Medical Definition of Amino acid symbols

Reviewed on 3/29/2021

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.



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