Structure of lipids

1. Structure of lipids Pavla Balínová

2. Lipids Lipids are a large and heterogenous group of substances of biological origin. They are easily dissolved in organic solvents but they are insoluble or poorly soluble in water. Biological roles of lipids: ●lipids are important source of energy – they serve as metabolic fuel (ATP production)‏ ● amphipathic lipids are building blocks of cellular membranes ● lipids are excellent insulators (subcutaneous tissue and around various organs)‏ •special tasks – signaling functions, hormones,....

3. Classification of lipids I. Simple lipids ● Triacylglycerols (fats)‏ ● Waxes II. Complex lipids ●Glycerophospholipids ●Sphingophospholipids ●Glycolipids III. Isoprenoids and steroids ● Isoprenoids: vitamins A, D, E, K ● Steroids: sterols, bile acids, steroid hormones Figure is found on http://en.wikipedia.org/wiki/Triacylglycerol

4. Structural components of lipids a) a) a) b) • alcohols • glycerol • sfingosine (unsaturated C18 aminoalcohol) • cholesterol • inositol • long chain carboxylic acids (= fatty acids) The figures were adopted from http://en.wikipedia.org

5. Fatty acids (FA)‏ • are carboxylic acids with unbranched hydrocarbon chains of 4 – 24 C atoms • in fats or membrane lipids they are esterified with alcohols (glycerol, sphingosine)‏ • free fatty acids (FFAs) = unesterified forms of FA • in higher plants and animals, unbranched, longchain FA with either 16 or 18 C atoms are the most common (palmitic and stearic acid)‏ • the number of C atoms in the longer, natural FA is always even(synthesis from acetyl residues)

6. The figure was adopted from: J.Koolman, K.H.Röhm / Color Atlas of Biochemistry, 2nd edition

7. Saturated FA • Palmitic acid CH3-(CH2)14-COOH • Stearic acid CH3-(CH2)16-COOHUnsaturated FA • contain 1 or more double bond(s)‏ • Oleic acid 18:1, position 9 • Linoleic acid 18:2, positions 9, 12 • Linolenic acid 18:3, positions 9, 12, 15 • Arachidonic acid 20:4, positions 5, 8, 11, 14 • Greek letters (ω) are also commonly used: • ω = the last C, ω-3 = the third last C

8. Essential FA • are FA that have to be supplied in the diet Polyunsaturated FA: • Linoleic acid ω-6 • Linolenicacid ω-3 • Arachidonic acid ω-6 Human organism is not able to introduce double bonds into the end sections of FA (after C-9)‏.

9. Triacylglycerols (neutral fats)‏ ester bond • are esters of glycerol and 3 fatty acids ester bond Diacylglycerol = glycerol + 2 FA Monoacylglycerol = glycerol + 1 FA Lipases = enzymes that hydrolyze ester bonds

10. Complex lipids The figure was adopted from: J.Koolman, K.H.Röhm / Color Atlas of Biochemistry, 2nd edition, Thieme 2005

11. Complex lipids A) PHOSPHOLIPIDS ● glycerophospholipids ● sphingophospholipids B) GLYCOLIPIDS ● sphingolipids

12. Glycerophospholipids = glycerol + 2 FA + phosphate group + hydrophilic compound • phosphatidic acid + polar compound (ethanolamine, inositol, choline, serine) • are the main constituents of biological membranes Phosphatidylethanolamine (cephalin)‏ Phophatidylinositol Phosphatidylcholine (lecithin)‏ choline

13. Sphingophospholipids = sphingosine + FA + phosphate residue + amino alcohol or sugar alcohol - are found in large quantities in the membranes of nerve cells Ceramide = sphingosine + fatty acid (amide bond) Sphingomyelin(myelin sheaths) sphingosine

14. Glycolipids = sphingosine + FA + sugar or oligosaccharide residue The phosphate group is absent. Gangliosides= ceramide + oligosaccharide unit Cerebrosides = ceramide + Gal (Glc) Galactocerebroside galactose

15. Isoprenoids and steroids • isoprenoids (terpenes) are derived from an isoprene(2-methyl-1,3-butadiene)‏ • isoprene metabolism in plants is very complex – synthesis of many types of aromatic substances (menthol, camphor, citronellal) • activated isoprene can be used in synthesis of fat-soluble vitamins (A, D, E, K) • isoprene is a precursor in synthesis of cholesterol (→ steroid hormones, bile acids)‏

16. Examples of terpenes menthol (C10) phytol (C 20) squalene (C 30) -carotene (C40) The figures were adopted from http://en.wikipedia.org

17. Steroids - overview Sterols are steroid alcohols • -OH group in C-3 position and one or more double bonds • cholesterol, ergosterol (plants)‏ Bile acids are synthesized from cholesterol in the liver • cholic acid, chenodeoxycholic acid, lithocholic acid, deoxycholic acid Steroid hormonesregulate metabolism, growth and reproduction • progesterone, estrogene, testosterone, aldosterone, cortisol, calcitriol

18. Sterane The figure is found athttp://courses.cm.utexas.edu/archive/Spring2002/CH339K/ Robertus/overheads-2/ch11_cholesterol.jpg

19. Cholesterol „free“ cholesterol Cholesterol is a constituent of cellular membranes and it is present in all animal tissues. Cholesterol esters with FA are insoluble in the water. Lipoproteins (LDL, HDL) are transporters of cholesterol in blood. Figures were assumed from a book T. M. Devlin et al.: Textbook of Biochemistry With Clinical Correlations, 4th ed., Wiley‑Liss, Inc., New York, 1997.

20. Steroid hormones • cholesterol is a metabolic precursor of all steroid hormones in human body • number of C atoms is changing during synthesis of hormones: from 27 to 21, 19 or 18 • glucocorticoids (21 C) ●mineralocorticoids (21 C) ● sex hormones (progesterone 21 C, testosterone 19 C, estrogene 18 C)

21. Steroid hormones Figure was adopted from: J.Koolman, K.H.Röhm / Color Atlas of Biochemistry, 2nd edition, Thieme 2005

22. are formed from cholesterol in the liver and they are excreted into a bile primary bile acids: cholic and chenodeoxycholic acid ● secondary bile acids: deoxycholic and lithocholic acid Function: emulsification of lipids in intestine → digestion and resorption Bile acids Figure was assumed from book T. M. Devlin et al.: Textbook of Biochemistry With Clinical Correlations, 4th ed., Wiley‑Liss, Inc., New York, 1997.