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Medical Biochemistry (2) Level 2 Part V (Lipids)
Taif University College of Medicine Preparatory Year Students Medical Biochemistry (2) Level 2 Part V (Lipids)
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Lipids
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Lectures outlines Definition and importance of lipids
Classification of lipids Fatty acids structure and properties Important reactions of FA Glycerides Non-glyceride lipids Membranes Lipids
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What are lipids?
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Definition A collection of organic molecules of varying chemical composition. They are grouped together on the basis of their solubility in nonpolar solvents (ether, chloroform, benzene, acetone) but insoluble in water. Lipids include fats, oils, waxes and related compounds. They are widely distributed in nature both in plants and in animals.
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The great structural diversity among lipids
The defining parameter for lipids is solubility rather than structure.
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What are the Biological Functions of Lipids?
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The biological functions of lipids
Energy source (Fatty acids) Energy storage (triacylglycerols) Structural components of cell membrane (phospholipids, sphingoglycolipids, and cholesterol) Hormones (steroid hormones) Emulsifiers (Bile salts) Protection and insulation (biological waxes) Source of Fat-soluble Vitamins Vitamins absorption
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What are the Classes of Lipids?
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Lipids Classification
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What is the general structure of fatty acids?
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Nonpolar Hydrophobic Tail
Fatty Acids Usual fatty acids are unbranched Aliphatic carboxylic acids Nonpolar Hydrophobic Tail polar Hydrophilic Head Saturated Unsaturated R without double bonds have carbon-carbon double bonds
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Fatty Acids Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from triglycerides or phospholipids. When they are not attached to other molecules, they are known as "free" fatty acids. Fatty acids are important sources of fuel because they yield large quantities of ATP. Many cell types can use either glucose or fatty acids for this purpose. In particular, heart and skeletal muscle prefer fatty acids.
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Length of free fatty acid chains
Fatty acid chains differ by length, often categorized as short to very long. aliphatic tails < 6 carbons Short-chain fatty acids (SCFA) aliphatic tails carbons Medium-chain fatty acids (MCFA) aliphatic tails carbons Long-chain fatty acids (LCFA) aliphatic tails > 23 carbons Very long chain fatty acids (VLCFA)
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Fatty Acids Common fatty acids
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Fatty Acids Fatty acids
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Unsaturated fatty acids
Common Fatty Acids
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Dealt () Omega () 18:2 9,12 18:2 6,9 Linoleic acid 18:2
Fatty Acids Dealt () Omega () Numbering -COOH -CH3 -COOH -CH3 9 12 9 6 18:2 9,12 18:2 6,9 Linoleic acid 18:2
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Omega-3 & Omega-6 fatty acids
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Systematic nomenclature
Stearic acid are non-systematic historical names, which are the most frequent naming system used in literature Trivial nomenclature (or common names) octadecanoic acid derive from the standard IUPAC Rules for the Nomenclature of Organic Chemistry Systematic nomenclature (IUPAC names) 18:2 9,12 the location of the double, counting from the carboxylic acid end. Δx nomenclature (or delta-x) 18:2 6,9 the location of the double, counting from the terminal methyl carbon ωx nomenclature (or omega –x) Lipid numbers take the form C:D where: C = the number of carbon atoms and D = the number of double bonds in the fatty acid
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Summary of the ways for designating fatty acids
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Lecture notes (Dr Gaber Shehab)
Essential fatty acids Fatty acids that are required by the human body but cannot be made in sufficient quantity from other substrates, and therefore must be obtained from food. There are two essential fatty acids: linoleic acid and linolenic acid. These two acids: (1) are needed for proper membrane structure and (2) serve as starting materials for the production of several nutritionally important longer-chain omega-6 and omega-3 acids Linoleic acid (18:2) is the primary member of the omega-6 acid family, and linolenic acid (18:3) is the primary member of the omega-3 acid family. Biochemistry Department
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Questions What are the differences between saturated and unsaturated fatty acids? Write the chemical structure, the IUPAC name, the delta and the omega number of the following fatty acids: Palmitic Stearic Palmitoleic Oleic Linoleic Linolenic
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IUPA name and structure of common fatty acids
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Important reactions of FA
Esterification Hydrolysis of esters Hydrogenation Effect of radiation
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Esterification
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Esterification Fatty acids + Alcohol H +/ Heat Ester + Water
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Hydrolysis of esters Acid hydrolysis Base hydrolysis (Saponification)
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Acid Hydrolysis Ester H +/ Heat Acid + Alcohol
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Base Hydrolysis Ester Saponification OH - Salt of the acid + Alcohol
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Hydrogenation
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Hydrogenation Oleic acid Stearic acid
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Lecture notes (Dr Gaber Shehab)
Effect of radiation Splitting the Bay bond- Free rotation – Reforming the bond Changing the configuration of the double bond Biochemistry Department
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Lecture notes (Dr Gaber Shehab)
Effect of radiation Splitting the C-C bond- Biochemistry Department
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Classification Scheme for Fatty acids
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Glycerides
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Lipids Classification
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Neutral- glycerides Phospho- Glycerides
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Neutral -glycerides
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Esters of Fatty acids with Glycerol
Glycerides Neutral glycerides Esters of Fatty acids with Glycerol
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Esterification HO 3 H2O Ester Bond Triglyceride
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Structure of the simple triacylglycerol
The simple triacylglycerol produced from the triple esterification reaction between glycerol and three molecules of stearic acid (18:0 acid). Three molecules of water are a by-product of this reaction.
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Structure of a mixed triacylglycerol
Three different fatty acid residues are present
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Triglycerides Monoacid Mixed Di-acid Tri-acid Triglycerides Tristearin
Palmito, Oleo, Stearin Stearo, Stearo, Palmitin
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Question Draw the structural formula of the triacylglycerol produced from the reaction between glycerol and three molecules of oleic acid?
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Hydrolysis of Triglycerides
Glycerol Enzymatic or Acid Hydrolysis Lipase Alkaline Hydrolysis Glycerol Saponification
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