Introduction: Protein structure
Proteins seen in nature have evolved to perform specific functions. Functional properties are dependent on their three-dimensional structures which arise because particular sequences of amino acids in linear polypeptide chains (primary structure) fold to generate small elements of secondary structure (β-sheets, α-helices and loops). These combine to form compact domains with specific three-dimensional structure (tertiary structure) which can in turn join with other polypeptide chains to create large multimers (quaternary structure). The three-dimensional structure brings together the various amino acids that form the functional region or active site.
You can get more detail on protein structure at: http://en.wikipedia.org/wiki/Protein_structure
In this tutorial, you will work with Bovine Ribonuclease A.
Section 1: Viewing a 3D structure
Section 2: Simplifying the view
Section 3: Selecting parts of the structure
Section 4: Showing useful information