MDCAT Amino Acids & Proteins 2026

Amino Acid Properties

• 20 standard amino acids; 9 essential (humans cannot synthesise)
• Zwitterion form at physiological pH (NH₃⁺/COO⁻)
• Isoelectric point (pI): pH at which net charge = 0

Protein Structure

• Primary — amino acid sequence (peptide bonds)
• Secondary — α-helix, β-sheet (H-bonds)
• Tertiary — 3D folding (R-group interactions)
• Quaternary — multiple subunits (haemoglobin)