A Steroid is an organic compound with four rings arranged in a specific configuration . Examples include the dietary lipid cholesterol. The sex hormones estradiol and testosterone and the anti-inflammatory drugdexamethasone . Steroids have two principal biological functions: certain Steroids such as cholesterol are important components of cell membranes which after membrane fluidity and many steroids are signaling molecules which activate steroid hormones receptors. The steroid core structure is composed of seventeen carbon atoms , bonded in four fused rings. Three six member cyclohexane ring ( ring A, B and C in the first illustration ) and one five member cyclopentane rind(the D ring). Steroids vary by the functional group attached to this four ring core and by the oxidation state of the rings. Sterols are forms of steroids with a hydroxyl group at position three and skeleton derived from cholestane. They can also vary more ...
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