Medical Definition of Amino acid symbols

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Amino acid symbols: Symbols that stand for the amino acids, the building blocks of protein. Each amino acid has both a three-letter symbol and a single-letter symbol. For example, the three-letter and single-letter symbols for alanine are Ala and A. The three-letter symbols (such as Ala) are much more widely used than the single letter ones (such as A).

Therefore, the following list is limited to the three-letter symbols and is further limited to those 20 alpha-amino acids specified by the genetic code:

  • Alanine: Ala
  • Arginine: Arg
  • Asparagine: Asn
  • Aspartic acid: Asp
  • Cysteine: Cys
  • Glutamic acid: Glu
  • Glutamine: Gln
  • Glycine: Gly
  • Histidine: His
  • Isoleucine: Ile
  • Leucine: Leu
  • Lysine: Lys
  • Methionine: Met
  • Phenylalanine: Phe
  • Proline: Pro
  • Serine: Ser
  • Threonine: Thr
  • Tryptophan: Trp
  • Tyrosine: Tyr
  • Valine: Val

These three-letter symbols for amino acids are used not only to refer to an individual amino acid but also to present the amino acid sequence of a polypeptide or a protein. For example, part of the sequence of insulin reads: Gly-Ile-Val-Glu-Gln-Cys-Cys-Ala-Ser-Val. The N-terminal residue of the polypeptide or protein is by convention always on the left and the sequence reads from left-to-right toward the C-terminal residue of the polypeptide or protein.

Reviewed on 12/11/2018

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