SR1002 - Lecture 2.2 2022

Overview of Energy in the Body

Part 1: Energy Supply for the Body

Nutrient Sources

  • Different nutrients used for metabolism:

    • Carbohydrates: 16 kJ/g

    • Fat: 37 kJ/g

    • Protein: 17 kJ/g

    • Carbohydrates metabolized both aerobically and anaerobically

    • Proteins and fats require oxygen for metabolism

Energy Storage

  • Energy Sources:

    • Obtained from dietary intake

    • Stored energy for starvation:

      • Fat: 79%

      • Protein: 20%

      • Carbohydrates: 1%

    • Most energy used comes from carbohydrates (CHO)

Cellular Oxidation

  • Overview:

    • Biochemical mechanism underlying energy metabolism

    • Oxidation reactions, similar to combustions:

      • C6H12O6 + 6O2 → 6 CO2 + 6 H2O (aerobic glycolysis)

  • Controlled Enzymatic Reactions:

    • Convert and transfer chemical energy for metabolism

    • Energy is released in small portions

Electron Transport

  • Mechanisms:

    • Cellular redox reactions are key for energy metabolism.

    • NAD and FAD oxidize nutrients.

    • Carrier molecules transport electrons to redox complexes.

    • Oxygen as final electron acceptor, synthesizing ATP.

Reduction Equivalents

  • Energy currency:

    • NAD+, FAD: transport electrons from nutrients to oxygen.

    • NADH + H+ and FADH2 are crucial for redox reactions.

Oxidative Phosphorylation

  • Process:

    • Synthesizes ATP by transferring electrons from NADH and FADH2 to oxygen.

    • Involves high proton pumping and ATP resynthesis through a series of enzymatic reactions.

Part 2: Metabolism

Catabolic and Anabolic Metabolism

  • Definitions:

    • Catabolic metabolism: Breaks down nutrients, releases energy, creates metabolic intermediates.

    • Anabolic metabolism: Synthesizes new compounds (e.g., enzymes, fats, hormones), consumes energy.

    • Energy from catabolism fuels anabolism.

Phosphate Bond Energy

  • Adenosine Triphosphate (ATP):

    • Primary energy currency of cells, powers cellular processes.

    • Energy extracted from food and stored in ATP bonds.

ATP Hydrolysis

  • Mechanism:

    • Hydrolysis of ATP releases energy (~30.5 kJ/mol).

    • Enzyme ATPase catalyzes the reaction.

    • ATP used for mechanical work, transport, and synthesis.

Energy Productions and Applications

Mechanical Energy

  • Muscle Contraction:

    • Actin and myosin interactions involve ATP hydrolysis for movement.

Transport Work

  • Cellular Transport:

    • ATP powered transport of vesicles, ions, and metabolites across membranes.

Electrical Work

  • Neural and Muscle Activity:

    • Energy required for maintaining membrane potentials and conducting signals.

Heat Production

  • By-Products:

    • Every energy conversion releases heat as a by-product.

    • High heat generation during muscular activity and biochemical reactions.

Conclusion

  • Nutrients (carbohydrates, fats, proteins) generate metabolic energy via oxidation.

  • Energy is utilized to produce ATP, the body’s energy currency.

  • Importance of NAD and FAD as electron carriers in energy utilization.

  • ATP is critical for various cell functions, generating mechanical, transport, and chemical work, as well as producing waste heat.