Medical Biochemistry Lecture 1: Amino Acids

Amino Acids and Peptides

• Proteins, which are polymers of amino acids, carry out all major structural and functional aspects of the body.
• There are 20 L-α-amino acids present in the human body, determined by three-letter genetic codes.

Structure of Amino Acids

• Amino acids, except proline, are alpha amino acids, with the amino group attached to the same carbon atom as the carboxyl group.

Classification of Amino Acids

• There are five ways to classify amino acids: by chemical nature, structure of the side chain, nutritional requirement, metabolic product, or nature/polarity of the side chain.

Classification Based on Chemical Structure of Side Chain

• Not specified in the provided text.

Classification of Amino Acid Based on Metabolism

• Ketogenic amino acids: yield acetoacetate or its precursors upon catabolism (e.g., Leucine and Lysine).
• Ketogenic and glucogenic amino acids: partially yield acetoacetate and pyruvate or citric acid cycle intermediates.
• Glucogenic amino acids: yield pyruvate or citric acid cycle intermediates, used for gluconeogenesis and glucose synthesis.

Classification Based on Nutritional Requirements

• Essential amino acids: Isoleucine, Leucine, Threonine, Lysine, Methionine, Valine, Phenylalanine, and Tryptophan, which cannot be synthesized by humans and must be obtained through diet.
• Partially essential (semi-essential) amino acids: Histidine and Arginine, required for growing children but not adults.
• Non-essential amino acids: Alanine, Asparagine, Aspartic acid, Cysteine, Glutamine, Glutamic Acid, Glycine, Proline, Serine, and Tyrosine, which can be synthesized by the body.

Classification Based on Nature or Polarity of Side Chain

• Hydrophilic (polar) amino acids
• Hydrophobic (nonpolar) amino acids

Optical Activity

• Amino acids with an asymmetric carbon atom have different groups attached to the same carbon atom.