Metabolism

Metabolism

Energy Metabolism

  • Obtaining and spending energy from food

Metabolic Reactions

  • Anabolic reactions:
      - Definition: Small molecules are used to build larger molecules.
      - Requires energy and is more prominent during growth.
      - Example: Building muscle cells with amino acids.

  • Catabolic reactions:
      - Definition: Large molecules are broken down into smaller molecules.
      - Releases energy and is more prominent during weight loss or wasting disease.
      - Example: Breaking down glycogen stores to yield glucose.

Summary of Reactions

  • Anabolic Reactions: Use energy

  • Catabolic Reactions: Produce energy

Adenosine Triphosphate (ATP)

  • Definition: A high-energy compound produced by metabolic reactions.

  • Function: ATP provides the energy that powers all cellular activities.

  • Energy Conversion: The body converts the energy from food to ATP with about 50% efficiency; the rest is lost as heat.

  • Recycling: A cell is constantly breaking down ATP for energy and then rebuilding it to maintain a steady energy supply for the body.

Structure of ATP

  • Components:
      - Adenine
      - Ribose
      - Phosphate groups
      - High-energy bonds

  • Energy Capture: ATP captures and stores energy in the bonds between its phosphate groups.

Vitamins & Minerals in ATP Production

  • Essential for roles in metabolic pathways:
      - Vitamins: Thiamin, Riboflavin, Niacin, Pantothenic acid, Vitamin B-6, Biotin, Folate, Vitamin B-12
      - Minerals: Iron, Copper

Breaking Down Nutrients for Energy

  • Digestion Yields:
      - Protein: Amino acids
      - Carbohydrate: Glucose
      - Fat: Glycerol and Fatty acids

Metabolic Pathways

  1. All energy-yielding nutrients (protein, carbohydrate, fat) can be broken down to acetyl CoA.

  2. Acetyl CoA can enter the TCA cycle.

  3. Most reactions release hydrogen atoms with their electrons, carried by coenzymes to the electron transport chain.

  4. ATP is synthesized.

  5. Hydrogen atoms react with oxygen to produce water.

Nutrient Energies

  • Fats: 9 kcal/gram
      - A 16-carbon fatty acid yields 106 ATP.

  • Carbohydrates: 4 kcal/gram
      - A glucose molecule yields 32 ATP.

  • Proteins: 4 kcal/gram
      - Priority is not energy.

Energy Balance / Weight Management

  • When energy intake exceeds energy output, weight gain occurs.
      - Excess energy sources: carbohydrate, protein, fat, or alcohol.
      - Efficient storage: Fat is the most efficient in being stored as fat.

Breakdown of Components

  1. Carbohydrate: When overeating, the body stores small glycogen amounts and larger amounts of fat.

  2. Fat: When fasting, glycogen and fat stores provide energy.

  3. Protein: When fasting continues beyond glycogen depletion, the body breaks down protein into amino acids for glucose needed by the brain and nervous system.
       - Result: Liver converts fats to ketone bodies as an alternative energy source.

Effects of Overeating / Undereating

  • Feasting:
      - Protein: Used for new cells, enzymes, antibodies, excess forms fatty acids.
      - Carbohydrates: Excess converted to glycogen, then to fat.
      - Fats: Efficiently converted to stored fat.
      - Conclusion: Consuming excess energy-yielding nutrients results in weight gain.

  • Fasting Adaptations:
      - Slows metabolic rate
      - Reduces energy requirements
      - Slows breakdown of lean body tissue for gluconeogenesis
      - Allows nervous system to utilize more ketone bodies.
      - Critical Condition: After losing 50% of lean body mass, death occurs.