steroler

Steroler, or sterols in English, are a subgroup of steroids characterized by a hydroxyl group at position 3 of a four-ring ring system. They are essential lipids in eukaryotic cell membranes and also serve as precursors for various biologically active molecules such as steroid hormones and bile acids. Sterols are found in animals, plants, and fungi, but are not typically produced by bacteria.

The core structure of sterols consists of a tetracyclic ring system with a hydrocarbon side chain. The most well-known example is cholesterol, the primary animal sterol. In plants, major sterols include sitosterol, campesterol, and stigmasterol. Fungi synthesize ergosterol, which differs from cholesterol in ring substitutions and double-bond patterns. Desmosterol and lanosterol are notable intermediates in sterol biosynthesis.

Biological roles of sterols include regulation of membrane fluidity and permeability, contributing to membrane order and the formation of microdomains such as lipid rafts. They modulate membrane thickness and mechanical properties and are involved in signaling pathways. In many organisms, sterols are precursors to signaling molecules: cholesterol-derived steroids in animals and phytosterols influencing digestion and export of lipids in plants. Ergosterol in fungi is essential for membrane integrity and a target of several antifungal drugs.

Biosynthesis of sterols generally derives from isoprenoid precursors via the mevalonate pathway in animals and fungi, with plants utilizing related pathways to produce phytosterols. Lanosterol is a key intermediate in cholesterol synthesis, while cycloartenol is an early intermediate in plant sterol biosynthesis.

In summary, sterols are a diverse and fundamental class of steroid alcohols that shape membrane properties and provide substrates for a variety of biological processes across eukaryotes.