21. Classification of lipids. Non-hydrolyzable lipids. Terpenes and steroids. Examples of biologically significancant compounds: β -carotene, retinol (vitamin A). Retinal – visual perception in humans. Cholesterol and D group vitamins. Sex hormones. Bile acids.

Isoprene and isoprenoid lipids.

• Formula: C5H8
• Structure: CH2=C(CH3)CH=CH2 (two double bonds, methyl group on second carbon)
• Classification:
• Five-carbon diene (five carbons, eight hydrogens)
• 2-methyl-1,3-butadiene (specific type of butadiene with methyl group placement)
• Isoprene is a colorless, volatile liquid hydrocarbon.
• It's a building block for many naturally occurring compounds called isoprenoids (e.g., natural rubber).
• It's produced by plants and animals (including humans).

Isoprenoids

• Group of lipids synthesized from five-carbon isoprene unit.
• Subgroups of Isoprenoids:
• 1. Terpenes (Terpenoids)
• Largest and most diverse group.
• Found in essential oils.
• Roles in plant defense, pigmentation, and signaling.
• Widely used in perfumery, pharmaceuticals, and food additives.
• 2. Fat-Soluble Vitamins
• Derived from isoprenoid compounds.
• Examples: Vitamin A (retinol), Vitamin E (tocopherol), Vitamin K.
• Essential for vision, antioxidant defense, and blood clotting.
• 3. Steroids
• Characteristic structure with four fused rings.
• Examples: Cholesterol, testosterone, estrogen, cortisol, bile acids.
• Roles in cell membrane structure, hormone regulation, and metabolism.
• Isoprenoids play crucial roles in various biological processes and are important targets in drug development and research.