Amino Acid Metabolism Classification

Classification of Amino Acids

Classification Based on Metabolism

• Purely ketogenic amino acids enter the ketogenic pathway, e.g., Leucine
• Ketogenic and glucogenic amino acids enter both ketogenic and glucogenic pathways, e.g., Lysine, Isoleucine, Phenylalanine, Tyrosine, and Tryptophan
• Purely glucogenic amino acids enter the glucogenic pathway, e.g., all the remaining 14 amino acids

Classification Based on Nutritional Requirements

• Essential amino acids are not synthesized by the human body and need to be taken through food, e.g., Methionine, Threonine, Tryptophan, Valine, Isoleucine, Leucine, Phenylalanine, and Lysine
• Semi-essential amino acids are required in food for growing children, but not for adults, e.g., Arginine and Histidine
• Non-essential amino acids are synthesized by the human body and do not need to be taken through food, e.g., all the remaining 10 amino acids

Classification Based on Structure

• Aliphatic amino acids have an aliphatic side chain
• Aromatic amino acids have an aromatic side chain, e.g., Phenylalanine and Tyrosine
• Heterocyclic amino acids have a ring with more than one kind of atoms on the side chain, e.g., Tryptophan and Histidine
• Imino acid has a side chain attached to the amino group, e.g., Proline
• Derived amino acids are compounds derived from amino acids, e.g., Hydroxy proline and hydroxy lysine, Citrulline and Homocysteine, and Gamma Amino Butyric Acid (GABA)

Classification Based on Structure (Subclasses)

• Aliphatic amino acids can be subclassified into:
  • Mono amino mono carboxylic acids, e.g., Glycine, Alanine
  • Mono amino dicarboxylic acids, e.g., Aspartic acid, Glutamic acid
  • Di basic mono carboxylic acids, e.g., Lysine, Arginine
  • Branched chain amino acids, e.g., Valine, Leucine, Isoleucine
  • Hydroxy amino acids, e.g., Serine, Threonine
  • Sulphur containing amino acids, e.g., Cysteine, Methionine
  • Amino acids with amide group, e.g., Asparagine, Glutamine

Classification Based on Side Chain

• Amino acids with nonpolar side chains, e.g., Alanine, Valine, Leucine, Isoleucine, Methionine, Proline, Phenylalanine, and Tryptophan
• Amino acids with nonionic polar side chains, e.g., Glycine, Serine, Threonine, Cysteine, Tyrosine, Glutamine, and Asparagine