Lipids 1 24-25 2024/2025 PDF

Department of Biochemistry Faculty of Medicine – Umm Alqura University Basics of Biochemistry First Year – MBBS & Dentistry program 1446 H- 2024/2025 g Biochemical Aspects of Lipids I Fatty Acids  O ut lin es St r uct ur e, f o r m ula , n...

Department of Biochemistry Faculty of Medicine – Umm Alqura University Basics of Biochemistry First Year – MBBS & Dentistry program 1446 H- 2024/2025 g Biochemical Aspects of Lipids I Fatty Acids  O ut lin es St r uct ur e, f o r m ula , n o m en cla t ur e o f Fa t t y a cid s (FA ). FA cla ssif ica t io n (sa t ur a t io n – essen t ia lit y cla ssif ica t io n ). M ed ica l a n d n ut r it io n a l a p p lica t io n s: O liv e o ils – O m eg a FA – Pr o st a g la n d in s – eico sa n o id s. O il h y d r o g en a t io n lipids lipids are organic compounds formed by esters of fatty acids with alcohols 1 1 2 2 3 3 alcohols fatty acids Fatty Acids ▪ They are carboxylic acids with hydrocarbon chains ranging from 4 to 36 carbon atoms. ▪ The most commonly occurring fatty acids have even numbers of carbon atoms of 12 to 24 carbons ▪ Insoluble in water. ▪ Saturated or unsaturated.  Fatty acids Fatty Acid Formulas The formulas for fatty acids are written as condensed and line-bond formulas. For example fatty acid with 8 carbon atoms can be written as: General nomenclature The carbon atoms of a fatty acid are numbered (or lettered with Greek lettering system, from the carboxyl group (carbon no.1), carbon atoms next to it (Nos. 2, 3, and 4) are named (α, β, γ). Or from the carbon farthest removed from the carboxyl group (the terminal methyl carbon is known as the ω or n-carbon. (n or omega numbering system) CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH 10 9 8 7 6 5 4 3 2 1 1 2 3 4 5 6 7 8 9 10 ω δ γ β α Systematic names ▪ Saturated fatty acids end in -anoic, eg, octanoic acid. ▪ Unsaturated acids with double bonds end in-enoic, eg, octadecenoic acid (oleic acid). ▪ The position of a double bond is represented by the symbol ∆ followed by a superscript number eg, ∆9 indicates a double bond between carbons 9 and 10 of the fatty acid. Fatty acids are divided into: 1. Saturated 2. Unsaturated a. Monounsaturated (monoenoic) acids, containing one double bond. b. Polyunsaturated (polyenoic) acids, containing two or more double bonds. c. Eicosanoids: These compounds are derived from eicosa- (20- carbon) polyenoic fatty acids, e.g. leukotrienes (LTs), prostaglandins and thromboxanes (TXs). 1. Saturated F.As. Saturated fatty acids have single C–C bonds Saturated F.As. Molecules that fit closely together in a regular pattern. Strong attractions between fatty acid chains. High melting points that makes them solids at room temperature. 2. Unsaturated F.As. Most Naturally Occurring Unsaturated have cis C=C bonds Unsaturated F.As. Unsaturated fatty acids typically contain cis double bonds. Unsaturated F.As. Unsaturated fatty acids: Have nonlinear chains that do not allow molecules to pack closely (because of the cis-double bonds). Have low melting points. Are liquids at room temperature. Olive Oil Olive oil contains a high percentage of oleic acid. Oleic acid is a monounsaturated fatty acid with one cis double bond. Omega-6 and Omega-3 F.As. The first double bond: At carbon 6 (omega-6) (e.g. vegetable oils) At carbon 3 (omega-3) (e.g. fish oils) Essential fatty acids Essential fatty acids that can not be synthesized in the body and must be taken in adequate amounts in the diet. Mammals cannot synthesize the two main types of polyunsaturated fatty acids: the linoleic (omega-6) and linolenic (omega-3). Essential fatty acid deficiency is characterized by nutrition deficiency disease, e.g dermatitis and poor wound healing Most prostaglandins are synthesized from arachidonic acid (a linoleic acid derivative). Lack of these prostaglandins causes some aspects of the essential fatty acid deficiency syndrome. Essential fatty acids A small daily intake of linolenic acid is recommended (this may be especially important when the nervous system is developing). Docosahexaenoic acid: A conditionally essential FA (22:6 3,6,9,12,15,18) is needed for maximum development of the visual and central nervous systems during the neonatal period (it is present in large amounts in the retina and parts of the brain; it enhances the visual response and the function of certain domains in neural membranes). 3. Eicosanoids: Eicosanoids: These compounds are derived from eicosa- (20-carbon) polyenoic fatty acids (eg, arachidonic acid) eg, prostaglandins, leukotrienes (LTs) and thromboxanes (TXs). Prostaglandins ▪ Are synthesized in the body from an eicosanoic polyunsaturated fatty acid (arachidonic acid) ▪ Have important physiologic and pharmacologic activities. ▪ Have 20 carbon atoms in their fatty acid chains. ▪ An OH on carbon 11 and 15. ▪ A trans double bond at carbon 13. ▪ Different substituent groups attached to the rings give series of prostaglandins eg, the “E” type of prostaglandin (as in PGE1) has a keto group in position 9, whereas the “F” type has a hydroxyl group in this position. Prostaglandins  Prostaglandins in the Body Prostaglandins are: Produced by injured tissues. Involved in pain, fever, and inflammation. Not produced when anti-inflammatory drugs such as aspirin inhibit their synthesis. Thromboxanes & Leukotriens: When a cell responds to a stimulus, bioactive mediators (prostaglandins, thromboxanes, leukotrienes, and others) often are formed from the lipids contained in its membranes. Thromboxanes regulate blood coagulation. Leukotrienes play a role in allergic and inflammation responses. They were isolated from leukocytes (white blood cells). Hydrogenation (hardening) of Oils Hydrogenation: Adds hydrogen to double bonds in oils to form single bonds. Produces solid shortening, margarine, and other products.