Steroids
Structure: Four fused rings (three six-membered, one five-membered).
Functions:
Membrane Structure: Cholesterol regulates membrane fluidity and permeability.
Hormonal Roles: Includes sex hormones and corticosteroids, essential for metabolism, immunity, and reproduction.
Cardiac Glycosides
Structure: Steroid core linked to sugar units via glycosidic bonds.
Physiological Effects:
Enhance heart contractions by inhibiting the Na⁺/K⁺-ATPase pump, increasing calcium levels.
Used to treat heart failure and arrhythmias with precise dosing due to a narrow therapeutic index.
Triterpenoids
Structure: Built from six isoprene units (30 carbons), forming complex cyclic or acyclic structures.
Roles in Plants: Defense against pests, precursors to steroids.
Pharmacological Effects: Anti-inflammatory, anticancer, and antiviral properties, widely used in drug development.