Classes of Lipids fatty acids Fat soluble vitamins eicosanoids * steroids triacylglycerols glycolipids *waxes phospholipids * fatty acids absent

Functions Energy source Hydrophobic barriers Functional storage compounds (triacyl glycerols) Hydrophobic barriers membrane constituents (phospholipids & glycoplipids) Functional protective coverings (waxes) regulatory properties e.g. coenzymes hormones (steroids, prostaglandins,vitamins) signalling e.g. odours

1.FATTY ACIDS General structure Ionised at pH7 amphipathic O O hydrophilic carboxyl group C hydrophobic hydrocarbon chain

Aggregates of Fatty Acids Hydrophobic tail Surface film Hydrophilic head micelle water

SATURATED FATTY ACIDS Typical example:stearic acid Sat FA Highly flexible - free rotation around each C-c bond. Pack together tightly in near crystalline array along their length. VW contact with neighbouring mols. Diag Lehninger p242 Mp increase with molecular mass Typical example:stearic acid

MONOUNSATURATED FATTY ACIDS e.g. OLEIC ACID - 18:1 Unsat FA Unsat common - 1. Monounsat polyunsat - up to 6 double bonds per chain. Triple bonds rare.

POLYUNSATURATED ACIDS LINOLEIC ACID - 18:2 Both bonds are cis

Acid name Symbol Function Mp C 63.1 -0.5 69.6 13.4 Acid name Symbol Function Butyric 4:0 Occur Capric 10.0 in milk Palmitic * 16.0 Structural Palmitoleic 16.1(9) lipids and Stearic 18.0 triacylglycerols Oleic acid* 18.1(9) Linoleic* 18.2 essential fatty Linolenic 18.3 acids Arachidonic 20:4(5,8,11,14) Precursor of prostaglandins Lignoceric 24:0 Components of Nervonic 24.1(15) cerebrosides * predominant fatty acid residues in cells

Link between metabolism of carbohydrates, fats and amino acids Sugars glycolysis TCA Cycle AcetylCoA Pyruvate AcetylCoA Palmitic acid 16.0 Elongation Desaturation Amino acids mitochondrion Various Fatty Acids

Synthesis of Fatty Acids: 2 carbon additions Palmitate 16.0 elongation Stearate 18.0 desaturation Oleate 18.1(9) Linoleate 18.2 (9,12) Arachidonate 20.4 (5.8.11.14) Linolenate 18.3 (9,12,15) Other poly unsaturated FA EICONASOIDS

General formula CH3 (CH2) nCOO Amphipathic Structure Fatty acids: Summary General formula CH3 (CH2) nCOO Amphipathic Structure C16 -20 (biological) unsaturated / mono or polysaturated cis configuration branching simple Rarely free Alkyl chain+ terminal carboxylic group Usually even no C atoms. 16.18. or 20 common. Long chains in nervous system e.g. C22 + 6 double bonds in nervonic acid. . Unsat common - up to 6 double bonds per chain. Triple bonds rare. Numerical system indicates structure (p364) A few have alpha-OH group. More oxidised forms only produces duringenergy production or specific physiol cases e.g. prostaglandins. Branching simple, limited to methyl groups. E.g. isovaleric acid in echo-locating structures of mammals. Free FA have free -COOH and circulate in the blood bound to serum albumin. But Most occur as esters of glycerol or amides. Lacking the carboxylate group they are less soluble then FA = stored for future use.

TRIACYLGLYCEROL

Adipocyte cytoplasm triacylglycerol nucleus 10μm Energy store Lipases in adipocytes and germ seeds break down TAG, releasing FA for export and fuel. Advantage as store cf- polysac. 1.C more reduced Oxidation gives twice as much energy per g as carbs. 2.Hydrophobic so organism does not need to carry weight of water of hydration assoc with stored polysacs. 3.Mols cluster - adopt position of minimal contact with aq surroundings - cannotparticipate in formation of membranes Human - glycogen store = 6 h, although quick source of energy. Fat tissue (adipose under skin, in abdominal cavity and mammary glands) Obese = 15 - 20kg TAG in adipocytes. - can supply energy need for months. nucleus

Sperm Whale Spermaceti organ