Part II_B_Lipids - Part II Basic molecules of biochemistry...

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Part II. Basic molecules of biochemistry Lipids Structural classes 1
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2 Lipids – diverse class of molecules rich in carbon and hydrogen , but contain relatively few oxygen atoms ( lipo -, fat), often water-insoluble (common, defining feature) Two major functions, energy storage and membrane formation Also, signaling molecules ( e.g. , eicosanoids, steroid hormones), connective tissue formation, and vitamin high solubility in nonpolar organic solvents either hydrophobic (nonpolar), or amphipathic
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Part II. Basic molecules of biochemistry Lipids Fatty acids 3
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4 fatty acids general formula: R-COOH, where R represents a hydrocarbon chain differ in length of hydrocarbon tails, number of C-C double bonds , position of double bonds, and number of branches (generally 4 to 36 C atoms long, most common have unbranched chains 12 to 20 C long)
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5 structure and nomenclature of fatty acids laurate (or dodecanoate) most fatty acids have p K a around 4.5 to 5.0 (ionized at physiological pH) form of detergent (long hydrophobic tail and polar head group) concentration of free fatty acid in cells quite low, most are components of more complex lipids Shorthand notation : number of carbon atoms, number of C-C double bonds, and positions e.g ., palmitate, (hexadecanoate) 16:0 16 C atoms no double bonds oleate, cis - 9 -octadecenoate 18:1 9 18 C atoms 1 double bond double bond at position C9
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saturated and unsaturated fatty acids ( cis - 9 -octadecenoate) (all- cis - 9,12,15 -octadecatrienoate) 6 all are C 18 fatty acids differ in position and degree of unsaturation Different physiochemical properties
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Part II. Basic molecules of biochemistry Lipids Multiple bonds and fatty acid chain flexibility 7
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8 A double bond ( 2 pairs of shared electrons ) consists of a σ bond and a π bond. A triple bond ( 3 pairs of shared electrons ) consists of a σ bond and two π bonds. multiple bonds
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9 Ethane is composed of two methyl groups bonded by the overlap of their sp 3 hybrid orbitals . There is free rotation along single bonds.
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10 Pure conformers cannot be isolated in most cases, because the molecules are constantly rotating through all the possible conformations. conformations of ethane
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11 The totally eclipsed conformation is higher in energy because it forces the two end methyl groups so close together that their electron clouds experience a strong repulsion. This kind of interference between two bulky groups is called steric strain or steric hindrance . steric strain Butane
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