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BIO 181 (27)

Lecture on Lipids and Membranes

5 Pages

Course Code
BIO 181
Kenneth Mossman

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Lipids and Membranes  What is a lipid?  A carbon-containing biological molecule that is largely nonpolar and hydrophobic o Most are hydrocarbons that contain only hydrogen and carbon atoms Composed of building blocks called fatty acids A fatty acid is a hydrocarbon chain bonded to a carboxyl (COOH) functional group Most fatty acids have an even number of carbon atoms They’re synthesized by joining two-carbon acetyl groups  Fatty acid saturation  Saturation refers to the degree to which the carbon atoms in a fatty acid are linked to hydrogen atoms  Unsaturated fatty acids possess one or more double covalent bonds between 2 or more carbon atoms o The double bonds produce kinks that prevent rotation and thus limit the flexibility of the hydrocarbon chain  Types of lipids: Steroids  Unique family of lipids distinguished by a four-ring structure o They’re synthesized by cycling a special triterpenoid hydrocarbon known as squalene o Steroid hormones are important signaling molecules, and sterols like cholesterol are integral components of mammalian cell membranes  Types of lipids: Fats  Composed of 3 fatty acid monomers linked together via a glycerol molecule o Triglycerides Synthesized through series of dehydration (condensation) reactions that join the carboxylic acid groups of fatty acids to the hydroxyl groups of glycerol These covalent bonds are ester linkages  Types of lipids: Phospholipids  Consist of glycerol linked to a phosphate group (PO 43) and either two chains of isoprene or 2 fatty acids o Synthesized like fats o Amphipathic  They contain both hydrophilic and hydrophobic regions  Head contains polar covalent bonds and atoms that carry charges  Tail contains nonpolar hydrocarbon chains of fatty acids  Lipid Membranes and Bilayers  Simplest membrane structure, a micelle, consist of a single layer of amphipathic lipids that enclose a hydrophobic core  Lipid bilayers form when two sheets of phospholipid molecules arrange themselves such that the head groups in each layer face outwards t
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