The purpose of this module is to expand upon the introduction to proteins given in BIOL111. Our approach is to use specific examples to demonstrate different aspects of protein structure, and to illustrate the way that the different properties of individual amino acids contribute to the function of the proteins they make up. The course is split into two linked themes. Firstly, an introduction to the major structural features of proteins is given, with an emphasis on how protein structure relates to function. Secondly, an introduction to enzyme biochemistry is presented. We consider how enzymes catalyse biochemical reactions, how their activities can be described quantitatively, and how enzymes are regulated within the cell.