Biochemistry

1. Biochemistry Lipids

2. Lipids Lipids are biochemicals which are not water soluble since they more closely resemble hydrocarbons. Included in this class are fats, oils, some vitamins and hormones, and an important part of cell membranes and nerve linings. They serve as energy storage, structural molecules, and starter materials for other important biochemicals

3. Lipids Classification: Saponifiable�can be hydrolyzed by NaOH to make soap Non-saponifiable�cannot be hydrolyzed, includes sterols such as cholesterol Saponifiable lipids are further subdivided: Simple- made of fatty acids plus alcohol Compound- either phospho- or glyco- lipids, which contain phosphate or sugar groups as well as fatty acids

4. Fats & Oils Simplest lipids, called triacylglycerols or simply triglycerides. Main form of fat storage in plants, animals, and man. Males store 21% fat on average, females 26%.

5. Simple Lipids�Fatty Acids Simple triglycerides contain the same fatty acid in all three positions; mixed triglycerides contain two or three different fatty acids Fatty acids are carboxylic acids with from 4 to 20 carbons in the chain. The chain can be saturated (only single bonds) or unsaturated (one or more double bonds in the chain), Saturated are usually solid at room temperature, unsaturated are usually liquid

6. Fatty Acids The difference between fats and oils has to do with the number of unsaturated fatty acids present. Butter, lard, and �Crisco� have mostly saturated fats. Vegetable oils have a much higher concentration of unsaturated fats.

7. Essential Fatty Acids Fatty acids which cannot be made by the body, but are important for health and growth are called essential. Linolenic acid, found mostly in vegetable oils, is an important reducer of LDL (low density lipoproteins), which help to take cholesterol into the blood and cause atherosclerosis (buildup of plaque in the blood vessels) a prime cause of heart attacks Arachidonic acid is important in making eicosanoids, molecules which regulate and protect the body from invasion by microorganisms.

8. Waxes Waxes are simple lipids which are esters of long chain alcohols and fatty acids. Beeswax is a 30 C alcohol connected to a 16 C fatty acid Waxes are completely water resistant and make the coatings on leaves, skin, feathers, fur, and fruit. They can be used on floors and furniture for the same protecting quality.

9. Homework 16-a p. 409 CYU all p. 422 ff 1, 2, 3, 5, 7, 8, 12, 14

10. Reactions of Lipids Iodine number�iodine has a great affinity for double bonds in fatty acids. The amount which can be absorbed is called the iodine number. A reading over 70 indicates a great deal of unsaturation, less than 70 is very little or complete saturation Hydrogenation�hydrogen can be added to unsaturated fats to make them saturated and therefore more solid. This is done to make margarine and vegetable shortening. Rancidity�forming bad odor and taste from fats by hydrolysis and oxidation. Hydrolysis splits the glyceride link, oxidation breaks up the fatty acid at the double bonds, making short acids and aldehydes. To stop this, antioxidants like BHA, BHT, and vitamin E are added.

11. Examples Iodine number: Hydrolysis: Oxidation:

12. Saponification When hydrolysis happens due to a strong base, saponification happens, just as in esters before. In this case, three soap molecules are made: These soaps are hard or soft depending on the amount of unsaturation in the carbon chains.

13. Action of Soap How do soaps work? With a polar head (the sodium/carboxyl portion), soap is soluble in water. The long nonpolar tail allows the soap to attach to grease particles and create a micelle, a �bubble� of soap molecules surrounding the grease. The micelles carry away the grease and dirt with them in the rinse water

14. Hard Water Water containing acid, Ca+2, Mg+2, Fe+2, or Fe+3 will react with the soap to form �scum�. To stop this, those ions can be removed through softening or by using detergents. Detergents have a sulfate head rather than a carboxyl, and are not affected by the hard water ions or by acid.

15. Homework 16b p. 414 CYU all p 423 ff 15, 17, 20, 22, 23, 24

16. Compound Lipids Phospholipids�lipids which contain a phosphate group instead of on of the fatty acids on a glycerol X can be several different compounds Phospholipids are important in forming cell membranes and in transporting other lipids in the body. Phosphatidyl choline is one which the body uses in the liver, and is used in industry to make candy and medicine quaternary ammonium salt X= choline

17. Sphingolipids If instead of glycerol, another alcohol with two links, sphingosine, is used, sphingolipids are formed. These have one phosphate and one fatty acid If X is choline, as above, this would be sphingomyelin, a covering for nerve fibers

18. Glycolipids Instead of phosphate, sugar goups could be attached to either a glycerol or sphingosine to make a glycolipid. The usual sugar is galactose, but may be glucose Glycolipids are commonly found in nerve coverings

19. Non-Saponifiable Lipids Steroids�any molecule with the four ring structure: Sterols�steroid alcohols such as cholesterol. Cholesterol is formed from acetyl coenzyme A in the liver and makes part of cell membranes. Some important chemicals made from cholestrerol are bile acids, steroid hormones, and vitamin D. Too much cholesterol can build up in the arteries as mentioned before. LDL brings cholesterol into the blood, where it can build up, HDL removes it, so that a good diet would be one which encourages HDL and limits LDL.

20. Lipids in the Body The primary site of lipids in the body is in cell membranes. Due to the polar-nonpolar nature of lipids, the cell membrane is often a bi-layer structure, with the non-polar parts inward. Membranes throughout the body are of different percent compositions, depending on what they need to do. Since nerves must be kept from too much water, nerve coatings are around 70% lipid. The nuclear membrane, which must allow fluids to pass easily, is only about 40%.

21. Homework 16c p. 420 CYU all p. 424 ff 25, 29, 31, 32, 35, 39