A steroid is a member of a structural family based on a characteristic fused-ring carbon framework, usually three six-membered rings and one five-membered ring. Cholesterol, bile-derived compounds and many signalling molecules share variations of this skeleton.
Substituents, oxidation states and especially ring-junction stereochemistry change molecular shape and function. Thus “steroid” is a structural classification, not a synonym for one hormone or one biological effect. Removing or modifying a side chain can preserve the underlying steroid framework while changing biochemical behaviour substantially.
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