LEHNINGER PRINCIPLES OF BIOCHEMISTRY David L. Nelson and Michael M. Cox LEHNINGER PRINCIPLES OF BIOCHEMISTRY Sixth Edition CHAPTER 10 Lipids © 2013 W. H. Freeman and Company

Lipids Lipids are a family of compounds that are relatively insoluble in water. Lipids play major roles in: energy storage membrane structure Other roles of lipids: enzyme cofactors light-absorbing pigments hormones signal transduction molecules

Lipids often contain fatty acids molecules. Fatty acids are carboxylic acids with hydrocarbon chains from 4 to 36 carbons long. The most common biological fatty acids have an even number of carbons between 12 and 24 carbons. Fatty acids can be saturated (no double bonds) or unsaturated (containing double bonds) double bonds are in the cis configuration. Nomenclature: 16:0 is a 16 carbon fatty acid with no double bonds 20:2 (D9,12) is a 20 carbon fatty acid with double bonds after C-9 and C-12 (C-1 is COOH)

Packing of fatty acids into stable aggregates

Triacylglycerols contain three fatty acids esterified to a glycerol backbone

Triacylglycerols are stored energy in fat cells and plant seeds

The greater the percentage of saturated fatty acids in food fats the higher the melting temperature

Waxes are esters of long chain fatty acids

Common types of storage and membrane lipids

Glycerophospholipids, the main lipid component of biological membranes, contain two fatty acids esterified to a glycerol phosphate backbone

Structure of phosphatidylcholine

Glycerophospholipids with ether-linked fatty acids Abundant in the heart Important in inflammatory response

Archaea contain unique membrane lipids

Sphingomyelin is similar in structure to phosphatidylcholine

Glycosphingolipids as determinants of blood groups Glycosphingolipids contain the blood group antigens present on the surface of red blood cells

Blood Groups The carbohydrates on certain sphingolipids determine your blood group, affecting the blood type you can receive in a transfusion. These sphingolipids are on the surface of erythrocytes. Type A individual has A antigens and anti-B antibodies Type B individual has B antigens and anti-A antibodies Type AB individual has A and B antigens and neither anti-A nor anti-B antibodies Type O individual has O antigen and both anti-A and anti-B antibodies Example: Type A individual cannot receive Type B blood. Antigen-antibody interaction causes agglutination

The specificities of phospholipases, enzymes that cleave glycerophospholipids

Sterols have four fused carbon rings Cholesterol is the main sterol in animal tissues

Bile acids are synthesized from cholesterol Bile acids aid in emulsification of dietary fat in the intestine

Arachidonate is the precursor for eicosanoid hormones Eicosanoids are involved in pain, fever, inflammation

Other sterols are synthesized from cholesterol

Vitamin D is produced in the skin by UV irradiation of 7-dehydrocholestreol

Vitamin A is a lipid belonging to the isoprenoid family

Some biologically important isoprenoids