Sterols

Sterols

Sterols, also known as steroid alcohols, are a subgroup of steroids and an important class of organic molecules. They occur naturally in plants, animals, and fungi, with the most familiar type of animal sterol being cholesterol. Sterols are a crucial component of cell membranes, where they modulate fluidity and permeability.

Structure

Sterols are characterized by their structure, which consists of a hydroxyl group at the 3-position of the A-ring, and a hydrocarbon side chain at the 17-position. The core structure of sterols is a four-ring system known as the cyclopentanoperhydrophenanthrene ring system. This structure is shared with other steroids, but sterols are distinguished by the presence of the hydroxyl group.

Types of Sterols

Animal Sterols

• Cholesterol: The most well-known sterol, cholesterol is essential for the formation of cell membranes, synthesis of vitamin D, and production of steroid hormones. It is found in all animal cells and is a precursor for bile acids.

Plant Sterols

• Phytosterols: These are plant-derived sterols that are structurally similar to cholesterol. Common phytosterols include beta-sitosterol, campesterol, and stigmasterol. They are known to reduce cholesterol levels in humans by competing with cholesterol for absorption in the digestive system.

Fungal Sterols

• Ergosterol: Found in fungi, ergosterol is a precursor to vitamin D2. It is an important component of fungal cell membranes, similar to the role of cholesterol in animal cells.

Biological Functions

Sterols play several critical roles in biological systems:

• Membrane Structure: Sterols are integral components of cell membranes, where they help maintain membrane fluidity and integrity.
• Precursor Molecules: Many sterols serve as precursors to biologically important molecules, such as steroid hormones, bile acids, and vitamins.
• Signal Transduction: Sterols are involved in cell signaling pathways, influencing processes such as cell growth and differentiation.

Health Implications

The balance of sterols in the body is crucial for health. Elevated levels of cholesterol, particularly low-density lipoprotein (LDL) cholesterol, are associated with an increased risk of cardiovascular diseases. Conversely, plant sterols have been shown to lower LDL cholesterol levels and are often included in functional foods and dietary supplements.

Also see

• Cholesterol
• Phytosterols
• Ergosterol
• Steroid
• Lipid