Amino acids are the constituents of proteins. They are linked together by the ribosomes of cells to form chains called peptides. As the chain of amino acid grows, it becomes a polypeptide, and eventually a complete protein. All proteins are made up of 20 amino acids. About half of these molecules are synthesized by the body and these are known as nonessential amino acids. The amino acids that the body can’t make are obtained through the diet. These are known as essential amino acids.
All 20 amino acids have a similar structure. Each one features a carboxyl group and amino group bound to a carbon atom. Each amino acid also has a R group, which is the identifying characteristic. This list of amino acids categorizes the amino acids according to the chemistry of the R group. Amino acids with a star * are essential amino acids.
Nonpolar Aliphatic R Groups
There are seven amino acids with a nonpolar, aliphatic R group. They include glycine, alanine, proline, valine*, leucine*, isoleucine*, and methionine*.
Aromatic R Groups
There are three amino acids with aromatic R groups. They include phenylalanine*, tyrosine*, and tryptophan*.
Polar Uncharged R Groups
There are five amino acids with a polar, uncharged R group. They include serine, threonine*, cysteine, asparagine, and glutamine.
Positively Charge R Groups
There are three amino acids featuring a positively charged R group. They include lysine*, arginine, and histidine*.
Negatively Charged R Groups
The final group of amino acids contain a negatively charged R group. There are two amino acids in this group and they are aspartate and glutamate.
Reference:
Nelson, David L. Lehninger Principles of Biochemistry 4th ed. W.H. Freeman and Company. 2005