Biological role of lipids

Transcription

1 Lipids

2 Lipids Organic compounds present in living organisms, insoluble in water but able to be extracted by organic solvents such as: chloroform, acetone, benzene. Extraction = the action of taking out something, the process of obtaining something from a mixture or compound by chemical, physical or mechanical means 2

3 Biological role of lipids as a building material for all membrane-like structures in cells (phospholipids, cholesterol, glycolipids) have a decisive role in dynamic processes of cell membrane; influence fluidity, asymmetry, permeability, enzymatic activity and receptor properties (phospholipids, cholesterol, fatty acids) steroid hormon precursor (cholesterol) and tissue hormons (fatty acids) substrate for fatty acids synthesis and some vitamins take part in immunological processes (eicosanoids) [eicosanoids are signaling molecules made by oxidation of twenty-carbon essential fatty acids] 3

4 LIPID categories (according to Bloor) Simple (esters of fatty acids with alcohols) Complex (esters of fatty acids with alcohols containing additional functional groups) Precursors and lipid derivatives: fatty acids sterols (e.g. cholesterol) vitamins soluble in fats, hormones acylglycerols waxes Other complex lipids: phospholipids: glycerophospholipids sphingolipids (sphingophosfolipids) glycolipids: cerebrosides gangliosides sulpholipids aminolipids lipoproteins 4

5 FATTY ACIDS STRUCTURE AND PROPERTIES 1. Fatty acids are monocarboxylic acids with hydrocarbon chains of different amount of carbon atoms: 4 to 30. Depends on carbon amount, they are: 1. short-chain fatty acids ( < 6 atoms C) 2. medium-chain fatty acids ( 6 14 atoms C) 3. long-chain fatty acids ( > 14 atoms C) 2. Fatty acids are amphipathic: hydrocarbon chain has hydrophobic character carboxyl group has polar character 5

6 FATTY ACIDS FUNCTIONALITY structural role in cell membranes energy storage in adipocytes (cell which store synthesized fats) covalent modification of proteins in protein play a role as a hydrophobic anchor energy material derivatives of 20-carbon fatty acids are hormones 6

7 FATTY ACIDS STRUCTURE and PROPERTIES Saturated fatty acids contain over 10 carbon atoms in chain are insoluble in water melting point increases with length of the chain are solids Unsaturated fatty acids: in room temperature usually are liquids at least one double bond. Salts of fatty acids and alkali metals are well soluble in water but magnesium and calcium salts are almost insoluble. 7

8 FATTY ACIDS - STRUCTURE and PROPERTIES Presence of a double bond allows unsaturated fatty acids to posses two stereo-isomeric structures : cis and trans Oleic acid Elaidic acid 6 8

9 FATTY ACIDS Nomenclature Common names of fatty acids in most cases are associated with the source of their discovery Systematic names are composed of Greek numbers with following endings: - anoic for saturated acids - enoic for unsaturated acids Octadecanoic acid 9,12 octadecadienoic acid Stearic acid Linoleic acid 9

10 FATTY ACIDS Nomenclature Systematic names are from Greek numbers location of unsaturated, double bond is indicated by D number of carbon atom participating in double bond is counted starting from carbon atom at carboxylic group letters n or w indicate double bond location, starting from the methyl group. w Fatty acid with cis D-9 bond 10

11 UNSATURATED FATTY ACIDS Common name Systematic name Abbreviated name Chemical structure Oleic 9 octadecenoic 18:1 D 9 18:1 (n-9) Eicosenoic 9 - eicosenoic 20:1 D 9 Erucic 13 - docosenoic 22:1 D 13 Linoleic Linolenic Arachidonic 9,12 - octadecadienoic 9,12,15 - octadecatrienoic 5,8,11,14 - eicosatetraenoic 18:2 D 9,12 18:2 (n-6) 18:3 D 9,12,15, 18:3 (n-3) 20:4 D 5,8,11,14, 20:4 (n-6) CH 3 (CH 2 ) 7 CH=CH(CH 2 ) 7 COO H CH 3 (CH 2 ) 9 CH=CH(CH 2 ) 7 COO H CH 3 (CH 2 ) 7 CH=CH(CH 2 ) 11 COO H CH 3 (CH 2 ) 4 (CH=CHCH 2 ) 2 (CH 2 ) 6 COOH CH 3 CH 2 (CH=CHCH 2 ) 3 (CH 2 ) 6 COOH CH 3 (CH 2 ) 4 (CH=CHCH 2 ) 4 (CH 2 ) 2 COOH 11

12 FATTY ACIDS NECESSARY UNSATURATED FATTY ACIDS, (vitamin F) There are 3 families of these acids: omega-3, omega-6 and omega-9 Human organism is able to place double bond only in position 9 counting from methyl group. Precursors of omega acids with double bonds between position 3 and 6 must be delivered to organism with food. Sources of unsaturated fatty acids : - vegetable oils, soy, corn oil - animal phospholipids Polyunsaturated fatty acids from omega family, with 5 and 6 double bonds are in large quantities in fish oils. 12

13 Acyl Fats (acylglyceroles) Because of their chemical structure they belong to esters: - alcohol component glycerol - acid component monocarboxylic higher fatty acids Most often they are mixtures of triglycerols of various fatty acids. Glycerol H 2 C OH C 1 a sn-1 HO C H C 2 b sn-2 H 2 C OH C 3 a sn-3 In acylglycerols secondary hydroxyl group is located on the left side of carbon atom 13

14 Acyl Fats (acylglyceroles) Glycerol Triacylglycerol O H 2 C OH HO C H H 2 C OH O H 2 C O C R 1 R 2 C O C H H 2 C O C R 3 O 14

15 Glycerophospholipids Phosphatidic acid Phosphatidylcholine (lecithin) phosphatidic acid + HO CH2 CH2 N(CH3)3 (choline) Glycerophospholipids contain four components: glycerol two acyl groups connected by ester bond (with C1and C2 from glycerol) orthophosphate connected by ester group (with C3 from glycerol) other alcohol (choline, ethanolamine, serine, glycerol), connected with -OH group of orthophosphate 15

16 Phospholipids Phosphatidic acid + HO CH 2 CH 2 N(CH + 3 ) 3 (choline) R` - palmitic acid R oleic acid Phosphatidylcholine (lecithin) Phosphatidic acid + ethanolamine Phosphatidylethanolamine 16

17 Sphingophospholipids Are composed of: sphingosine long-chain, monounsaturated dihydroxyl aminoalcohol long chain fatty acid phosphate choline 17

18 Sphingophospholipids Sphingosine (amino alcohol) + unsaturated fatty acid Ceramide (N- acetylsphingosine) (sphingosine + fatty acid) cell membrane component + choline + H 3 PO 4 Sphingomyelin Sphingomyelin in very large quantities is present in the myelin sheaths of nerve fibers acting as good insulator of nerve tissue. Multiple sclerosis (MS) is a disease in which degradation of the myelin sheath is observed 18

19 Glycosphingolipids Contain: ceramide sugar molecule (one or more) galactosylceramide glucosylceramide (cerebroside) Both are present in brain 19

20 Gangliosides Glucosylceramide derivatives containing one or several groups of sialic acid Sialic acid Ganglioside G M1 20

21 Cholesterol cholesterol belongs to steroids and contains 6 isoprene units it s a precursor of all steroid hormones component of cell membranes 21

22 Synthesis of cholesterol squalene lanosterol sterane cholesterol 22

23 Sterane structure (1) C D A B cyklopentanoperhydrophenanthrene Structure: three rings of cyklohexane and one ring of cyklopenthane Component of: cholesterol steroid hormones bile acids 23

24 Sterane structure (2) 5- a- hydrogen 5-b- hydrogen trans cis 24

25 Sterane structure 5- a- hydrogen 5-b- hydrogen 25

26 Cholesterol Lack of hydrogen atom at C5, double bond in ring B Hydroxyl derivative of sterane hydroxyl group at carbon atom C3 26

27 Cholesterol exists in all cell membranes in mammals steroids representative it has a flat and stiff structure in cytoplasm present in esterified form it makes up 10% -15% of dry mass of brain excess of cholesterol accelerates the development of atherosclerotic lesions in blood vessels (LDL low density lipoprotein)) It is a substrate for synthesis of: bile acids, steroid hormones, vitamin D3 27

28 Bile acids synthesized from cholesterol in liver contain 1 to 3 hydroxyl groups attached to the ring contain carboxyl group in side chain are amphipatic (hydrophilic and hydrophobic) can decrease surface tension of water good emulsifier of consumed fat 28

29 Bile acids - Cholic acid 29

30 Steroid hormones progesteron it is a byproduct in synthesis of steroid hormones Is created in oxidation of 3-OH group to ketone group and isomerization of a double bond 30

31 Steroid hormones Cortisol increases decomposition of fats, decreases immunological, allergic and inflammation reactions it is formed in a process of progesterone hydroxylation 31

32 Steroid hormones Aldosteron prevents dehydration of organism. 32

33 Steroid hormones androgenes - Testosteron: responsible for characteristic features in male formed from progesterone, from which C20 i C21 are removed 33

34 Steroid hormones Estrogen- female sex hormone, it is formed in fat tissue, skin and liver 34

35 Arachidonic acid Eicosanoids - derivatives of polyunsaturated fatty acids with 20 carbon atoms Structural formula ,8,11,14-eicosatetraenoic acid Half-structural formula: CH 3 (CH 2 ) 4 CH=CHCH 2 CH=CHCH 2 CH=CHCH 2 CH=CH(CH 2 ) 3 COOH 35

36 Arachidonic acid synthesized from exogenous fatty acids precursor of several groups of compounds with strong and versatile biological meaning Its derivatives are part of cellular hormones concentration of free arachidonic acid in cell is usually very low it is one of phospholipid membrane component. 36

37 THE END 37