2.1.2 Metabolism

• Metabolism is a catch-all term used to describe all the chemical reactions that take place within cells and organisms
• Metabolism can be thought of as the chemical reactions of life
  • The molecules involved are metabolites

• Many reactions of metabolism take place in multiple stages
  • Each stage is catalysed by a separate enzyme

• A series of interlinked metabolic reactions is called a metabolic pathway
• Metabolic reactions can be classified broadly as anabolic or catabolic

• Anabolic reactions are involved with the building of large molecules from smaller ones
• Examples include;
  • Photosynthesis, where CO₂ and water are built up into complex sugars
  • Protein synthesis, where amino acids are joined together in sequence
  • The buildup of fat stores ahead of animal hibernation

• Anabolic reactions often include condensation reactions
• Anabolic reactions are endergonic (they require an input of energy to take place)
  • Energy-storing products are the end result

• Catabolic reactions are involved with breaking down large molecules into smaller ones
• These reactions are often carried out to release energy for cellular processes and for the excretion of waste
• Examples include:
  • Respiration, where CO₂ and water are produced from the breakdown of sugars
  • Deamination of proteins to release urea
  • The depletion of fat stores during animal hibernation

• Catabolic reactions often include hydrolysis reactions
• Catabolic reactions are exergonic (free energy is released for cellular processes or as excess heat)

Comparison of Anabolism and Catabolism Table