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Lipids

Pablo Jabalera Bioquímica Español 28 fichas

Fichas del conjunto (28)

112:0 CH3(CH2)10COOHn-Dodecanoic acid, Lauric acid
214:0 CH3(CH2)12COOHn-Tetradecanoic acid Myristic acid
316:0 CH3(CH2)14COOHn-Hexadecanoic acid Palmitic acid
418:0 CH3(CH2)16COOHn-Octadecanoic acid Stearic acid
520:0 CH3(CH2)18COOHn-Eicosanoic acid Arachidic acid
618:1(Δ9)cis-9-Octadecenoic Oleic acid
718:2(Δ9,12)Linoleic acid
818:3(Δ9,12,15)α-Linolenic acid
920:4(Δ5,8,11,14)Arachidonic acid
10—Triacylglycerol
11—L-Glycerol 3 -phosphate
12—
13—An unusual membrane lipid found only in some archaea.
(diphytanyl tetraether lipid)
14—N-Acetylneuraminic acid (a sialic acid)
(Neu5Ac)
15—
16—
17—Cholesterol
18—
19—Testosterone
20—Cortisol
21—β-estradiol
22—7-Dehydrocholesterol + UV light (2 steps in skin)
->
Cholecalciferol (vitamin D3) + 1 step in the liver 1 step in the kidney
->
1α,25-Dihydroxyvitamin D3
(calcitriol)
23—Vitamin A1
(retinol)
oxidation of alcohol to aldehyde ->
11-cis-Retinal(visual pigment) + visible light
->
all-trans-Retinal (Neuronal signal to brain)
24Summary storage lipids■Lipids are water-insoluble cellular components, of diverse structure, that can be extracted from tissues by nonpolar solvents.
■ Almost all fatty acids, the hydrocarbon components of many lipids, have an even number of carbon atoms (usually 12 to 24); they are either saturated or unsaturated, with double bonds almost always in the cis configuration.
■ Triacylglycerols contain three fatty acid molecules esterified to the three hydroxyl groups of glycerol. Simple triacylglycerols contain only one type of fatty acid; mixed triacylglycerols, two or three types. Triacylglycerols are primarily storage fats; they are present in many foods.
■ Partial hydrogenation of vegetable oils in the food industry converts some cis double bonds to the trans configuration. Trans fatty acids in the diet are an important risk factor for coronary heart disease.
■ Waxes are esters of long-chain fatty acids and long-chain alcohols
25SUMMARY - Structural Lipids in Membranes■ The polar lipids, with polar heads and nonpolar tails, are major components of membranes. The most abundant are the glycerophospholipids, which contain fatty acids esterified to two of the hydroxyl groups of glycerol, and a second alcohol, the head group, esterified to the third hydroxyl of glycerol via a phosphodiester bond. Other polar lipids are the sterols.
■ Glycerophospholipids differ in the structure of their head group; common glycerophospholipids are phosphatidylethanolamine and phosphatidylcholine. The polar heads of the glycerophospholipids are charged at pH near 7.
■ Chloroplast membranes are rich in galactolipids, composed of a diacylglycerol with one or two
linked galactose residues, and sulfolipids, diacylglycerols with a linked sulfonated sugar residue and thus a negatively charged head group.
26SUMMARY - Structural Lipids in Membranes II■ Some archaea have unique membrane lipids, with long-chain alkyl groups ether-linked to glycerol at each end and with sugar residues and/or phosphate joined to the glycerol to provide a polar or
charged head group. These lipids are stable under the harsh conditions in which these archaea live.
■ The sphingolipids contain sphingosine, a long-chain aliphatic amino alcohol, but no glycerol. Sphingomyelin has, in addition to phosphoric acid and choline, two long hydrocarbon chains, one contributed by a fatty acid and the other by sphingosine. Three other classes of sphingolipids are
cerebrosides, globosides, and gangliosides, which contain sugar components.
■ Sterols have four fused rings and a hydroxyl group. Cholesterol, the major sterol in animals, is both a structural component of membranes and precursor to a wide variety of steroids.
27SUMMARY - Lipids as Signals, Cofactors, and Pigments■ Some types of lipids, although present in relatively small quantities, play critical roles as cofactors or signals.
■ Phosphatidylinositol bisphosphate is hydrolyzed to yield two intracellular messengers, diacylglycerol and inositol 1,4,5-trisphosphate. Phosphatidylinositol 3,4,5-trisphosphate is a nucleation point for supramolecular protein complexes involved in biological signaling.
■ Prostaglandins, thromboxanes, leukotrienes, and lipoxins, all of which are eicosanoids derived from arachidonate, are extremely potent hormones.
■ Steroid hormones, such as the sex hormones, are derived from sterols. They serve as powerful biological signals, altering gene expression in target cells.
28SUMMARY - Lipids as Signals, Cofactors, and Pigments II■ Vitamins D, A, E, and K are fat-soluble compounds made up of isoprene units. All play essential roles in the metabolism or physiology of animals. Vitamin D is precursor to a hormone that regulates
calcium metabolism. Vitamin A furnishes the visual pigment of the vertebrate eye and is a regulator of gene expression during epithelial cell growth. Vitamin E functions in the protection of membrane
lipids from oxidative damage, and vitamin K is essential in the blood-clotting process.
■ Ubiquinones and plastoquinones, also isoprenoid derivatives, are electron carriers in mitochondria
and chloroplasts, respectively.
■ Dolichols activate and anchor sugars to cellular membranes; the sugar groups are then used in the synthesis of complex carbohydrates, glycolipids, and glycoproteins.
■ Lipidic conjugated dienes serve as pigments in flowers and fruits and give bird feathers their striking colors.
■ Polyketides are natural products widely used in medicine.