Chapter 21: Lipids

1. Chapter 21: Lipids

2. Chapter 21: Lipids • Triglyceride: A triester of glycerol with three fatty acids. • Hydrophobic (most of the molecule is non-polar) • Two or three different fatty acid components are present • The Fatty acids: • Are unbranched carboxylic acids • 10 to 20 carbons long, even number of carbons • Cis-isomer

3. Chapter 21: Lipids Hardening: The reduction of some or all of the carbon-carbon double bonds of an unsaturated triglyceride using H2/transition metal catalyst, which converts a liquid triglyceride to a semisolid. • In practice, the degree of hardening is carefully controlled to produce fats of a desired consistency. • The resulting fats are sold for kitchen use (Crisco, Spry, Dexo, and others). • Margarine and other butter substitutes are produced by partial hydrogenation of polyunsaturated oils derived from corn, cottonseed, peanut, and soybean oils. • The hardening process is the source of trans fatty acids

4. Chapter 21: Lipids Saponification: the base-promoted hydrolysis of fats and oils in aqueous NaOH and produces glycerol and a mixture of fatty acid salts called soaps.

5. Chapter 21: Lipids Phospholipids and Glycolipids

6. Chapter 21: Lipids Complex lipids form the membranes around cells and around small structures within cells. In aqueous solution, complex lipids spontaneously form into a lipid bilayer, with a back-to-back arrangement of lipid monolayers. • Polar (hydrophilic) head groups are in contact with the aqueous environment. • Nonpolar (hydrophobic) tails are buried within the bilayer and shielded from the aqueous environment. • The major force driving the formation of lipid bilayers is hydrophobic interaction. • The arrangement of hydrocarbon tails in the interior can be rigid (if rich in saturated fatty acids) or fluid (if rich in unsaturated fatty acids).

7. Chapter 21: Lipids

8. Chapter 21: Lipids Glycerolphospholipids X = Alcohol R1 = Fatty acid tail (saturated or unsaturated) R2 = Fatty acid tail (this one is always unsaturated)

9. Chapter 21: Lipids X = Choline If the other alcohol is choline, the glycerophospholipid is called a phosphatidylcholine (common name lecithin).

10. Chapter 21: Lipids X = ethanolamine or serine If the other alcohol is ethanolamine or serine, the glycerophospholipid is called a cephalin.

11. Chapter 21: Lipids Sphingolipids: Contain sphingosine instead of glycerol, from which this class of compounds in named. The sphingolipid myelin is found in the coatings of nerve axons.

12. Chapter 21: Lipids • Glycolipid: a complex lipid that contains carbohydrates and ceramides. • The carbohydrate is either glucose or galactose. • The cerebrosides are ceramide mono- or oligosaccharides. • The following is a glucocerebroside.

13. Chapter 21: Lipids Steroids: A group of plant and animal lipids that contain this tetracyclic ring structure Cholesterol is the most abundant steroid in the human body, and also the most important. • It is a component in plasma membranes in all animal cells. • It is the precursor of all steroid hormones and bile acids.

14. Chapter 21: Lipids

15. Steroid Hormones • Male sex hormones • Synthesized in the testes from cholesterol. • Responsible for the development of male secondary sex characteristics.

16. Steroid Hormones Among the synthetic anabolic steroids are:

17. Steroid Hormones Female sex hormones • Synthesized in the ovaries from progesterone. • Responsible for the development of female secondary sex characteristics and control of the menstrual cycle.

18. Steroid Hormones • Progesterone-like analogs are used in oral contraceptives:

19. Glucocorticoid Hormones • Glucocorticoid hormones • Synthesized in the adrenal cortex. • Regulate metabolism of carbohydrates. • Decrease inflammation. • Involved in the reaction to stress.

20. Bile Salts Bile salts are oxidation products of cholesterol. • Synthesized in the liver, stored in the gallbladder, and secreted into the intestine where they emulsify dietary fats and aid in their absorption and digestion.

21. Chapter 21: Lipids Lipoproteins: Carriers of cholesterol.

22. Chapter 21: Lipids Lipoproteins

23. Chapter 21: Lipids • Chylomicrons carry triglycerides (fat) from the intestines to the liver, skeletal muscle, and to adipose tissue. • Very low density lipoproteins (VLDL) carry (newly synthesised) triacylglycerol from the liver to adipose tissue. • Intermediate density lipoproteins (IDL) are intermediate between VLDL and LDL. They are not usually detectable in the blood. • Low density lipoproteins (LDL) carry cholesterol from the liver to cells of the body. LDLs are sometimes referred to as the "bad cholesterol" lipoprotein. • High density lipoproteins (HDL) collect cholesterol from the body's tissues, and bring it back to the liver. HDLs are sometimes referred to as the "good cholesterol" lipoprotein.

24. Chapter 21: Lipids LDL: • LDL Normal plasma levels are 175 mg/100 mL. • If there are sufficient LDL receptors on the surface of cells, LDL is removed from circulation and its concentration in blood plasma drops. • In the disease called famelial hypercholesterolemia, there are not enough LDL receptors and plasma levels of cholesterol may be as high as 680 mg/100 mL. • The commonly used statin drugs inhibit the synthesis of cholesterol by blocking HMG-CoAreductase