Nutrition, Metabolism, and Energy Notes

Energy Needs in Living Organisms

• All living organisms require energy for survival.
• Plants capture solar energy and convert it into stored chemical energy in biomolecules through photosynthesis.
• Key Processes:
  • Photosynthesis: Converts sunlight, carbon dioxide ($CO2$), and water ($H2O$) into glucose with oxygen ($O_2$) as a byproduct.
  • Respiration: Animals consume plants, using or storing the energy, releasing $CO2$ and $H2O$ while generating ATP.

ATP as Energy Currency

• ATP (Adenosine Triphosphate): The primary energy transfer molecule in biological systems.
• Phosphate bonds in ATP can be hydrolyzed to release energy in three types of work:
  • Transport Work: ATP phosphorylates transport proteins to move solutes across membranes.
  • Mechanical Work: ATP phosphorylates proteins in muscle cells allowing contraction.
  • Chemical Work: ATP drives endergonic reactions by donating phosphate to substrates.

Macronutrients and Their Functions

• Carbohydrates
  • Classification: Monosaccharides, disaccharides, polysaccharides.
  • Function: Energy source; glycogen as energy storage in liver/muscle.
• Lipids
  • Types: Triglycerides, steroids, phospholipids.
  • Function: Energy storage; structural components of membranes.
• Proteins
  • Composed of amino acids; essential for structure and function in cells.

Metabolism Overview

• Metabolism: Encompasses two major processes:
  • Catabolism: Breakdown of molecules to produce energy, converting complex into simple molecules (e.g., glucose).
  • Anabolism: Build complex molecules from simpler ones, consuming ATP.
• Energy Is Stored: In molecules like fat and glycogen, and utilized for growth and cellular functions.

Three Stages of Processing Energy-Containing Nutrients

1. Digestion: Break down food into absorbable forms; nutrients enter the bloodstream.
2. Anabolism & Catabolism: Nutrients are processed in cells. E.g., glycolysis, generates ATP from glucose.
3. Oxidative Breakdown: Occurs in mitochondria, involves electron transport and results in ATP production.

Cellular Respiration

• Overall Process: Glucose ($C6H{12}O6$) is oxidized to produce ATP, water, and $CO2$.
• Formula:
  C6H{12}O6 + 6O2
  ightarrow 6CO2 + 6H2O + ATP
• Phases:
  1. Glycolysis: Glucose is broken down into pyruvate; occurs in cytosol.
  2. Krebs Cycle: Pyruvate converted into carbon dioxide in mitochondria, generating NADH and FADH2.
  3. Electron Transport Chain: High-energy electrons facilitate the production of ATP through oxidative phosphorylation (up to 34 ATP produced).

Energy Production Pathways

• Aerobic vs. Anaerobic Pathways:
  • Aerobic: Efficient (36-38 ATP), requires oxygen; involves mitochondria.
  • Anaerobic: Inefficient (2 ATP), does not require oxygen; occurs in cytosol (e.g., lactic acid fermentation).

Fate of Glucose, Lipids, and Proteins

• Glucose Anabolism: Stored as glycogen (glycogenesis) or released into the bloodstream (glycogenolysis).
• Lipid Metabolism:
  • Beta oxidation converts fatty acids to Acetyl CoA for ATP production.
  • Lipogenesis synthesizes fats from excess Acetyl CoA.
• Protein Anabolism: Amino acids can be used for energy, structural proteins, and enzymes. Degradation involves transamination and deamination processes.

Key Takeaways

• ATP is essential for cellular energy transfer.
• Metabolic pathways determine how nutrients are converted to energy.
• The human body relies on a variety of biochemical pathways to derive energy from carbohydrates, fats, and proteins, adapting based on oxygen availability and exercise intensity.