Biomolecule Lipids Lecture 6 Dr. Aparna Islam 1

What are Lipids? LIPID describes a chemically varied group of fatty substances and are highly concentrated energy stores. They are esters of long chain fatty acids and alcohols. They are water-insoluble bio-molecules but soluble in organic solvents such as ether, benzene, chloroform, etc. 2

3 Lipids serve as fuel molecules, signal molecules, and components of membranes, hormones and intracellular messengers.

Based on there Biological functions, lipids can be classified into: Storage Lipids– The principle stored form of energy Structural Lipids– The major structural elements of Biological Membranes Signals– Lipids are hormones, cofactors and pigments Classification of Lipids 4

Based on there chemical composition lipids can be classified into: 1.SIMPLE LIPIDS: These lipids are the esters of fatty acids with alcohols. They are of three types: Waxes, sterol esters and Triacylglycerol. 2.COMPOUND/COMPLEX LIPIDS: These lipids are esters of fatty acids with alcohols with additional groups such as phosphate, nitrogenous base, etc. They are again divided into 3 types: Phospholipids, Glycero-phosphlipids, Sphingo-phospholipids. 5

3. DERIVED LIPIDS: These lipids are obtained on hydrolysis of simple and complex lipids. These lipids contain glycerol and other alcohols. This class of lipids include steroid hormones, ketone bodies, hydrocarbons, fatty acids, fatty alcohols, mono and di-glycerides. 4. MISCELLANEOUS LIPIDS: These include compounds which contain characteristics of lipids. They include, squalene, terpenes, hydrocarbons, carotenoid etc. 6

Lipids Simple 1.Wax esters 2.Sterol esters 3.Triacylglycerol Complex Derived 1.Fatty acids 2.Sterols 3.Diglycerides 4.monoglycerides Phospholipids Glycolipids 1.Cerebrosides 2.Gangliosides Glycerophospholipids 1.Phosphatidylcholine (PC) 2.Phosphatidylethanolamine (PE) 3.Phosphatidylinositol (PI) Sphingolipids 1.Ceramides 2.Sphingomyelin 7

A molecule of glycerol is made up of three carbon atoms. Each of these C has a hydroxyl group attached to it. Hydrogen atoms occupy the remaining positions. Glycerol 8

Fatty Acids (from Fats and Oils) A single fatty acid molecule contains an acid (COOH) group attached to a hydrocarbon chain. Hydrocarbon usually denoted by the letter ’R’. Fatty acids are composed only of carbon, hydrogen and oxygen in the proportion of 76%, 12.6% and 11.3% respectively. Hydrocarbon chains in fatty acids ranging from

Saturated = If every carbon atom in the chain is joined by a single C-C bond. Unsaturated = at least one C=C bond. Oleic (C 18 with one C=C) and linolenic (C 18 with 3 C=C) are the most abundant unsaturated Polyunsaturated = many double bonds. Most animal fats are saturated while most plant fats are unsaturated Types of fatty acids 10

Triglycerides (TAGs) A triglyceride molecule is made of a glycerol molecule and three fatty acids. Most occurring TAGs are mixed, which contain two or more different fatty acids. TAGs are non polar, hydrophobic molecules, essentially insoluble in water. Almost all fatty acids have even number of carbon atoms(12 to 24); 11

The molecules join together through the process of condensation losing a molecule of water each time a link is made. The link between the glycerol molecule & each fatty acid is an ‘Ester Link’. The fatty acids in a lipid molecule can differ in length and can be saturated or unsaturated. Triglycerides (TAGs) formation Common formula of TAGs 12

Phospholipids In phospholipids one of the fatty acids of a triglyceride is substituted by a phosphate group. Phosphoglycerides comprise the major lipid component of cell membranes Nonpolar tails aggregate in the center of a bilayer Ionic head is exposed to solvent 13

Phospholipids are degraded in Lysosome by specific enzymes, Phospholipases The enzymes that degrade phospholipids 14

Storage Lipids Fats and oils (Triacylglycerols) are composed of 3 fatty acids each in ester linkage with a single glycerol Its also called neutral fat. They are stored in adipocytes in animals and endosperm and cotyledon cells in plants. A mammal contains 5% to 25% or more of its body weight as lipids,90%TAG 15

Fats Stored in Animal and Plant Cells 16

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Waxes are esters of long-chain(C14-C36) saturated and unsaturated fatty acids with long chain (C16-C30) alcohols. Storage Lipids Wax 18

Functions of Wax Chief storage fuels for some of the microorganisms. Protect skin and hair. Prevents excess water evaporation in plants. Protects against parasites Application in industries such as, pharmaceuticals, and cosmetics 19

Lipids as structural elements 20

CLASSIFICATION OF LIPIDS AS STRUCTURAL ELEMENTS

Glycerol Phosphate 22

The type of fatty acid that connects to L-glycerol phosphate 3 Phosphate are specific for different organisms, different tissues of the same organisms, and different glycerophospholipids in the same cells and tissues. General structure of Glycerophospholipid 23

Galactolipids 24

Steroids Steroids,are another class of lipid, defined by structure Has four fused rings A, B, C, and D, beginning at the lower left Carbon atoms are numbered beginning in the A ring 25

Functions of Steroids In humans as hormones, steroids are chemical messengers secreted by glands and carried through the bloodstream to target tissues Also widely distributed as cholesterol 26

Male Sex Hormones Testosterone and androsterone are the two most important male sex hormones or androgens 27

Estrone and estradiol are the two most important female sex hormones or estrogens Progesterone is the most important progestin, steroids that function in pregnancy Female Sex Hormones 28

Adrenocortical steroids: secreted by the adrenal glands near the upper end of each kidney Glucocorticoids: regulation of glucose metabolism and in the control of inflammation Other Steroid Hormones Made in pharmaceutical laboratories as new drugs, includes oral contraceptives Synthetic Steroids 29

Cholesterol Cholesterol is a derived lipid. Its widely distributed as sterols in animals and humans Most of the cholesterol is synthesized by the liver Its an essential component of cell membrane Vit. D, hormones and bile acids are synthesized from cholesterol. Bile acids act as detergents in the intestine. These are essential for normal digestion and absorption of fats and fat-soluble vitamins by act as detergents in the intestine An increase in dietary intake of cholesterol, increases its deposition in the body as well which leads to coronary heart diseases. Unsaturated fats reduce the level of cholesterol in blood. 30

Low density lipoproteins (LDL) transports cholesterol from liver through blood to the tissues (Bad cholesterol), thus High risk of heart attack High density lipoprotein (HDL) transports cholesterol from blood to the liver where it is metabolized (Good cholesterol), Low risk of heart attack 31

32 Soap A mixture of sodium or potassium salts of long-chain fatty acids produced by alkaline hydrolysis (saponification) of animal fat with alkali

33 Cleansing Action of Soap The carboxylate end of the long-chain molecule is ionic and therefore is preferentially dissolved in water The hydrocarbon tail is nonpolar and dissolves in grease and oil Soaps enable grease to be dissolved into water

Lipids are the constituents of cell membrane and regulate membrane permeability. They protect internal organs, serve as insulating materials and give shape and smoothness to the body. They serve as a source of fat soluble vitamins. Essential fatty acids are useful for transport of cholesterol, formation of lipoproteins, etc. Functions of Lipids 34

Phospholipids in mitochondria are responsible for transport of electron transport chain components. Accumulation of fat in liver is prevented by phospholipids. Phospholipids help in removal of cholesterol from the body by participating in reverse cholesterol transport. Cholesterol is a constituent of membrane structure and it synthesizes bile acids, hormones and vitamin D. It is the principal sterol of higher animals, abundant in nerve tissues and gallstones 35