endergonic) Catabolism (exergonic) Building block precursors H2O + CO2 ATP

  23. How much ATP can the body store? Why do cells store small quantity?

  24. Phosphocreatine • Energy rich phosphate compound closely related to ATP. • Contains an energy rich phosphoanhydride bond. Insert Figure 3.7

  25. Released energy is coupled with energy requirement for re-synthesis of ATP. • For every mole of PCr broken down, 1 mole of ATP synthesized. • The coupled reaction is: Where is PCr stored?

  26. Intramuscular High Energy Phosphates • How long can high energy phosphates sustain all-out activity? • Mobilization of ATP and PCr important in determining anaerobic power.

  27. Cellular Oxidation Phosphorylation: the energy transfer through the phosphate bonds of ATP to other compounds to raise them to a higher activation level Oxidation: biologic burning of macronutrients in the body for the energy needed for phosphorylation Occurs on inner lining of mitochondrial membranes Involves transferring electrons from NADH and FADH2 to molecular oxygen, which release and transfer chemical energy to combine ATP from ADP plus a phosphate ion. During aerobic ATP resynthesis, oxygen combines with hydrogen to form water. More than 90% of ATP synthesis takes place in the respiratory chain by oxidative reactions coupled with phosphorylation.

  28. Cellular Oxidation • Human energy dynamics involve transferring energy by chemical bonds. • Energy for phosphorylation comes from oxidation of carbohydrate, lipid, and protein macronutrients.

  29. Cellular Oxidation • Oxidation reaction: an element loses electrons (e-); a compound loses electrons, often accompanied by hydrogen ions (H+), or it gains oxygen. • Reduction reaction: an element gains electrons (e-); a compound gains electrons, or it loses oxygen.

  30. Cellular Oxidation • Oxidation-reduction reactions are coupled. Every oxidation coincides with a reduction. • OILRIG: Oxidation Involves Loss Reduction Involves Gain • LEO the lion says GER: Lose Electrons Oxidation Gain Electrons Reduction

  31. Cellular Oxidation • Oxidation-reduction reactions are coupled. Every reduction coincides with a oxidation (redox). • Cellular oxidation-reduction constitutes mechanism for energy metabolism. • Carbohydrate, fat, and protein provide hydrogen atoms for this process.

  32. Cellular Oxidation • Hydrogens released from food molecules picked up by coenzyme NAD+ & sometimes FAD in cytosol. • Substrate oxidizes & loses hydrogens (electrons), NAD+ gains a hydrogen & 2 electrons and reduces to NADH, the other H+ in fluid • FAD also catalyzes dehydro-genations and accepts pairs of electrons.

  33. Cellular Oxidation • NADH and FADH2 formed in macronutrient breakdown in cytosol carry electrons to cytochromes in mitochondrial membrane. Animation: chemical rxns mitochondrion • Cytochromes, a series of iron-protein electron carriers, pass pairs of electrons in bucket brigade fashion on the inner membranes of mitochondrion.

  34. Cellular Oxidation Transport of electrons by specific carriers constitutes the respiratory chain or electron transport chain.

  35. Cellular Oxidation • The final electron acceptor (oxidizer) in the respiratory chain is oxygen which forms water. • Without oxygen as final oxidizer, respiratory chain cannot proceed and H remain in cellular cytosol.Animation: Electron Transport

  36. Oxidative Phosphorylation • Oxidative phosphorylation: refers to the phosphorylation of ADP during the electron transport from NADH and FADH2 to oxygen. • Electrochemical energy generated in the ETC is harnessed and transferred to ATP synthase which phosphorylates ADP to ATP.

  37. Energy Release from Food

  38. Carbohydrate Energy Release from Carbohydrate • What is the primary function of CHO? • The only macronutrient whose potential energy generates ATP anaerobically • During light & moderate intensity activity CHO supplies about ?????body’s needs. • A continual breakdown of CHO is required so lipid can be used for energy.

  39. Carbohydrate Energy Release from Carbohydrate • Compare rate of aerobic breakdown of CHO to lipid. • Net energy yield per molecule of glucose is ?? moles of ATP. • Of 689 kCal from one mole of glucose, only 38% (263 kCals) of the energy is conserved within ATP bonds; the remainder is dissipated as heat

  40. Glycolysis Carbohydrate Glycolysis: a series of 10 enzymatically controlled chemical reactions involving breakdown of glucose to two molecules of pyruvate. Anaerobic Glycolysis: breakdown of glucose to 2 lactates. Aerobic Glycolysis: breakdown of glucose to 2 pyruvates which then continue catabolism to acetyl coenzyme A.

  41. Carbohydrate • Glycolysis occurs in cell’s cytoplasm. • What is energy yield in glycolysis? • Energy from glycolysis is useful performing what exercise? • How many pairs of hydrogen are released during glycolysis?

  42. Carbohydrate Anaerobic Glycolysis Formation of lactic acid occurs when excess H from NADH temporarily combine with pyruvic acid.

  43. Carbohydrate Body disposes of lactic acid in two ways: • When sufficient O2 available within muscles, lactate returns H to pyruvic acid for aerobic metabolism. • Cori cycle in liver: gluconeogenesis – make glucose from lactate. Animation: Biochemical Cori Cycle

  44. Carbohydrate Stage Two of energy release from carbohydrate takes place in the mitochondrion. Two coenzyme A’s pick up the 2 two-carbon acetyl group and transport into mitochondria, releasing carbon dioxide molecules. Coenzyme A then releases the acetyl to begin TCA cycle.

  45. Carbohydrate

  46. Carbohydrate The citric acid cycle, or Kreb’s cycle, or tricarboxylate cycle is a series of 10 enzymatically controlled chemical reactions which begins with oxaloacetate and ends with oxaloacetate.Animation: citric acid cycle What is the most important function of the citric acid cycle? How many ATP are formed directly from substrates?

  47. Carbohydrate What is the net energy transfer from the complete catabolism of glucose?

  48. Fat 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

  49. Fat 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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