1. Fundamentals of Human Energy Transfer
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. Releasing potential energy transforms into kinetic energy of motion.
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.

17. 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).

18. Phosphate-Bond Energy

19. 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.

20. Structure of Adenosine Triphosphate (ATP)

21. 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.

22. Catabolism-Anabolism Interactions

23. Carbohydrates, fats, proteins, and O2
ATP-ADP Cycle
Synthesized
end products
Carbohydrates, fats, proteins, and O2
ADP + Pi
Anabolism
(endergonic)
Catabolism
(exergonic)
Because energy from ATP hydrolysis powers all forms of biologic work, ATP constitutes the cell’s energy currency.
Building block
precursors
ATP
H2O + CO2

24. How much ATP can the body store?
3.5 ounces ( g). Ratio of ADP:ATP provides sensitive mechanism for regulating energy metabolism in cell. Crucial feedback for rapid formation of ATP from high energy phosphates.
How much ATP can the body store?
Why do cells store small quantity?

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

26. 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?

27. Intramuscular High Energy Phosphates
How long can high energy phosphates sustain all-out activity?
Mobilization of ATP and PCr important in determining anaerobic power.
Activities such as sprinting, jumping, throwing for approximately 5 to 8 seconds.

28. 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.

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

30. 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.

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

32. 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.

33. 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.

34. 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.

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

36. 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

37. 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.

38. Energy Release from Food

39. 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.
CHO supplies about half body’s needs.

40. 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
Aerobic breakdown of CHO occurs at twice rate from fatty acid.

41. 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.

42. 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?

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

44. Body disposes of lactic acid in two ways:
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

45. 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.

46. Carbohydrate

47. 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?
To remove H for transport to respiratory chain.
2 for each glucose (1 for each pyruvate)

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

49. 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

50. 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

51. Breakdown of Glycerol and Fatty Acids
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

52. Fat
Fuel reserves from fat represents about 60,000 to 100,000 kcals in fat cells and 30,000 in intramuscular triglycerides. Carbohydrate reserves is <2,000 kcal.
Before energy release from fat: lypolysis.
FA diffuse from adipocyte into blood, bind to albumin & delivered to tissues.

53. Fat
Beta Oxidation

54. Fat
Did You Know?
As carbohydrate levels decrease, the availability of oxaloacetate may become inadequate, which impairs fat catabolism.
Fats burn in a carbohydrate flame.

55. Excess macronutrients convert to fat.
Any excess carbohydrate, lipid, or protein readily converted to fatty acid.

56. Energy Release from Protein
Protein can be used as energy substrate during endurance-type exercise.
To provide energy a.a. must be converted to usable form.

57. Metabolic Mill
Each pathway has rate-limiting enzyme.
Cellular [ADP] is most important factor that affects enzymes controlling energy metabolism.
Molecules degraded to few simple units, mostly acetyl CoA.
Notice reversibility except pyruvic acid to acetyl CoA.