ABSTRACT
This chapter discusses structure and to introduce the subject will borrow some ideas from biochemists and molecular biologists. In describing protein structure it is usual to consider four levels of organization, termed primary, secondary, tertiary and quaternary structure. Primary structure refers to the sequence of amino acids that makes up the polymer chain of a particular protein. Secondary structure is the ordered conformation that the chains can twist itself into. The two most common are the a-helix and the ß-sheet; the former looks like a coiled spring, while the latter looks like an extended zig-zag. Tertiary structure refers to how a single chain can be folded in on itself. Finally, quaternary structure refers to how different molecules can pack to form an organized unit. The interaction energy between molecules or segments can be considered to consist of two components, arising from repulsive and attractive intermolecular forces, respectively.
