Overview of Biochemical Reactions in Metabolism

Key Types of Metabolic Reactions

• Anabolic Reactions (Synthesis Reactions)
  • Build larger molecules from smaller ones (monomers).
  • Input energy to form chemical bonds.
• Catabolic Reactions (Decomposition Reactions)
  • Break down chemical bonds using water (hydrolysis).
  • Release stored energy from chemical bonds.

Cellular Respiration

• Breakdown of food material to capture energy as ATP.
• Oxygen is used to repurpose energy.
• Metabolic processes repurpose energy from nutrients to ATP.

ATP (Adenosine Triphosphate)

• Energy currency of the cell.
• Energy stored in high-energy phosphate bonds.
• Enzymes facilitate ATP synthesis.
• ATP is used for cellular work by transferring energy to new molecules.

Stages of Metabolism

1. Ingestion and Digestion
   • Catabolic breakdown of carbohydrates, proteins, lipids.
   • Absorption and transportation to tissues.
2. Cellular Processing
   • Synthesis of lipids, proteins, glycogen.
   • Manufacturing of ATP.

Methods of ATP Generation

• Substrate-Level Phosphorylation
  • Direct transfer of a phosphate group to ADP.
  • Involves an enzyme and is inefficient.
• Oxidative Phosphorylation
  • Energy from chemical bonds adds phosphate to ADP.
  • Very efficient, uses intermediates from glucose breakdown.

Energy and Electrons

• Electrons have energy, can be potential or kinetic.
• Chemical bonds represent potential energy.
• Energy from bonds is used for chemical, transport, and mechanical work.

Energy Efficiency

• 60% of energy is lost as heat during ATP breakdown.
• ATP is efficient due to high-energy phosphate bonds.

First Law of Thermodynamics

• Energy is not created or destroyed, only repurposed.
• Energy conversion examples: photosynthesis, ATP synthesis.

Chemical Reactions

• Exergonic Reactions: Release energy.
• Endergonic Reactions: Require energy input.
• Activation energy is needed to initiate reactions.
• Enzymes lower activation energy, increasing reaction likelihood.

Coupling Reactions

• Favorable exergonic reactions are coupled with unfavorable endergonic reactions.
• Example: ATP breakdown (exergonic) with peptide bond formation (endergonic).