ETC and Oxidative Phosphorylation

• Mitochondria are regarded as the engine of the cell since most of the energy needed for cellular activity comes from them
• Citric acid cycle

  Second step of cellular respiration, generates two ATP per pyruvate molecule, and produces NADH and FADH2 for the electron transport chain
• Oxidative phosphorylation

  1. Generates the most ATP out of the pathways in cellular respiration

  2. Utilizes an electron transport chain with protein complexes I-IV

  3. Involves a series of redox reactions to shuttle electrons downhill

  4. Generates a proton gradient across the membrane

  5. Involves chemiosmosis where protons move through ATP synthase to generate ATP
• Glycolysis

  First step of cellular respiration, produces two ATP per glucose molecule
• Pyruvate from glycolysis and citric acid cycle


  Can enter the electron transport chain for ATP generation
• With NADH and FADH2 from a single molecule of glucose, around 26-28 ATPs can be generated through oxidative phosphorylation
• All food eventually gets broken down into compounds that are fed into the pathways of cellular respiration
• Trillions of enzymes in mitochondria help generate energy for cellular activities
• NADH and FADH2 from the citric acid cycle move on to oxidative phosphorylation to generate the most ATP
• Proton gradient is generated across the membrane in oxidative phosphorylation
• Oxidative phosphorylation

  1. Generates the most ATP out of the pathways in cellular respiration

  2. Utilizes an electron transport chain with protein complexes I-IV in the inner mitochondrial membrane

  3. Involves redox reactions to shuttle electrons downhill from one component to another

  4. Generates a proton gradient across the membrane

  5. Involves ATP synthase in synthesizing ATP through chemiosmosis and the proton-motive force
• ATP synthase


  • Component that synthesizes ATP
  • Powered by the proton-motive force in phosphorylating ADP to generate ATP
  • Has a rotor-like structure where protons bind and cause it to spin, catalyzing phosphorylation of ADP
• Chemiosmosis


  Protons accumulate outside the inner mitochondrial membrane and re-enter through ATP synthase, powering ATP synthesis
• Electron transport chain

  • Series of mitochondrial membrane proteins in the inner membrane of the mitochondrion
  • Protein complexes I-IV
  • Contain prosthetic groups like flavin mononucleotides and cytochromes
  • Includes ubiquinone (coenzyme Q) as a small hydrophobic molecule
• 26-28 ATPs can be generated from NADH and FADH2 from a single molecule of glucose in oxidative phosphorylation
• Mitochondria are regarded as the engine of the cell, providing most of the energy needed for cellular activity
• Glycolysis produces two ATPs per glucose and generates pyruvate, which enters the citric acid cycle to generate more ATP and NADH/FADH2 for the electron transport chain
• Other sources of food like proteins, fats, and carbohydrates are broken down into compounds that eventually feed into the pathways of cellular respiration
• All the food we eat eventually gets broken down through the pathways of cellular respiration