L41 BIOL 4810 Lecture Notes - Lecture 29: Beta-Sitosterol, Stigmasterol, Sterol
12 May 2020
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Document Summary
Classes of lipids: sterols: sterol, steroid nucleus: four fused rings, hydroxyl group (polar head) in the a-ring, various nonpolar side chains, the tetracycle structure of sterols is almost planar. Classes of lipids: sterol lipids cholesterol: cholesterol is the most abundant steroid in animals, major component of plasma membranes in animals, also occurs in organelle membranes, but in lesser amounts. Is a metabolic precursor of steroid hormones which regulate many physiological functions: plants contain little cholesterol and instead primarily contain stigmasterol and -sitosterol. Ergosterol- fungal cholesterol analog: drug amphotericin b has greater affinity for membrane ergosterol than cholesterol. This makes amphb specifically antifungal when dosed properly. Properties of lipids: lipids in water: hydrophilic head groups are immersed in water; hydrophobic tails extend into the air to avoid water. Bilayers: glycerophospholipids and sphingolipids have two hydrocarbon tails, due to their shape, they pack into disklike micelles, glycerophospholipids are abundant in membranes, likely promoting their formation of the bilayer.
