Biochemistry Lipids PDF

## Lipids 1 ***Definition:*** Lipids are defined as a heterogeneous group of organic compounds characterized by: 1. Their relative insolubility in water. 2. Their solubility in non-polar organic solvents such as ether chloroform or benzene. ***Classification of Lipids:*** * **Simple lipids:...

## Lipids 1 ***Definition:*** Lipids are defined as a heterogeneous group of organic compounds characterized by: 1. Their relative insolubility in water. 2. Their solubility in non-polar organic solvents such as ether chloroform or benzene. ***Classification of Lipids:*** * **Simple lipids:** * Fats: esters of fatty acids with glycerol. Oils are fats in the liquid state. * Waxes: esters of fatty acids with higher molecular weight monohydric alcohols. * **Complex lipids:** * Phospholipids: lipids containing in addition to fatty acids and alcohol, a phosphoric acid residue. * Glycerophospholipids: the alcohol is glycerol. * Sphingophospholipids: the alcohol is sphingosine. * **Precursor and derived lipids:** ***The structures, the acylglycerols .R indicates a linear aliphatic chain*** **Sphingophosolipids** sphingosine is linked with fatty acids forming ceramides in plants and animal tissue. * Sphingomyelins are phosphocholine attached to the ceramide. **Functions of phospholipids** Phospholipids are present in every body cell with abundance in nerve cells, brain and muscles. * They are major constituents of cell and mitochondrial membranes. ***This is the structure of ceramide. The portion of ceramide shown in red is sphingosine.*** **Glycolipids (glycosphingolipids):** * They are lipids containing fatty acids, sphingosine and carbohydrate. * Glycolipids (Cerebrosides and gangliosides): * They are carbohydrate derivatives of ceramides. * If the carbohydrate residue is of a monosaccharide, the glycolipid is called a simple glycolipid. Cereborosides are simple glycolipids containing the sugars D.galactose or D. glucose. **Gangliosides:** * They are complex glycolipids containing more than one monosaccharide attached to the ceramide. * Gangliosides are abundant in brain. They act as receptors at cell membrane. **Other complex lipids:** * Sulpholipids, aminolipids and lipoproteins * Sulpholipids: They are sulphate cerebosides. The sulphate group is attached to the sugar moiety. ***This is a continuation of the previous slide. Different groups are added to the hydroxyl portion of ceramide to form sphingomyelin, cerebrosides, and gangliosides. NANA, N-acetylneuraminic acid, also called sialic acid; Gic, glucose; Gal, galactose; GalNac, N-acetylgalactosamine. The structures, the acylglycerols, and the names of the groups are shown in the diagram.*** ***Select this paragraph to edit*** ## Lipids 2 ### 3. Precursor and Derived Lipids: * This is a heterogeneous group composed of the hydrolysis products of simple and complex lipids. * These include: fatty acids, glycerol, alcohols, fatty aldehyde and ketone bodies. Ketone bodies include acetone, acetoacetate, and ẞ-hydroxybutarate * The group also includes other substances, which are insoluble in water but soluble in fat solvents such as steroids, and, fat soluble vitamins, etc. * Alcohol in lipids include: glycerol, cholesterol, sphingosine and ergosterol ### The structures of fatty acids, & glycerol. Fatty acids shown are; palmitc, oleic and stearic. Fatty acids are identified by the number of carbons and the number of double bonds and their positions (e.g., 18:1, 19). ### precursor lipids #### The fatty acids of lipids: The naturally occurring fatty acids of lipids are straight, long chain monocarboxylic acids with even numbered carbons. * Examples of saturated fatty acids are palmitic acid (16C) and stearic acid (18C) * Example of unsaturated fatty acids are, Linoleic acid (2;18C), linolenic acid (3;18C) and arachidonic acid(4:20C) * All naturally occurring fatty acids have double bonds in the cis configuration. #### Alcohols of lipids * **Cholesterol:** It is present in all animal tissues especially liver, kidney adrenal cortex, brain and nerves. It is the precursor of steroid hormones, bile salts and vitamin D,. it is a component of cell membrane. * **Ergosterol:** It is a plant sterol that gives vitamin D₂ by U.V. light. * **Sphingosine:** It is an amino alcohol. * **Glycerol:** It is the alcohol of simple lipids. ### Derived lipids **Eicosanoids:** * These are compounds derived from arachidonic acid (20.C). * These compounds include prostanoids and leukotrienes (LT). * Prostanoids comprise prostaglandins (PG), prostacyclins (PC)and thromboxane (TX). * Eicosanoids are almost present in every body cell. * They have important physiological functions. **Steroids:** * Cholesterol is the precursor of all classes of steroid hormones. * They contain side chain which differs from one steroid to another. * The following representative examples of steroids: Cortisone, Testosterone, Progesterone, estrogen and aldosterone **Sodium Glycocholate:** * It is a bile salt important for digestion and absorption of lipids. **Progesterone:** * It is a female sex hormone. **Testosterone:** * It is a male sex hormone. **Cortisone:** * It is a glucocorticoid hormone that controls the metabolism of carbohydrates, protein and fat. ***Select this paragraph to edit***