User:Nysin/Amino

Structures and symbols of the 20 amino acids which are directly encoded for protein synthesis by the standard genetic code

• 
  L-Alanine
  (Ala / A)
• 
  L-Arginine
  (Arg / R)
• 
  L-Asparagine
  (Asn / N)
• 
  L-Aspartic acid
  (Asp / D)
• 
  L-Cysteine
  (Cys / C)
• 
  L-Glutamic acid
  (Glu / E)
• 
  L-Glutamine
  (Gln / Q)
• 
  Glycine
  (Gly / G)
• 
  L-Histidine
  (His / H)
• 
  L-Isoleucine
  (Ile / I)
• 
  L-Leucine
  (Leu / L)
• 
  L-Lysine
  (Lys / K)
• 
  L-Methionine
  (Met / M)
• 
  L-Phenylalanine
  (Phe / F)
• 
  L-Proline
  (Pro / P)
• 
  L-Serine
  (Ser / S)
• 
  L-Threonine
  (Thr / T)
• 
  L-Tryptophan
  (Trp / W)
• 
  L-Tyrosine
  (Tyr / Y)
• 
  L-Valine
  (Val / V)

IUPAC/IUBMB now also recommends standard abbreviations for the following two amino acids:

• 
  L-Selenocysteine
  (Sec / U)
• 
  L-Pyrrolysine
  (Pyl / O)

Sometimes the specific identity of an amino acid cannot be determined unambiguously. Certain protein sequencing techniques do not distinguish among certain pairs. Thus, the following codes are used:

• Asx (B) is "asparagine or aspartic acid"
• Glx (Z) is "glutamic acid or glutamine"
• Xle (J) is "leucine or isoleucine"

In addition, the symbol X is used to indicate an amino acid that is completely unidentified.

Following is a table listing the one-letter symbols, the three-letter symbols, and the chemical properties of the side chains of the standard amino acids. The masses listed are based on weighted averages of the elemental isotopes at their natural abundances. Note that forming a peptide bond results in elimination of a molecule of water, so the mass of an amino acid unit within a protein chain is reduced by 18.01524 Da.

Side chain properties

Note: The pKa values of amino acids are typically slightly different when the amino acid is inside a protein. Protein pKa calculations are sometimes used to calculate the change in the pKa value of an amino acid in this situation.

Gene expression and biochemistry

UAG is normally the amber stop codon, but encodes pyrrolysine if a PYLIS element is present.
UGA is normally the opal (or umber) stop codon, but encodes selenocysteine if a SECIS element is present.
The stop codon is not an amino acid, but is included for completeness.
An essential amino acid cannot be synthesized in humans and must, therefore, be supplied in the diet. Conditionally essential amino acids are not normally required in the diet, but must be supplied exogenously to specific populations that do not synthesize it in adequate amounts.

Remarks