Metabolism

Overview of Metabolism and Nutrition

  • Metabolism: Sum of body’s chemical reactions, includes enzyme-catalyzed reactions to harness energy from nutrients, synthesize macromolecules, and break down molecules.

  • Energy Measurement:

    • Calorie (C): Heat to raise one gram of water by 1°C.

    • Kilocalorie: Heat to raise one kg of water by 1°C.

Phases of Metabolism

  • Catabolism: Breakdown of substances to release energy (ATP generation).

    • Nutrient types:

    • Glucose: Preferred by many cells (brain, liver).

    • Fatty Acids: Breakdown into glycerol and free fatty acids.

    • Amino Acids: Derived from protein breakdown.

  • Anabolism: Combines smaller molecules into larger macromolecules (e.g., proteins, nucleic acids).

Energy Requirements

  • Exergonic Reactions: Release energy (most catabolic reactions).

  • Endergonic Reactions: Require energy input (most anabolic reactions).

  • Energy Coupling: Law of conservation of energy; energy from exergonic reactions fuels endergonic processes.

Adenosine Triphosphate (ATP)

  • ATP: Primary energy currency of the cell, inherently unstable due to negatively charged phosphate groups.

  • Hydrolysis: Breaking ATP releases energy; about 40% of energy harnessed for work.

  • Phosphorylation: Process where ATP donates a phosphate group to a reactant, increasing reactivity.

Electron Transport and ATP Generation

  • Oxidation-Reduction Reactions: Transfer electrons during catabolism to fuel ATP synthesis via electron carriers (NAD, FAD).

  • ATP Production from Nutrients:

    • Glucose catabolism: Involves glycolysis, citric acid cycle, and oxidative phosphorylation.

    • Glycolysis: Occurs in cytosol, breaks glucose into pyruvate.

Glucose and ATP Synthesis

  • Glycolysis: Net yield of 2 ATP and 2 NADH per glucose.

  • Citric Acid Cycle: Converts acetyl-CoA into NADH, FADH2, and ATP; operates twice per glucose molecule.

  • Electron Transport Chain: Final ATP production stage, employs electron carriers to generate ATP through oxidative phosphorylation.

Fatty Acid and Amino Acid Catabolism

  • Fatty Acid Breakdown: Triglycerides yield fatty acids and glycerol; oxidation occurs primarily in mitochondria.

  • Amino Acid Breakdown: Deamination removes amino groups; carbon skeletons converted into energy substrates.

Anabolic Pathways

  • Glycogenesis and Gluconeogenesis: Convert excess glucose to glycogen and synthesize glucose from non-carbohydrate sources, respectively.

  • Lipid Synthesis: Fatty acids synthesized via lipogenesis; critical for energy storage.

Metabolic States

  • Absorptive State: Nutrient absorption post-meal; promotes anabolism.

  • Postabsorptive State: Nutrient absorption complete; catabolism predominates for energy supply.

Nutrition and Body Mass

  • Nutrients: Include macronutrients (carbohydrates, proteins, lipids) and micronutrients (vitamins, minerals).

  • Healthy Diet Guidelines: Emphasis on balanced intake of nutrients, as per MyPlate recommendations.

  • Obesity Impact: Higher BMI linked to increased disease risk.