15.1 - Lipids

• Lipids are not water-soluble biomolecules

• Lipid categories include waxes, glycerol triglycerides, glycerophospholipids, sphingolipids, and steroids.

15.2 - Fatty Acids

• Unbranched carboxylic acids are fatty acids that typically contain an equal quantity of carbon atoms (12 to 20).

  • Saturated, monounsaturated, or polyunsaturated with two or double bonds may be fatty acids.

• Almost always the double connection is cis in unsaturated fatty acids.

15.3 - Waxes and Triacylglycerols

• Wax is an ester of a fatty acid with a long chain of alcohol.

  • Triacylglycerols are three long-chain fatty acid esters of glycerol.

• Fats have higher melting points than most vegetable oils, which contain more saturated fatty acids.

15.4 - Chemical Properties of Triacylglycerols

• Triacylglycerol hydrogenation transforms double bonding into single bonding.

  • Glycerol and fatty acids are produced when the ester bonds are hydrolyzed in triacylglycerols when strong acids are present.

• In saponification, glycerol and fatty acid salts are generated by triacylglycerol heated on a strong basis.

15.5 - Phospholipids

• Glycerophospholipids are glycerol esters with two fatty acids and an amino alcohol phosphate.

• Sphingomyelin forms an amide bond to fatty acid in amino alcohol sphingosine and a phosphodiester bonds to phosphate and amino alcohol.

15.6 - Steroids: Cholesterol, Bile Salts, and Steroid Hormones

• Steroids are lipids that contain the four-ring fused structure of the steroid nucleus.

  • Cholesterol, bile salts, and steroid hormones are part of the steroids.

• Synthesized with cholesterol, bile salts mix and break them apart with water-insoluble fats during digestion.

• The triacylglycerides are transported from the intestines and liver, such as chylomicrons and LDL, to fat cells and muscles for storage and energy.

• HDL carries cholesterol from tissue to the liver for removal

• Steroid hormones are structurally closely associated with cholesterol and their synthesis depends upon cholesterol.

  • For sexual properties and reproductive properties, sex hormones such as estrogens and testosterone are responsible.

• Adrenal corticosteroids, such as aldosterone and cortisone, regulate the cellular water balance and blood glucose.

15.7 - Cell Membranes

• The semi-permeable membrane which separates the cellular content from the external fluids is surrounded by all animal cells.

• The membrane consists of a lipid bilayer with two rows of phospholipids.

• The lipid bilayer contains proteins and cholesterol and the surface is attached to the carbohydrates.

• Nutrients and waste products are moved via passive transport (diffusion), easier transport, or active transport through the cell membrane.