1.1 Objective:
To describe the general structure of steroid hormones and the impact of three-dimensional shape on steroid-protein interactions.

Structurally, steroids are derivatives of a reduced 3-ring phenanthrene molecule with a fourth (”D”) ring added. The carbons of the A, B, C, and D rings are conventionally numbered 1 through 17.

Steroid hormones interact with cellular receptors. Steroid hormones and their intermediates interact with intracellular enzymes which catalyze conversions to more or less active molecules. The specificity of a compound for its cognate receptor or an enzyme is based on its three dimensional structure.

Three-dimensional shape is determined by the orientation of the substituents, which can be in either the a or b orientation relative to the rings. For example, if a functional group on position 5 is in the a orientation and a substituent on position 10 is in the b orientation, then the A and B rings will assume a trans configuration. Conversely, if both substituents are in the b orientation, then the A and B rings will assume the cis configuration, which differs significantly from the trans configuration in three dimensional shape.