Beyond their role as residues in proteins, amino acids participate in a number of processes such as neurotransmitter transport and biosynthesis.
In biochemistry, amino acids having both the amine and the carboxylic acid groups attached to the first (alpha-) carbon atom have particular importance.
Cysteine has its side chain in the same geometric position as the other amino acids, but the R/S terminology is reversed because of the higher atomic number of sulfur compared to the carboxyl oxygen gives the side chain a higher priority, whereas the atoms in most other side chains give them lower priority.
In some amino acids, the amine group is attached to the β or γ-carbon, and these are therefore referred to as beta or gamma amino acids.
Because all amino acids contain amine and carboxylic acid functional groups, they share amphiprotic properties.
Below p H 2.2, the predominant form will have a neutral carboxylic acid group and a positive α-ammonium ion (net charge 1), and above p H 9.4, a negative carboxylate and neutral α-amino group (net charge −1).
Many important proteinogenic and non-proteinogenic amino acids have biological functions.
amino acids; other categories relate to polarity, p H level, and side chain group type (aliphatic, acyclic, aromatic, containing hydroxyl or sulfur, etc.).
In the form of proteins, amino acid residues form the second-largest component (water is the largest) of human muscles and other tissues.
Amino acids are usually classified by the properties of their side chain into four groups.
The side chain can make an amino acid a weak acid or a weak base, and a hydrophile if the side chain is polar or a hydrophobe if it is nonpolar.