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Lipid Chemistry

Lipid Chemistry. - Lipids are organic compounds formed mainly from alcohol and fatty acids combined together by ester linkage. Lipids are insoluble in water, but soluble in fat or organic solvents (ether, chloroform, benzene, acetone, etc.).

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Lipid Chemistry

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  1. Lipid Chemistry -Lipids are organic compounds formed mainly from alcohol and fatty acids combined together by ester linkage. Lipids are insoluble in water, but soluble in fat or organic solvents (ether, chloroform, benzene, acetone, etc.). Lipids include fats, oils, waxes and related compounds. They are widely distributed in nature both in plants and in animals.

  2. Biological Importance of Lipids: Lipids are important dietary constituents, because of the following reasons: • They are more palatable and storable to unlimited amount compared to carbohydrates. • They have a high-energy value (25% of body needs) and they provide more energy per gramthan carbohydrates and proteins but carbohydrates are the preferable source of energy..

  3. Supply the essential fatty acids that cannot be synthesized by the body. • Supply the body with fat-soluble vitamins (A, D, E and K). • They are important constituents of the nervous system “Neurolemma”. • Tissue fat “constant fat” is an essential constituent of cell membrane and nervous system. It is mainly phospholipids in nature that are not affected by starvation. • Stored lipids “depot fat” are stored mainly in adipocytes. It is mainly triglycerides in nature and acts as:

  4. -A store of energy. • -A pad for the internal organs to protect them from outside shocks. • -A subcutaneous thermal insulator against loss of body heat. • Lipoproteins, which are complex of lipids and proteins, are important cellular constituents that present both in the cellular and subcellular membranes. • Cholesterol enters in membrane structure and is used for synthesis of adrenal cortical hormones, vitamin D3 and bile acids. • Understanding biochemistry of lipids provide bases for dealing with diseases such as obesity, atherosclerosis, lipid-storage diseases, essential fatty acid deficiency, respiratory distress syndrome,.. etc.

  5. Classification of Lipids Lipids are classified into: I- Simple lipids:They are esters of fatty acids with fatty alcohol. They are called neutral lipids due to absence of ionizable groups (i.e., uncharged). They are classified according to the alcohol present into: • Neutral fats:Esters of fatty acids with glycerol (triacylglycerols, or triglycerides). • Waxes: Esters of fatty acids with long-chain alcohols other than glycerol those are mostly monohydric. Cholesterol esters with any fatty acid are waxes. Esters of vitamin A and vitamin D with fatty acid, e.g., palmitic or stearic acid are waxes, too.

  6. II- Compound or conjugated lipids: • They are esters of fatty acids and alcohols in additions to other groups They include the following types: • Phospholipids (phosphatides):Compound lipids containing fatty acids, alcohol, phosphoric acid and often a nitrogenous base. They are further classified according to the alcohol moiety into: (a)-glycerophospholipids where the alcohol is glycerol. (b)-sphingophospholipids where the alcohol is sphingosine. • Glycolipids:Compound lipids containing fatty acids, carbohydrate and sphingosine, but not phosphoric acid nor glycerol. • Lipoproteins:Compound lipids composed of a lipid part associating by secondary bonds with proteins as plasma and membranous lipoproteins.

  7. Other compound lipids:include: • -Sulfolipids: containing sulfur • -Aminolipids: containing amino acids • III- Derived Lipids: • They are products of hydrolysis of simple and compound lipids and/or their derivatives that still possess the general characteristics of lipids. They include: • Fatty acids, monoglycerides and aldehydes. • Alcohols including glycerol. • Sterols, steroids and hormonal derivatives of vitamin D. • Eicosanoids (prostaglandins, leukotrienes and thromboxanes). • Ketone bodies.

  8. IV- Lipid-associatingsubstances: They include fat-soluble vitamins (E and K), carotenoids, squalene and hydrocarbons. • Alcohols • Alcohols associated with lipids include: glycerol, cholesterol and higher alcohols (e.g. cetyl alcohol, mericyl alcohol, dolicols……….etc.). • Glycerol • It is a trihydric alcohol (i.e., containing three OH groups) and has the popular name glycerin. It is synthesized in the body from glucose. It has the following properties: • Colorless viscous oily liquid with sweet taste. • Soluble in water and alcohols and insoluble in non polar fat solvents. • On heating with sulfuric acid or KHSO4 (dehydration) it gives acrolein (acryl aldehyde) that has a bad odour. This reaction is used for detection of free glycerol or any compoundcontaining glycerol.

  9. It combines with three molecules of nitric acid to form trinitroglycerin (TNT) that is used as explosive and vasodilator. • On esterification with fatty acids it gives: Monoglyceride or monoacyl-glycerol: one fatty acid + glycerol. Diglyceride or diacyl-glycerol: two fatty acids + glycerol. Triglyceride or triacyl-glycerol: three fatty acids + glycerol.

  10. It has a nutritive value by conversion into glucose and enters in structure of phospholipids. • Uses of Glycerol: • Glycerol enters in pharmaceutical and cosmetic preparations (hygroscopic). • Nitroglycerin (glyceryl trinitrate) is used as vasodilator especially for the coronary arteries, thus it is used in treatment of angina pectoris. Also, enters in explosives manufacturing. • Glycerol is used in treatment of glaucoma (increased intraocular pressure) due to its ability to dehydrate the tissue from its water content.

  11. Sphingosine • It is the alcohol present in sphingolipids. • It is synthesized in the body from serine and palmitic acid. It is not positive with acrolein test.

  12. Fatty Acids Definition: • Fatty acids are aliphatic mono-carboxylic acids that are mostly obtained from the hydrolysis of natural fats and oils. • They have the general formula R-(CH2) n-COOH and mostly have straight chain (a few exceptions have branched and heterocyclic chains). In this formula "n" is mostly an even number of carbon atoms (2-34) with a few exceptions that have an odd number or even zero in acetic acid.

  13. Fatty acids can be classified as :follows • I) Saturated they contain no double bonds with 2-24 or more carbons. They are solid at room temperature except if they are short chained. They may be even or odd numbered. They have the following molecular formula, CnH2n+1COOH. Examples are butyric, palmitic and stearic acids.

  14. II) Unsaturated) • they contain one (monounsaturated, CnH2n-1COOH) or more double bonds (polyunsaturated, CnH2n-more than 1COOH). • Some fatty acids may contain hydroxyl or ketogroups, few cyclic fatty acids are known.

  15. A-Short-chain fatty acids: They have 2-10 carbons. They are soluble in water and are present in milk in high amount. They are further classified into: • i) Volatile short-chain fatty acids: They are liquid in nature and contain 2-6 carbon atoms, water-soluble and volatile at room temperature, e.g., acetic, propionic, butyric, valeric and caproic acids. • 2C Acetic acid CH3-COOH • 3C Propionic acid CH3-CH2-COOH • 4C Butyric acid CH3-(CH2)2-COOH (in butter fat) • 5C Valeric acid CH3-(CH2)3-COOH • 6C Caproic acid CH3-(CH2)4-COOH

  16. ii) Non-volatile short-chain fatty acids:They are solid at room temperature and contain 7-10 carbon atoms. They are water-insoluble and non-volatile at room temperature. Examples of non-volatile short-chain fatty acids include caprylic and capric acids. • 8C Caprylic acid CH3-(CH2)6-COOH • 10C Capric acid CH3-(CH2)8-COOH

  17. B- Long-chain fatty acids:They contain more than 10 carbon atoms. They occur in hydrogenated oils, animal fats, butter and coconut and palm oils and other plant oils. They are non-volatile, water-insoluble and solid (if saturated) or liquid (if unsaturated) at room temperature. Examples of saturated long-chain fatty acids include lauric, myristic, palmitic, stearic, arachidic, behenic and lignoceric acids. • 12C Lauric acid CH3-(CH2)10-COOH • 14C Myrestic acid CH3-(CH2)12-COOH • 16C Palmitic acid CH3-(CH2)14-COOH • 18C Stearic acid CH3-(CH2)16-COOH • 20C Arachidic acid CH3-(CH2)18-COOH • 22C Behenic acid CH3-(CH2)20-COOH • 24C Lignoceric acid CH3-(CH2)22-COOH

  18. Unsaturated fatty acidsII- • - They are called unsaturated because of the presence of double bonds. • - The presence of double bonds affects their physical properties, e.g., decreasing the melting temperature, therefore, all unsaturated fatty acids are liquids at room temperature.

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