Lipids: class of naturally occurring compounds that are insoluble in water but soluble in nonpolar solvents.

17.1  Waxes

Waxes: esters of long-chain fatty acids and long-chain alcohols.  Low melting semi-solids.

17.2  Triglycerides

Triglycerides: triesters of long-chain fatty acids and glycerol.

        Simple triglycerides: made from glycerol and three molecules of one kind of fatty acid

.        Mixed triglycerides: triesters of glycerol with different fatty acid components.        

        Fats: triglycerides that are solid at room temp. Have saturated acids.        

        Oils: triglycerides that are liquid at room temp.  Unsaturated chains.

Hydrogenation is the reaction that converts oils to fats.  Uses powdered nickel catalyst.

Rancidityof triglycerides is caused by oxidation of the double bonds.  Produces epoxides, aldehydes and acids with nasty odors.  Antioxidants help to keep this reaction from occurring.

Saponification: Hydrolysis of oils or fats by boiling them with strong base (like NaOH).  Makes soaps.  Glycerol is a by-product of this reaction.

17.3  Lipid Compostion of Cell Membranes

Cell membranes act as selective barriers due to the composition of lipids and proteins.  Most lipids in cell membrane are complex lipids.

        2 types of complex lipids = phospholipids (phosphoglycerides and sphingomyelins) and         glycolipids.

Phosphoglyceride: a triglyceride in which one of the ester linkages is with phosphoric acid or a substituted phosphoric acid.

Phosphotidyl choline: consists of choline attached to phosphoric acid (+glycerol +fatty acid).  The choline end of this molecule is hydrophilic, by the other end is hydrophobic.  Phosphotidyl choline readily forms liposome structures.

17.4  Structure of Liposomes and Cell Membranes

In water the phospholipid molecules form spheres called liposomes.  Liposomes are packages of water surrounded by a lipid bilayer.  The nonpolar tails of the molecules are toward the center of the bilayer, and the polar heads make up the two surfaces.  Cell membranes consist of these lipid bilayers.  When these bilayers have high proportions of saturated fatty acids they are more rigid.  High proportions of unsaturated fatty acids make it more flexible.

17.5  Steroids

Steroids: family of lipids found in plants and animals.  Have structure based on four fused rings (three 6 sided rings and one sided ring).  Cholesterol is a steroid, specifically a sterol because it contains a hydroxyl group and no carboxyl or aldehyde group.

17.6 Steroid Hormones

Steroid Hormones are secreted by adrenal glands and testes.  Corticoids, glucocorticoids and mineralcorticoids are secreted by the adrenal glands in different zones.

17.7  Male Sex Hormones

Testosterone is the principal male sex hormone, produced in testes.  Anabolic steroids: synthetic, structurally similar to testosterone.

17.8

 The estrogens and progesterone are primary female sex hormones, produced by ovaries.