Polarised light micrograph of crystals of the amino acid arginine (ARG). There are twenty standard amino acids, which form the basic building blocks of all living matter. Amino acids combine to form proteins. The linkage between two amino acids is called a peptide bond & the amino acids so joined are referred to as peptides. A protein molecule consists of anywhere from a hundred to several thousand amino acids, linked together to form polypeptide chains. Magnification: X100 at 5x4 inch, X28 at 35mm size.