Lipids 1 References Organic and biochemistry for today

Lipids 1

References: *Organic and biochemistry for today by Spencer. *Biochemistry by Armstrong. *Modern biochemistry by Werner. 2

* Definition and classification. * Fatty acids. * Triglycerides neutral fats and oils. * Triglycerides reactions. * Waxes. *Phospholipids. *Sphingolipids. *Biological membrane. *Isoprenoids. *Steroids. *Prostaglandines.

Lipids Lipid is made up of substances with widely different compositions and structures , it defined in term of physical property (solubility) , insoluble in water but soluble in non polar solvents. Lipids are the waxy, greasy or oily compounds found in plants and animals. lipid repel water , a useful characteristic of protective wax coatings found in some plants. 4

Fats and oils are energy rich , it can storage in plants and animals and structural component like cell membrans. Lipid can be grouped into two main classes: *Saponifiable lipids. *Non. Saponifiable lipids. Saponification: the process in which esters are hydrolyzed under basic conditions (Na. OH, KOH). 5

Saponifiable lipids like: * Triglycerides. * Waxes. * Phospholipids. * Sphingolipids. Nonsaponifiable lipids: are not esters and can not hydrolyzed like: *Isoprenoids. *Steroids. *Prostaglandines. 6

Saponifiable lipids can be classefied also into: *Simple lipids (fatty acid+ alcohol) and includes waxes and triglyceride. *Complex lipids (fatty acid + alcohol + other compounds) and includes phosphoglycerides and sphingolipids. Fatty acids : The fundamental building blocks of many lipids and are long chain carboxylic acid. The long nonpolar tail of F. A. that are responsible for most of the fatty or oily characteristics of fats. 7

Carboxylic group, polar head of F. A is very hydrophilic under conditions of physiological p. H and it exists as the carboxylate anion COO¯. A 16 C fatty acid: CH 3(CH 2)14 COO Non polar polar A 16 C fatty acid with one cis double bond between C atoms 9 10 may be represented as 16: 1 cis D 9. In aqueous solution the ion of F. As associated with one another and form spherical clusters called Micelles: in which the non polar chain extend toward the interior of the structure a way from water and the polar carboxylate groups face outward in contact with the water (some time contain hundreds or thousands of F. As). 8

F. As held together by weak dispersion forces. Micelle is important in transport of insoluble lipids in the blood. CH 3—CH 2—CH 2—COOH ↓ Non polar hydrophobic Polar hydrophilic head tail water insoluble (water soluble) 9

Micelle 10

The F. As found in natural lipids have several characteristics: 1. They are usually straight chain carboxylic acids (no branching). 2. The size of F. As range 10 20 carbons. 3. F. As usually have even number of carbon atoms including carbonyl carbon. 4. F. As can be saturated (no double bonds)or unsaturated contain one or more double bonds and found in cis configuration. 11

This configuration creates a long characteristic bend or kink in F. As chains that is not found in saturated F. As. These kinks prevent unsaturated F. As chains from packing together as do the chains of saturated F. As. As a result, the intermolecular forces are weaker and unsaturated F. As have lower melting points and are usually liquids at room temperature. 12

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The presence of double bond and the length of F. A chain in membrane lipids partly explain the fluidity of biological membranes. Human body can synthesis all F. As except two (linoleic acid , linolenic acid) which are polyunsaturated F. As that contain 18 C atom, it must be obtained from the diet they are called Essential F. As: A fatty acid needed by the body but not synthesized within the body , it distributed in plants and fish oils. In body , both acids used to produce hormone like substances that regulate a wide range of functions and characteristic including blood pruessre, blood clotting , blood lipid level , immune response to injury and infections. 15

Linolenic acid called omega 3 F. A which mean the endmost double bond is three carbons from the methyl end chain. linolenic acid (fish oil) CH 3─CH 2─(CH=CH─CH 2)3─(CH 2)6─COOH 3 Linoleic acid an omega 6 F. A the endmost double bond is located six carbons from the methyl end of the chain. 16

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and the both acids can be converted to other omega 3 and 6 F. As. linoleic acid (vegetable oil ) CH 3─(CH 2)4─CH=CH─CH 2─CH=CH─(CH 2)7─COOH Some fatty acids and their common names: 14: 0 myristic acid; 16: 0 palmitic acid; 18: 0 stearic acid; 18: 1 cis. D 9 oleic acid 18: 2 cis. D 9, 12 linoleic acid 18: 3 cis. D 9, 12, 15 a-linonenic acid 20: 4 cis. D 5, 8, 11, 14 arachidonic acid 18

Animal fats and vegetable oils are the most widely occurring lipids. Fats and oils are both esters, ester consist of an alcohol portion and an acid portion. 19

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Natural T. g (fats and oils) are usually mixture of different T. g molecules, for example butter fat contains 14 different F. As components. Fat: A triglyceride that is a solid at room temperature and come from animals it contain long chain saturated F. As(higher melting points). Oil: A triglyceride that is a liquid at room temperature and come from plant or fish. Vegetable oil such as corn, sunflower oils consists of unsaturated F. A(lower melting point). 21

Olive oil Contains a high percentage of oleic acid, which is a monounsaturated fatty acid with one cis double bond. 22

Triglyceride reactions: 1. Hydrolysis: most important reaction in fats and oils it’s the reveres to ester formation. Enzymes (lipases) of the digestive system also catalyze the hydrolysis to supply energy. +3 +3 23

2. Saponification: (soap making) soap: A salt of a F. A often used as a cleaning agent. Sodium salts →hard salt → cake soap used in home. Potassium salts →soft salt →sharing creams and liquid soap. “soap” 24

+ 3 Na. OH +3 “soap” 25

3. Hydrogenation: double bond can be reduced to single bond by treatment with hydrogen H 2 in the presence of catalyst. It is commercial reaction of fats and oils and therefore increase the melting point , it is most often used in the production of semisolid cooking shortening (margarines) from liquid vegetable oils. 26

Hydrogenation: Ni + 3 H 2 glyceryl tripalmitoleate (tripalmitolean) glyceryl tripalmitate (tripalmitin) 27

Some cis F. A in hydrogenation isomerizes to trans F. A (Bad F. A). 28

Waxes : An ester of a long chain F. A and long chain alcohol (13 32 carbon). Waxes insoluble in water and not as easily hydrolyzed as fat and oil , they occur naturally in nature as protective coating on feathers, skin , fruits, leaves. 29

Phosphoglycerides (Phospholipids) : A complex lipid contains glycerol, F. As, phosphoric acid , and an amino alcohol component. Fatty acid Glycerol Fatty acid PO 4 Amino alcohol Phosphoglycerides are the major component of cell membranes. 30

Phosphoglycerides have different amino alcohol groups like: CH 3 │+ + HO−CH 2−N−CH 3 HO−CH 2−NH 3 │ choline CH 3 ethanolamine + NH 3 │ Amino alcohols HO−CH 2−CH−COO− serine 31

Lecithin and cephalin are glycerophospholipids Abundant in brain and nerve tissues. Found in egg yolk, wheat germ, and yeast. 32

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Sphingolipids: A complex lipid contain sphingosine compound (along chain unsaturated amino alcohol , an 18 carbon alcohol ) instead of glycerol, F. As, phosphoric acid , and an amino alcohol component. they found in cell membrane like: sphingomyelin , glycolipid. fatty acid sphingosine PO 4 Amino alcohol CH 3−(CH 2)12 −CH=CH−CH−OH │ sphingosine CH−NH 2 │ CH 2−OH 34

Sphingomyelin: a sphingolipid found in brain and nerve tissue and in protective myelin sheath that surrounds nerves. It is acomplex lipid contain a siphingosin , F. A, cholin. There is an amide bond between a fatty acid and sphingosine. 35

Glycolipids: A complex lipid contain a siphingosin , F. A , a carbohydrate (glucose or galactose)and often called cerebrosides because of their abundance in brain tissues. 36

Biological membrane : Membranes performed two vital functions in living organisms : The external cell membrane: acts as a selective barrier between the living cell and its environment. The internal membrane: surround some organelles , creating cellular compartments that have separate organization and functions. Lipid bilayer: A structure found in membranes, consisting of two sheets of lipid molecules arranged so that the hydrophobic portions are facing each other. 37

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Cell membranes contain lipid , protein and carbohydrates. Phosphoglycerides such as (lecithin, cephalin) and sphingomyelin, cholesterol are lipids found in membranes. The lipids are organized in a bilayer in which the hydrophobic chains extend toward the inside of bilayer and the hydrophilic groups(the phosphate groups and other polar groups ) are oriented toward the outside, where they come in contact with water, like the micelle. Membrane lipids usually contain unsaturated F. As chains that fit into bilayer more loosely than do saturated F. As. This increases the flexibility or fluidity of the membrane. 39

Fluid Mosaic Model of Cell Membranes 40

Isoprenoids : Are a vast array of biomlecules that contain repeating five carbon structural units known as isoprene (methylbutadiene) units. The isoprenoids consist of terpenes and steroids. Terpenes : They are linear or cyclic compounds formed by condensation of two or more isoprene units and are found largely in the essential oils of plants (have been used in perfumes and medicine), like vitamin A, K, E , carotenes , sequaline. 41

Terpenes 42

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Steroids: They are completely different from the lipids, and defined: are compound contain four rings fused in a particular pattern (three six membered rings and a single five membered ring fused together) , like: 44

1. Cholesterol: most abundant lipid in human body (cellular membranes , myelin sheath, brain, and nerve tissues) and has a rigid ring system and a short branched hydrocarbon tail. Cholesterol is largely hydrophobic. But it has one polar group, a hydroxyl, making it amphipathic. Cholesterol inserts into bilayer membranes with its hydroxyl group oriented toward the aqueous phase & its hydrophobic ring system adjacent to fatty acid chains of phospholipids. The OH group of cholesterol forms hydrogen bonds with polar phospholipid head groups. 45

Cholesterol is a precursor for other important steroids including : Bile salts Hormones Vitamin D 46

Usually; saturated fat in diet cause high blood cholesterol level and these consider risk factor of coronary heart diseases. 47

2. Bile salt : is a yellowish brown or green liver secretion that is stored and concentrated in the gallbladder. It is important in lipid digestion. 48

Polar region Non polar region 49

3. Steroid Hormons: A chemical messenger secreted by specific glands and carried by the blood to a target tissue, where it triggers a particular response. 50

Adrenocorticoid Hs. : Adernal glands are small mounds of tissue located at the top of each kidney. The outer layer of the gland , the adrenal cortex , produse a number of potent steroid Hs. , the adrenocorticoids are classified in to: ↙ ↘ Mineralocrticoids Glucocorticoids regulate concentrations enhance carbohydrates of Na⁺ in body fluids metabolism ( aldosterone ) (cortisol) 51

aldosterone, which regulates electrolytes and water balance by the kidneys. cortisone, a glucocorticoid, which increases blood glucose level and stimulates the synthesis of glycogen in the liver. 52

Sex hormons: the tests and ovaries produce steroids that functions as sex Hs, which are responsable of secondary sex characteristic appearnase. Tests in male produce Ovaries in female produce sperm and male sex H. estrogen and progesterone. testesrone (androgen). 53

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Prostaglandines (PGs): This group of compounds was given its name because the first prostaglandins were identified from the secretion of the male prostate gland , there about 20 prostaglandins in a variety of tissues within both male and female. Prostaglandin: A substance derived from unsaturated F. A with hormone like effects on a number of body tissues and is a cyclic compound synthesized in the body from the 20 carbon unsaturated F. A arachidonic acid , like prostaglandin E 2 (PGE 2). 55

Clinically, PGs have many functions as stimulate blood clotting , involved in every phase of reproductive process. 56

Prostaglandins are: • Produced by injured tissues. • Involved in pain, fever, and inflammation. • Not produced when anti inflammatory drugs such as aspirin inhibit their synthesis. 57