Overview of Metabolism

• Metabolism involves biochemical reactions that are vital for cellular functions.
• Focus on two categories: catabolism and anabolism.

Redox Reactions

• Redox reactions involve oxidation and reduction processes where electrons are transferred between molecules.
• Two important terms:
  • Oxidation: Loss of electrons
  • Reduction: Gain of electrons
• Example:
  • In catabolism, glucose and fats are oxidized incrementally, releasing energy slowly instead of in a single burst.
  • This energy is sometimes released as heat, with other portions captured for ATP synthesis.

Importance of Electron Carriers

• Key carriers include NAD (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide).
  • Oxidized forms: NAD⁺ and FAD
  • Reduced forms: NADH and FADH₂
• NAD and FAD serve as electron transporters, transferring electrons during catabolic processes to drive ATP synthesis through oxidative phosphorylation.

Proton Motive Force and ATP Synthase

• The proton motive force is crucial for ATP synthesis during oxidative phosphorylation.
• Energy derived from the flow of protons through ATP synthase is used to convert ADP to ATP.
• ATP synthesis: Ends with a net input of energy (endergonic process).

Catabolism vs. Anabolism

• Catabolism: Generally oxidative, involving the breakdown of substrates and energy release.
• Anabolism: Generally reductive, involving the building of complex molecules, where substrates become more reduced.

Dehydrogenases and Their Role

• Dehydrogenases: Enzymes that catalyze redox reactions by transferring electrons (often to NAD⁺ or FAD).
• Example: Lactate dehydrogenase reduces pyruvate to lactate and oxidizes NADH to NAD⁺.

Types of Biochemical Reactions

• Cleavage Reactions: Involve breaking of chemical bonds (homolytic vs. heterolytic).
• Isomerization Reactions: Rearrangement of molecular structure without changing the formula
  • Example: Glucose-6-phosphate to Fructose-6-phosphate
• Elimination Reactions: Removing small molecules (e.g., water) to form double bonds.

Phosphoryl Group Transfer and ATP

• ATP: The primary energy currency of the cell, effectively used through two mechanisms:
  1. Simple Hydrolysis: Releases energy without formation of a phospho-substrate intermediate.
  2. Phosphorylated Intermediate Formation: ATP is hydrolyzed, transferring phosphate to form intermediates that drive energetically unfavorable reactions.
• High Energy Intermediates: Molecules like phosphoenolpyruvate (PEP) and 1,3-bisphosphoglycerate (1,3-BPG) that readily transfer phosphate to ADP to generate ATP via substrate-level phosphorylation.

Standard Free Energy Changes

• Standard Free Energy Change: Enthalpy changes during reactions which do not always reflect the actual energy change in living cells (delta G° vs. delta G).
• Example: Standard delta G for ATP hydrolysis is −30.5 kJ/mol, but actual values may vary depending on intracellular concentrations.

Acetyl CoA

• Acetyl CoA: A crucial metabolic intermediate in the conversion of carbohydrates, fats, and proteins into energy via the TCA cycle.
• Contains a thioester bond which releases energy upon hydrolysis.

Conclusion and Future Topics

• The importance of ATP and acetyl CoA in metabolism is paramount for energy generation.
• Next, focus on glycogen metabolism and the subsequent steps of cellular respiration (glycolysis, TCA cycle, and oxidative phosphorylation).