Lipids of Physiologic Significance

1. Lipids of Physiologic Significance

2. The lipids are a heterogeneous group of compounds, including fats, oils, steroids, waxes, and related compounds, which are related more by their physical than by their chemical properties. • They have the common property of being (1) relatively insoluble in water and (2) soluble in nonpolar solvents such as ether and chloroform.

3. Functions • They are important energy source • Transporter of the fat-soluble vitamins • serves as a thermal insulator in the subcutaneous tissues and around certain organs. • Nonpolar lipids act as electrical insulators

4. Cont. • Combinations of lipid and protein occurringboth in the cell membrane and in the mitochondria, • Knowledge of lipid biochemistry is necessary in understanding many important biomedical areas, eg, obesity, diabetes mellitus, atherosclerosis,

5. Classification • Three classes • Simple lipid • Compound lipid • Derived lipid

6. Simple lipids: defined as Esters of fatty acids with various alcohols . Tow classes: a. Fats: Esters of fatty acids with glycerol. Oils are fats in the liquid state. b. Waxes: Esters of fatty acids with higher molecular weight alcohols.

7. 2.Complex lipids: Esters of fatty acids containing groups in addition to an alcohol and a fatty acid. a. Phospholipids: Lipids containing, in addition to fatty acids and an alcohol, a phosphate group+ nitrogen containing bases • in glycerophospholipidsthe alcohol is glycerol • and in sphingophospholipids the alcohol is sphingosine.

8. b. Glycolipids (glycosphingolipids): Lipids containing a fatty acid, sphingosine, and carbohydrate. c. Other complex lipids: Lipids such as sulfolipidsand aminolipids. Lipoproteins

9. 3. Derived lipids: These include fattyacids, glycerol, steroids, other alcohols, fatty aldehydes, and ketone bodies, lipid-soluble vitamins, and hormones.

10. FATTY ACIDS • ARE ALIPHATIC CARBOXYLIC ACIDS • occur mainly as esters in natural fats and oils but do occur in the un esterified form as free fatty acids, a transport form found in the plasma. • Fatty acids that occur in natural fats are usually straight-chain derivatives • containing an even number of carbon atoms. • The chain may be saturated (containing no double bonds) or • unsaturated (containing one or more double

11. Classification of unsaturated fatty acids • Fatty acids may be further subdivided as follows: (1) Monounsaturated ( monoenoic) acids, containing one double bond. (2) Polyunsaturated ( polyenoic) acids, containing two or more double bonds. (3) Eicosanoids: These compounds, derived from eicosa- (20-carbon) polyenoicfattyacids, comprise the prostanoids, leukotrienes (LTs), and lipoxins (LXs). • Prostanoids include prostaglandins (PGs), prostacyclins (PGIs), and thromboxanes (TXs)

12. nomenclature • saturated acids end in -anoic, eg, octanoic acid • unsaturated acids with double bonds end in -enoic, eg, octadecenoic acid (oleic acid). • Most important fatty acid in animal are palmetic 16C atom ,stearic 18C atom

13. Carbon atoms are numbered from the carboxyl carbon (carbon No. 1). • The carbon atoms adjacent to the carboxyl carbon (Nos. 2, 3, and 4) are also known as the α, β, and γ carbons, respectively, and the terminal methyl carbon is known as the ω or n-carbon.

14. Various conventions use ∆ for indicating the number and position of the double bonds ; eg,∆9 indicates a double bond between carbons 9 and 10 of the fatty acid. • Animals can not synthesize double bond beyond C9

15. So fatty acid having a double bond beyond C 9 are known as essential fatty acid eg: • Linoleic 2 double bond at C9&C12 • Linolenic 3 double bond at C9,C12 &C15

16. TRIACYLGLYCEROLS (TRIGLYCERIDES)TAG • Are the main storage form of lipid in animaltriacylglycerols are esters of glycerol and three fatty acids. • Mono- and diacylglycerols wherein one or two fatty acids are esterified with glycerol are also found in the tissues.

18. PHOSPHOLIPIDS • They are the main lipid constituents of membranes • Consist of alcohol glycerol +2fatty acid +phosphate group +nitrogen base

19. Phosphatidylcholines (Lecithins) • Phosphoacylglycerols containing choline • are the most abundant phospholipids of the cell membrane • represent a large proportion of the body’s • store of choline. • Choline is important in nervous transmission, as acetylcholine

21. Dipalmitoyl lecithin • it is a surfactant preventing adherence, due to surface tension, of the inner surfaces of the lungs. • Its absence from the lungs of premature infants causes respiratory distress syndrome.

22. Phosphatidylethanolamine (cephalin) • and phosphatidylserine found in most tissues differ from phosphatidylcholine only in that ethanolamine or serine, respectively, replaces choline

23. phosphatidylserine

24. Phosphatidylethanolamine

25. Phosphatidylinositol • Phosphatidylinositol 4,5-bisphosphate is an important constituent of cell membrane phospholipids • upon stimulation by a suitable hormone it is cleaved into diacylglycerol and inositoltrisphosphate, both of which act as internal signals or second messengers.

27. Cardiolipin • Is a Major Lipidof Mitochondrial Membranes

28. Cardiolipin

29. Plasmalogens • These compounds constitute as much as 10% of the phospholipids of brain and muscle. • Structurally, the plasmalogens resemble phosphatidylethanolamine but possess an ether link on the carbon -1

30. Sphingolipid • Sphingomyelinsare found in large quantities in brain and nerve tissue. • On hydrolysis, the sphingomyelins yield a fatty acid, phosphoric acid, choline, and a complex amino alcohol, sphingosine • Sphingosine plus fatty acid is known as ceramide,

32. GLYCOLIPIDS (GLYCOSPHINGOLIPIDS) • Glycolipids are widely distributed in every tissue of the body, particularly in nervous tissue such as brain. • They occur particularly in the outer leaflet of the plasma membrane, where they contribute to cell surface carbohydrates.

33. The major glycolipids found in animal tissues are glycosphingolipidseg 1- Galactosylceramideis a major glycosphingolipid of brain and other nervous tissue. 2-Glucosylceramideis glycosphingolipid of extraneural tissues 3-Gangliosides derived from glucosylceramide that contain in addition one or more molecules of a sialic acid.

35. Steroids • STEROIDS play many physiologically important role • All of the steroids have a similar cyclic nucleus consist 0f 3 cyclohexane rings (A, B, and C) to which a cyclopentane ring (D) is attached. • The carbon positions on the steroid nucleus are numbered as shown

37. Cholesterol, an amphipathic lipid, is an important component of membranes. • It is the parent molecule from which all other steroids in the body are synthesized including: • Sex hormones • D vitamins • Bile acids its association with atherosclerosis.

38. 14:0 Myristic acid CH3(CH2)12COOH O • 16:0 Palmitic acid CH3(CH2)14COOH • 16:1D9Palmitoleic acid CH3(CH2)5C=C(CH2)7COOH • 18:0 Stearic acid CH3(CH2)16COOH • 18:1D9 Oleic acid CH3(CH2)7C=C(CH2)7COOH • 18:2D9,12Linoleicaci CH3(CH2)4C=CCH2C=C(CH2)7COOH Essential fatty acid • 18:3D9,12,15Linolenic CH3CH2C=CCH2C=CCH2C=C(CH2)7COOH Essential fatty acid • 20:4D5,8,11,14Arachidonic acid CH3(CH2)3(CH2C=C)4(CH2)3COOH Precursor for