Lysine is an α-amino acid that is used in the biosynthesis of proteins. Lysine is a building block for protein. It contains an α-amino group, an α-carboxylic acid group, and a side chain lysyl, classifying it as a basic, charged, aliphatic amino acid. It’s an essential amino acid because your body cannot make it, so you need to obtain it from food. It’s important for normal growth and muscle turnover and used to form carnitine, a substance found in most cells of your body. It helps transport fats across your cells to be burned for energy (see: Wikipedia).