1.10

• ATP


  High-energy phosphate compound
• ATP-ADP cycling


  1. Conversion of ATP to ADP + Pi powers life processes

  2. Conversion of Pi + ADP to ATP regenerates energy expended in cell operation
• ATP hydrolysis produces an intermediate amount of free energy (7.5 kcal/mol)
• ATP hydrolysis energy is a biochemically useful amount of energy
• ATP synthesis requires an energy input equal to or greater than the hydrolysis energy
• ATP molecules in cells have a high turnover rate, normally less than a minute before conversion to ADP
• Typical ATP concentration in a cell is 0.5 to 2.5 mg/mL of cellular fluid
• Older biochemistry textbooks stated NADH produces 3 ATP and FADH2 produces 2 ATP in the ETC, but this has been revised as the process is more complex
• More than 90% of oxygen taken into the human body is consumed by the electron transport chain/oxidative phosphorylation phase of metabolism
• Remaining oxygen is converted into reactive oxygen species (ROS) like hydrogen peroxide, superoxide ion, and hydroxyl radical
• Elimination of superoxide ion

  1. Superoxide dismutase converts superoxide ion to hydrogen peroxide

  2. Catalase converts hydrogen peroxide to water and oxygen
• Hydroxyl radicals can cause oxidative damage by reacting with and breaking bonds in lipids in cell membranes
• An estimated 5% of ROS escape normal destruction channels
• Antioxidant network


  • Includes glutathione, vitamin C, beta-carotene, vitamin E, and flavonoids
  • Prevents oxidative damage by reacting with harmful ROS before they can react with other biological substances
• Vitamin C is particularly active against free-radical damage from external influences like pollution, smoke, and radiation
• Antioxidant molecules provide electrons to convert free radicals and other ROS into less-reactive substances