5 DefinitionA 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.
6 The great structural diversity among lipids The defining parameter for lipids is solubility rather than structure.
8 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 VitaminsVitamins absorption
15 Fatty AcidsMost 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.
16 Length of free fatty acid chains Fatty acid chains differ by length, often categorized as short to very long.aliphatic tails < 6 carbonsShort-chain fatty acids (SCFA)aliphatic tails carbonsMedium-chain fatty acids (MCFA)aliphatic tails carbonsLong-chain fatty acids (LCFA)aliphatic tails > 23 carbonsVery long chain fatty acids (VLCFA)
22 Systematic nomenclature Stearic acidare non-systematic historical names, which are the most frequent naming system used in literatureTrivial nomenclature(or common names)octadecanoic acidderive from the standard IUPAC Rules for the Nomenclature of Organic ChemistrySystematic nomenclature(IUPAC names)18:2 9,12the location of the double, counting from the carboxylic acid end.Δx nomenclature(or delta-x)18:2 6,9the location of the double, counting from the terminal methyl carbonωx nomenclature(or omega –x)Lipid numbers take the form C:D where:C = the number of carbon atoms andD = the number of double bonds in the fatty acid
23 Summary of the ways for designating fatty acids
24 Lecture notes (Dr Gaber Shehab) Essential fatty acidsFatty 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 andlinolenic 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 acidsLinoleic 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
25 QuestionsWhat 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:PalmiticStearicPalmitoleicOleicLinoleicLinolenic
44 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.
45 Structure of a mixed triacylglycerol Three different fatty acid residues are present