Glycine, ball and spoke model, c 1977.
© Science Museum / Science & Society Picture Library
Glycine (CH2NH2COOH) is the the simplest amino acid and one of the main components of proteins. When purified, it is a sweet, colourles crystalline compound. In ball and spoke molecular models of this type, each ball represents an atom of a chemical element, and can be connected to other 'atoms' by means of bonds represented by inserting the connecting spokes in holes in the balls. The number of holes in a ball represents the number of molecular bonds atoms of different elements are able to form. This is determined by an element's valency, which is dictated by the number of electrons in the outermost shell of an atom of that element. Here, the carbon atoms are represented by the green balls, Nitrogen the blue, oxygen red, and hydrogen the white.