By: Dr Hadi Mozafari 1

Transcription

1 Biological lipids are a chemically diverse group of compounds, the common and defining feature of which is their insolubility in water. By: Dr Hadi Mozafari 1

2 Fats and oils are the principal stored forms of energy in many organisms. Phospholipids and sterols are major structural elements of biological membranes. Other roles as thermal insulation, electrical insulation, light absorbing pigments, hydrophobic anchors for proteins Emulsifying agents in the digestive tract, hormones, and intracellular messengers. 2

3 1. Simple lipids - Esterification of Glycerol & Fatty Acids (FA) - Waxes are composed from FA & Heavy Alcohol 2. Compound Lipids These are Simple lipid added to Chemical agents e.g. Phosphoric acid, carbohydrates and etc 3

4 Fatty acids are carboxylic acids with hydrocarbon chains ranging from 4 to 36 carbons long (C4 to C36). They are saturated or unsaturated. In some fatty acids, this chain is unbranched and fully saturated (contains no double bonds); in others the chain contains one or more double bonds 4

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7 The chain length and number of double bonds, separated by a colon; for example, the 16-carbon saturated palmitic acid is abbreviated 16:0, and the 18-carbon oleic acid, with one double bond, is 18:1 The positions of any double bonds are specified by superscript numbers following (delta); a 20-carbon fatty acid with one double bond between C-9 and C-I0 (C-1 being the carboxyl carbon) and another between C-12 and C-13 is designated 20:2( 9,12 ) The double bonds are separated by a methylene group. 7

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9 Cis & Trans isomerism: If the hydrogen atoms are on the same side of the double bonds of the carbon chain then it is said to be in cis configuration. If the hydrogen atoms are on the opposite side of the double bonds of the carbon chain, then it is said to be in trans configuration In nearly all naturally occurring unsaturated fatty acids, the double bonds are in the cis configuration. Trans fatty acids are produced by fermentation in the rumen of dairy animals and are obtained from dairy products, fried oils and meat. 9

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12 Fatty Acids & Nutrition Fatty acids (FA) types are effective on Cardio-Vascular Dis LDL & HDL Some findings: - Saturated FA substitution with Unsaturated FA led to LDL - PUFA in foods & Atherosclerosis - Trans FA & Atherosclerosis or Cancer Trans FA Sources: - Oil Hydrogenation - Dairy products & Meat - Fast Foods ω 6 / ω 3 Ratio must be about 4 or less 12

13 The physical properties of the fatty acids, and of compounds that contain them, are largely determined by the length and degree of unsaturation of the hydrocarbon chain. The nonpolar hydrocarbon, fewer double bonds or longer chain accounts for the poor solubility of fatty acids in water. The carboxylic acid group is polar (and ionized at neutral ph) and accounts for the slight solubility of short-chain fatty acids in water. 13

14 Melting points are strongly influenced by the length and degree of unsaturation of the hydrocarbon chain. At room temperature, the saturated fatty acids from 12:0 to 24:0 have a waxy consistency, whereas unsaturated fatty acids of these lengths are oily liquids. - Cell membrane has an unsaturated lipids - Storage lipids has a saturated lipids 14

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16 Fatty Acids energy production 16

17 Are Fatty Acid Esters of Glycerol, also referred to as triglycerides, fats, or neutral fats. Its composed of three fatty acids each in ester linkage with a single glycerol and occurs in Liver & Adipose Tissue TG Provides Stored Energy and Insulation Energy is produce by Lipolysis and led to FA & Glycerol production 17

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19 Because the polar hydroxyls of glycerol and the polar carboxylates of the fatty acids are bound in ester linkages, triacylglycerols are nonpolar, hydrophobic molecules, essentially insoluble in water Lipids have lower specific gravities than water, which explains why mixtures of oil and water have two phases: oil, with the lower specific gravity, floats on the aqueous phase Triacylglycerols are also stored as oils in the seeds of many types of plants Adipocytes and seeds contain lipases, enzymes that catalyze the hydrolysis of stored triacylglycerols 19

20 The central feature of biological membranes is a double layer of lipids, which acts as a barrier to the passage of polar molecules and ions. Membrane lipids are amphipathic: one end of the molecule is hydrophobic, the other hydrophilic. Their hydrophobic interactions with each other and their hydrophilic interactions with water direct their packing into sheets called membrane bilayers. 20

21 Also called phosphoglycerides, are membrane lipids in which two fatty acids are attached in ester linkage to the first and second carbons of glycerol, and a highly polar or charged group is attached through a phosphodiester linkage to the third carbon. 21

22 Phospholipids The polar alcohol may be negatively charged (as in phosphatidylinositol 4,5-bisphosphate), neutral (phosphatidylserine), or positively charged (phosphatidylcholine, phosphatidylethanolamine). In general, glycerophospholipids contain a C 16 or C 18 saturated fatty acid at C-1 and a C 18 to C 20 unsaturated fatty acid at C-2. 22

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24 1. Cardiolipin 24

25 2. Phosphatidylcholine 25

26 3. Phosphatidylethanolamine 4. Phosphatidylserine 26

27 5. Phosphatidylinositol 6. Lysophospholipid 27

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29 platelet-activating Factor (one ether lipid) is a potent molecular signal. It is released from leukocytes called basophils and stimulates platelet aggregation and the release of serotonin (a vasoconstrictor) from platelets. 29

30 8. Sphingolipids They have a polar head group and two nonpolar tails, but unlike glycerophospholipids, they contain no glycerol. They have a C 18 amino alcohol, named sphingosine Ceramide = Sphingosine + Fatty Acid - Ceramide is the structural parent of all sphingolipids. Two Example: - Sphingomyelin in myelin sheath of neural cell. It serve for Transmission of nerve messages - Glycolipids are located on external layer of membrane. It serve as antigen (blood group) 30

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32 There are three subclasses of sphingolipids, all derivatives of ceramide but differing in their head groups: 1.Sphingomyelins Contain phosphocholine as their polar head group 2. Neutral (uncharged) glycolipids Occur largely in the outer face of plasma membranes, have head groups with one or more sugars connected directly to the -OH at C-1 of the ceramide moiety; they do not contain phosphate. Those with galactose( in the plasma membranes of cells in neural tissue), and those with glucose in the plasma membranes of cells in nonneural tissues 3. Gangliosides Gangliosides are complex glycosphingolipids derived from glucosylceramide that contain in addition one or more molecules of a sialic acid. Neuraminic acid is the principal sialic acid found in human tissues. Gangliosides are also present in nervous tissues in high concentration, as a receptors and etc. 32

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34 Most cells continually degrade and replace their membrane lipids. For each hydrolyzable bond in a glycerophospholipid, there is a specific hydrolytic enzyme in the lysosome. Phospholipases (PL) remove one of the two fatty acids, producing a lysophospholipid (not plasmalogens.) Lysophospholipases remove the remaining fatty acid. 34

35 Phospholipase A 2 catalyzes the hydrolysis of glycerophospholipids to form a free fatty acid + lysophospholipid. Phospholipases A 1, A 2, B, C, and D attack the bonds indicated in Figure. Phospholipase A 2 is found in pancreatic fluid and snake venom as well as in many types of cells. Phospholipase C is one of the major toxins secreted by bacteria. Phospholipase D is known to be involved in mammalian signal transduction. Lysolecithin (lysophosphatidylcholine) may be formed by an alternative route that involves lecithin:cholesterol acyltransferase (LCAT). 35

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37 Structural lipids present in the membranes of most eukaryotic cells. The characteristic structure is the steroid nucleus, consisting of four fused rings, three with six carbons and one with five. 37

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39 Cholesterol - The major sterol in animal tissues - Amphipathic compound - Cholesterol is precursor of Steroid hormones, Bile salts & Vitamin D - Cholesterol deposits in coronary artery wall led to Atherosclerosis & MI - Synthesis in cytosol from AcCoA - Statins are cholestrol-lower agents 39

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41 Vitamin D 41

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43 Ubiquinone: Dolichol: Free Radicals: 43

44 LIPID PEROXIDATION IS A SOURCE OF FREE RADICALS 44

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48 Lipoproteins For lipid transfer in tissues They are amphipatic According to density: 1- Chylomicron 2- VLDL 3- LDL 4- HDL - IDL & LPL - Lipoproteins & Atherosclerosis (Role of Estrogen) 48

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51 Cell Membrane 51

52 Cell Membrane Bilayer amphipathic structure consist of: Lipid + Proteins + - Cholestrol Proteins are peripheral & Integral (transmembrane)- Membrane proteins have roles as: receptor, antigen, - transporter for cell/cell interaction & selective transporter 52