Metabolism and ATP Synthesis Notes

Metabolism

• Metabolism: Biochemical processes (reactions) within cells to maintain life.

• Two types of reactions:

  • Anabolism: Synthesis of large molecules from small ones.

    • Example: Amino acids > proteins

    • Example: Glucose > glycogen

  • Catabolism: Hydrolysis of complex structures to simple ones.

    • Example: Proteins > Amino acids

    • Example: Glucose > CO₂ + H₂O

• Cellular respiration:

  • Occurs in the mitochondria.

  • Catabolism of food to form ATP for cells (anabolism).

  • Equation: C₆H₁₂O₆ + 6O₂ > 6CO₂ + 6H₂O (Catabolic), ADP + Pi > ATP (anabolic)

  • ATP is used to drive reactions (cross-bridge cycling) or to regulate enzymes (phosphorylation) and heat.

  • Phosphorylation of molecules changes their shape.

  • Hydrolysis of ATP > ADP + Pi (releases heat)

Oxidation-Reduction (Redox) Reactions

• Oxidation:

  • Loss of electrons or H+

  • Gain of O-

  • Loss of energy

• Reduction:

  • Gain of electrons

  • Gain H+

  • Loss of O-

Enzymes

• Dehydrogenases: Transfer H+ and e-

• Oxidases: Transfer of oxygen

• Require help, usually vitamin B derivatives.

  • Coenzymes act as hydrogen or electron acceptors.

    • Nicotinamide adenine dinucleotide (NAD+)

    • Flavin adenine dinucleotide (FAD)

ATP Synthesis (Two Mechanisms)

• Substrate-level phosphorylation:

  • A high-energy phosphate group is transferred directly from a substrate to ADP to form ATP.

  • Occurs in the cytosol and mitochondrial matrix.

• Oxidative phosphorylation:

  • Electron transport proteins pump protons, creating a proton gradient.

  • ATP synthase uses the energy of the proton gradient to bind phosphate groups to ADP.

  • Occurs only in the mitochondrial matrix.

  • More complex, produces more ATP, but very slow

  • Chemiosmotic hypothesis

Carbohydrate Metabolism

• Oxidation of glucose:

  • C₆H₁₂O₆ + 6O₂ > 6H₂O + 6CO₂ + ATP + Heat

• Complete glucose catabolism requires three pathways:

  • Glycolysis

  • Krebs cycle

  • Electron transport chain and oxidative phosphorylation