Question

Describe the structure of a steroid. Be detailed.

Answer 1

The steroid core structure is composed of seventeen carbon atoms, bonded in four "fused" rings: three six-member cyclohexane rings (rings A, B and C in the first illustration) and one five-member cyclopentane ring (the D ring). Steroids vary by the functional groups attached to this four-ring core and by the oxidation state of the rings. The fused six-membered cyclohexane rings each have the chair conformation. Each member of the steroid family has a structure that differs from this basic skeleton in the degrees of unsaturation within the ring system and the identities of the hydrocarbon side chain substituents attached to the rings. These substituents are in most cases oxidized to alcohol, aldehyde , ketone , or carboxylic acid functional groups.

Steroids are lipids because they are hydrophobic and insoluble in water, but they do not resemble lipids since they have a structure composed of four fused rings.

Cholesterol is the most common steroid and is the precursor to vitamin D, testosterone, estrogen, progesterone, aldosterone, cortisol, and bile salts