Arginine molecule. Computer model of a molecule of the amino acid arginine. Atoms are represented as spheres and are colour-coded: carbon (green), hydrogen (white), oxygen (red) and nitrogen (blue). Amino acids are the building blocks of proteins. Arginine is a semi-essential amino acid. It can be synthesised by the body and so does not need to come from the diet. However, infants and children are unable to synthesis sufficient quantities for normal growth and so must obtain some from animal or plant proteins. Arginine plays an important role in the production of urea, the principal form in which mammals excrete nitrogenous compounds from the body. It also plays a role in wound healing and cell division.