Steroid
Organic compounds with four fused rings, vital for membranes and signaling.
A steroid is an organic compound with four fused rings (designated A, B, C, and D) arranged in a specific molecular configuration. Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and as signaling molecules. Examples include the lipid cholesterol, sex hormones estradiol and testosterone, anabolic steroids, and the anti-inflammatory corticosteroid drug dexamethasone.
- core_structure
- Gonane (cyclopentanoperhydrophenanthrene), composed of seventeen carbon atoms in four fused rings
- biological_functions
- Cell membrane components and signaling molecules
- key_examples
- Cholesterol, estradiol, testosterone, anabolic steroids, dexamethasone
- sources
- Manufactured in cells from sterol precursors: cholesterol and lanosterol (in opisthokonts) or cycloartenol (in plants), all derived from squalene
- naming_basis
- Named after sterol cholesterol, from Greek chole- 'bile' and stereos 'solid'
Lore & Background
The steroid nucleus, called gonane or cyclopentanoperhydrophenanthrene, is composed of seventeen carbon atoms bonded in four fused rings: three six-member cyclohexane rings (A, B, and C) and one five-member cyclopentane ring (D). Steroids vary by functional groups attached to this core and by the oxidation state of the rings. Sterols are forms of steroids with a hydroxy group at position three and a skeleton derived from cholestane. Modifications can include cutting one of the rings, as in secosteroids such as vitamin D3.
Reader's Guide
Steroids are fundamental to biology, serving as both structural components of cell membranes and as signaling molecules that regulate numerous physiological processes. Their core structure, gonane, allows for immense diversity through variations in functional groups, ring modifications, and stereochemistry. The naming convention for steroids is based on the parent hydrocarbon skeleton (e.g., pregnane, androstane) with suffixes and prefixes indicating functional groups and their positions. The α and β notation denotes stereochemistry relative to the ring plane, distinct from the R/S convention. This systematic nomenclature enables precise identification of thousands of naturally occurring and synthetic steroids, which are found in fungi, plants, and animals. Their significance spans from essential roles in membrane fluidity to medical applications as hormones and anti-inflammatory drugs.
Did You Know?
- All steroids are manufactured in cells from sterol precursors: cholesterol and lanosterol (in opisthokonts) or cycloartenol (in plants), all produced via cyclization of the triterpene squalene.
- The steroid nucleus gonane is composed of seventeen carbon atoms in four fused rings: three six-member cyclohexane rings and one five-member cyclopentane ring.
- Cutting Ring B of a steroid produces secosteroids, one of which is vitamin D3.
- The letters α and β denote absolute stereochemistry at chiral centers in steroids, with α-bonds depicted as dashed wedges and β-bonds as solid wedges.
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