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This article discusses the biomedical importance of lipids, including their role as dietary constituents, energy sources, and components of cell membranes. It also explores the classification of lipids, such as simple lipids, complex lipids, and precursor and derived lipids. Additionally, it covers the significance of unsaturated fatty acids, phospholipids, glycolipids, and steroids in physiological processes and disease development. The text language is English.
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Lipids Lipids of Physiologic Significance
BIOMEDICAL IMPORTANCE • The lipids • The common property • insoluble in water • soluble in nonpolarsolvents • They are important dietary constituents • high energy value • fat-soluble vitamins • essential fatty acids • Fat is stored in adipose tissue
BIOMEDICAL IMPORTANCE • Thermal insulator • electrical insulators • cellular constituents • Membranes • Transport • Lipoproteins • Lipid biochemistry is necessary • obesity, diabetes mellitus, atherosclerosis, polyunsaturated fatty acids in nutrition and health
Classification • Simple lipids • Esters of fatty acids with various alcohols • Complex lipids • groups in addition to an alcohol and a fatty acid • Phospholipids • Glycerophospholipids • Sphingophospholipids • Glycolipids • Other complex lipids • Sulfolipids and aminolipids • Lipoproteins
Classification • Precursor and derived lipids • Neutral lipids • acylglycerols (glycerides),cholesterol, and cholesteryl esters
Free fatty • Free fatty acids • Saturated • -anoic • Unsaturated • -enoic • 1,2,3,… • α, β, γ ,… ω or n carbons • Δ
Unsaturated Fatty Acids • Monounsaturated • Polyunsaturated • Eicosanoids • eicosa- (20-carbon) polyenoic fatty acids • Prostanoids • Prostaglandins(PGs) • Prostacyclins (PGIs) • Thromboxanes (TXs) • Leukotrienes (LTs) • Lipoxins (LXs)
Prostaglandins • The number of double bonds • PG1, PG2, PG3 • Different substituent groups (on ring) • A, B,C,etc
The leukotrienes andlipoxins • Lipoxygenase pathway • three or four conjugated double bonds • Leukotrienes cause bronchoconstriction as well as being potent proinflammatoryagents and play a part in asthma
Unsaturated Fatty Acids • Geometric isomerism • Cis • on the same side • Trans • if on opposite sides • as a by-product of the saturation of fatty acids • ingestion of ruminant fat • Significance • Molecular packing in membranes
Unsaturated fatty acids of physiologic and nutritional significance
Structure of some unsaturated fatty acids
Physical and Physiologic Propertiesof Fatty Acids • Chain Length and Degree of Unsaturation • even-numbered-carbon fatty acids • The melting points
TRIACYLGLYCEROLS (TRIGLYCERIDES) • THE MAIN STORAGE FORMS OF FATTY ACIDS • Mono- and diacylglycerols
PHOSPHOLIPIDS • MAIN LIPID CONSTITUENTS OF MEMBRANES • derivatives of phosphatidic acid • Phosphatidylcholines (Lecithins) • the most abundant phospholipids of the cell membrane • represent a large proportion of the body’s store of choline
PHOSPHOLIPIDS • Surfactant • Dipalmitoyl lecithin • respiratory distress syndrome • Phosphatidylethanolamine (cephalin) • Phosphatidylserine • Phosphatidylinositol • Cardiolipin
Phospholipids • Plasmalogens
GLYCOLIPIDS • GLYCOSPHINGOLIPIDS • NERVE TISSUES • CELL MEMBRANE • Galactosylceramide • Sulfatide • Sulfogalactosylceramide • Glucosylceramide • Glycosphingolipid of extraneural tissues
Simple glycosphingolipids • Complex glycosphingolipids • Gangliosides • Sialic acid • The simplest ganglioside found in tissues is GM3 • Functions • Receptor, …
STEROIDS • Cholesterol • Atherosclerosis • As Precursor • Sterol • Has one or more hydroxylgroups and no carbonyl orcarboxyl groups
Stereoisomers • “Chair” or a “boat” form • The rings can be either cis or trans • β bonds • above the plane of the rings • α bonds • bonds attaching groups below
Cholesterol • Cholesteryl ester
Ergosterol • Precursor of Vitamin D
Polyprenoids • Synthesized from five-carbon isoprene units • Include • Ubiquinone • Dolichol • Vitamins • A, D, E, and K, and β-carotene (provitamin A)
LIPID PEROXIDATION • A SOURCE OF FREE RADICALS • Lipids exposed to oxygen • deterioration of foods (rancidity) • damage to tissues • Cancer, inflammatory diseases, atherosclerosis, and aging • Peroxide formation from fatty acids containing methylene-interrupted double bonds • Antioxidants • Vitamin E, Beta-carotene • Urate and vitamin C
AMPHIPATHIC LIPIDS • Form • Membranes, Micelles, Liposomes, & Emulsions • Contain polar groups • Fatty acids, phospholipids, sphingolipids, bile salts, and, to a lesser extent, cholesterol • Part of the molecule is hydrophobic, and part is hydrophilic
Micelles • When a critical concentration of these lipids is present in an aqueous medium • Facilitating absorption of lipids • Liposomes • Formed by sonicating an amphipathic lipid in an aqueous medium • as carriers of drugs
Emulsions • Much larger particles
Waxes • Serve as • Energy Stores and Water Repellents • Esters of long-chain (C14 to C36) saturated and unsaturated fatty acids with long-chain (C16 to C30) alcohols • Their melting points (60 to 100 °C) are generally higher than those of triacylglycerols