UNIT 5. LIPIDS

1. UNIT 5. LIPIDS

2. OUTLINE 5.1. Introduction. 5.2. Fatty acids. 5.3. Eicosanoids. 5.4. Triacylglycerols = Triglycerides. 5.5. Waxes. 5.6. Membrane lipids: glycerophospholipids and sphingolipids. 5.7. Isoprenoids (and steroids) 5.8. Lipoproteins.

3. 5.1. INTRODUCTION: • Organic molecules highly hydrophobic and water insoluble. • Biological roles: • - Energy reserve (i.e. triacylglicerols). • - Structural component of the biological membranes • (i.e. phospholipids). • - Protection (i.e. wax). • - Biochemical signals, cofactor or pigments • Lipid Classification: • - Fatty acids. - Phospholipids. • - Eicosanoids. - Sphingolipids. • - Triacylglicerols. - Isoprenoids. • - Waxes. - Conjugated lipids.

4. 5.2. FATTY ACIDS: • Carboxylic acids with long-chain hydrocarbon side groups. • They can be branched and saturated, unsaturated or polyunsaturated (contain two or more double bonds). • The double bonds tend to occur at every third carbon atom (not conjugated). • Ionizated at physiological pH. • Usually, they are in the free, uncomplexed state. conjugated Not conjugated

5. 5.2. FATTY ACIDS:

6. 5.2. FATTY ACIDS: • Fatty acid double bonds almost always have the cis configuration. Polar group Hydrophobic chain Unsaturated acid: Linoleic acid Saturated fatty acid: Stearic acid

7. 5.2. FATTY ACIDS: • Properties: •  Higher unsaturated grade: higher fluidity. •  Higher unsaturated grade (same chain length): lower melting point.

8. 5.3. EICOSANOIDS: • They are derived from arachidonic acid, 20:4(5,8,11,14). • Types: •  Prostaglandins(they act as local hormones): they are involved in • - The production of pain and fever • - Inflammation processes • - Increase of the body temperature • - Regulation of blood pressure and blood coagulation. • - Control of the Ionic transport. • - Dream induction

9. 5.3. EICOSANOIDS: Thromboxanes (found within platelets): Stimulate vasoconstriction and platelet aggregation.  Leukotrienes (present within leukocytes): Involved in: - Oedema production. - Vasoconstriction. - Bronchi constriction - Anaphylactic processes.

10. 5.4. TRIACYLGLICEROLS: • Glycerol esterified with three fatty acids. Monoacylglicerols and diacylglicerols are metabolic intermediates. • Major energy reserve (stored in anhydrous form). • Types: Simple triacylglicerols (i.e. tristearoylglycerol(= tristearin); trioleoylglycerol (=triolein). Mixed triacylglicerols (i.e. 1-stearoyl, 2-linoleoyl, 3-palmitoyl glycerol). • Highly hydrophobic. • Adipocytes and adipose tissue. • Thermal insulation (important for warm-blooded aquatic animals).

11. 5.4. TRIACYLGLICEROLS: • Provide about six times the metabolic energy of an equal weight of hydrated glycogen. • They are hydrolysed by lipases or alkali (saponification): triestearina trioleina G L Y C E R O L G L Y C E R O L + Fatty acid + Na+ Fatty acid NaOH or KOH + Fatty acid + Na+ Fatty acid + Fatty acid Fatty acid + Na+ Soap Chemical composition of three eatable fats.

12. 5.5. WAXES: • Esters of long-chain monohydroxylic alcohols (16-30 C) with long-chain fatty acids (14-36 C) (saturated or unsaturated) • Properties: • - Energy reserve (plancton). - Water-repellant surfaces (i.e. animals skin, leaves of certain plants, bird feathers). - Highly hydrophobic. - Several industrial uses (lotions, cosmetics, etc.). Triacontanylpalmitate, major component of the bee wax.

13. Amphipathic lipids • 5.6. MEMBRANE LIPIDS:

14. 5.6. MEMBRANE LIPIDS: GLYCEROPHOSPHOLIPIDS: • 1,2-diacylglycerol that has a phosphate group esterified at the carbon atom 3 of the glycerol backbone. The phosphate group is linked to a highly polar or charged group (X). • Usually they contain a saturated fatty acid (C16 or C18)C1-linked and an unsaturated fatty acid (C16-C20) C2-linked. • Amphipathic molecules. • They are derived from phosphatidic acid. Glycerophopholipids backbone structure

15. 5.6. MEMBRANE LIPIDS: GLYCEROPHOSPHOLIPIDS: (Cefalina) (Lecitina) Phosphatidylcholine

16. choline • 5.6. MEMBRANE LIPIDS: GLYCEROPHOSPHOLIPIDS: • Some phospholipids contain an alkyl group ether linked. Plasmalogen (heart muscle) Platelet activating factor: major mediator of hypersensivity, acute inflammatory reactions, allergic responses and anaphylactic shock.

17. Polar group • 5.6. MEMBRANE LIPIDS: SPHINGOLIPIDS • One polar group and to unpolar chains (glycerol is not present) • They contain the amino alcohol sphingosine, one fatty acid (long chain) and a polar group (alcohol or sugar)

18. 5.6. MEMBRANE LIPIDS: SPHINGOLIPIDS Phospholipids Glycolipids

19. 5.6. MEMBRANE LIPIDS: SPHINGOLIPIDS • Cerebrosides and globosides (ceramide oligosaccharides) are neutral glycolipids. Gangliosides contain N-acetylneuraminic acid (sialic acid), with negative charge at pH 7.

20. 5.6. MEMBRANE LIPIDS: SPHINGOLIPIDS • The carbohydrate present in several sphingolipids define the human being blood groups ( A, B and 0).

21. 5.7. ISOPRENOIDS: • They contain isoprene units (5 C). • They precursor for the synthesis is isopentenylpyrophosphate . • The isoprenoids are grouped into terpenes and steriods.

22. 5.7. ISOPRENOIDS: TERPENES • Classification in the base of the number of isoprene units

23. 5.7. ISOPRENOIDS: TERPENES • Linear or cyclic structures. • Present in plants, fungi and bacteria. • Pigments, molecular signalling (hormones and pheromones) and defence agents. • Plant oils belong to this groups (aromas and flavours). • They are precursor for fat-soluble vitamins synthesis.

24. 5.7. ISOPRENOIDS: TERPENES • Fat-soluble vitamins: they cannot be synthesised by human beings (diet). • They are dissolved as fats and oils. Vitamin A (retinol): • - Hormone and main pigment involved in vision. • - It is a carotenoid. • Vitamin D: • - It is derived from cholesterol. • - It increases the concentration of Ca2+ in physiological serum • Vitamin E (tocopherols): • - Biological antioxidant, It avoid food degradation. • - Prevent oxidation of the membrane lipids.

25. 5.7. ISOPRENOIDS: TERPENES • Vitamin K: • - Blood clotting. • Ubiquinones and plastoquinones: • - Lipophilic electron transporters (redox reactions). Vitamin E Vitamin K1 Ubiquinone

26. 5.7. ISOPRENOIDS: STERIODS: • Membrane lipids in eukaryotic cells. • They are derived from triterpenes containing 4 rings: phenathrene nucleus (3 rings containing 6 C), and a pentane ring (5 C): Cyclopentanoperhydrophenanthrene. • They are classified on the base of the number and position of the double bonds, location of the radicals, etc.

27. 5.7. ISOPRENOIDS: STERIODS: Cholesterol: Main steriod in animals (cellular membranes) It is amphipathic. It is the precursor in the synthesis of many steriods such as hormones, vitamin D, bile acids

28. 5.7. ISOPRENOIDS: STERIODS: Bile acids: they act as detergents in gut. They are more soluble than cholesterol. Steroid hormones: they promote metabolism and gene expression changes. Types: - Glucocorticoids: i.e: cortisol: involved in proteins, lipids and carbohydrates metabolism. - Aldosterone and mineralocorticoids:, they regulate water and salt excretion (kidneys). - Androgens and estrogens: sexual development.

29. 5.7. ISOPRENOIDS: STERIODS:

30. 5.8. LIPOPROTEINS: • Molecular complexes in blood plasma of mammals. • They facilitate lipids transfer between tissues (triacylglycerols, phospholipids and cholesterol). • Apolipoproteins or apoproteins are synthesised in the liver. • They have different density and lipids/proteins ratio.

31. 5.8. LIPOPROTEINS: - Chylomicrons: extremely low density. They transport triacylglycerols and cholesterol esters (food) from gut to adipose tissue and muscles. - Very-low-density lipoproteins (VLDL): they transfer lipids (triacylglycerols) to the tissues to be used for energy. - Low-density lipoproteins (LDL): they transport cholesterol and its esters to the tissues. - High-density lipoproteins (HDL): Rich in cholesterol but poor in triacyglycerol (they promote the excretion of the excess of cholesterol).

32. 5.8. LIPOPROTEINS: