Lipids Chemistry 2024 PDF

LIPIDS Dr. Mohammed Amanullah  LIPIDS  Lipidsare group of compounds related directly or indirectly to fatty acids.  They are insoluble in water  Soluble in fat solvents like ether and benzene.  They are important dietary constituents providing: (a) High energy value ( 1 g = 9...

LIPIDS Dr. Mohammed Amanullah  LIPIDS  Lipidsare group of compounds related directly or indirectly to fatty acids.  They are insoluble in water  Soluble in fat solvents like ether and benzene.  They are important dietary constituents providing: (a) High energy value ( 1 g = 9 kcal) (b) Fat soluble vitamins 1g 4 kcal Protein (c) Essential fatty acids. carbohydrates  FATTY ACIDS  They are the monocarboxylic acids with a long hydrocarbon chain. 0 lastcarbon omegacarbon  There are two types of fatty acids (1) Saturated fatty acids If check (2) Unsaturated fatty acids.  Saturated fatty acids  These fatty acids contain only single bonds along the length of the carbon chain, i.e., all the carbon atoms are fully saturated with hydrogen atoms. 01409.0  Thefatty acids found in the human body contain even number (4, 6, 8, …) of carbon atoms. AI T.SI.ws  saturated fatty acid III 20 O at www.wiewd Ct 2 TH COOH  Unsaturated fatty acids  These fatty acids contain one or morePoints iii e double bonds in the hydrocarbon chain.  They are further classified depending upon the number of double bonds present per fatty acid as a) Monounsaturated fatty acids: one double bond per fatty acid b) Polyunsaturated fatty acids: two or more double bonds  7 Numbering of carbon atoms and location of the double bonds Carbon atoms in FAs are numbered from the carboxyl carbon (carbon No. 1.) The carbon atoms adjacent to the carboxyl carbon (carbon 2,3,4) are also known as α,β,γ respectively. The terminal methyl carbon is known as the ω-carbon or the n-carbon. T omega The site of unsaturation is indicated by the symbol Δ  Δ9 indicates double bond between 9 and 10 carbon atoms. CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 COOH 9(ω) 8 7 6 5 4(γ) 3(β) 2(α) 1 FA CONTD…  A second system starts the counting from the omega carbon, the last carbon of the chain (omega is the last letter of the Greek alphabet).  ω9 indicates the double bond on the ninth carbon counting from the ω carbon.  In animals, additional double bonds are introduced only between the existing double bond and the carboxyl carbon, leading to three series of fatty acids known as ω3, ω6 and ω9 8 UNSATURATED FA of SIGNIFICANCE-I No. of Carbon Family Common name atoms & No. of double bonds Monoenoic acids [One double bonds] 16:1 ω7 Palmitoleic 18:1 ω9 Oleic 18:1 ω9 Elaidic Dienoic acids [Two double bonds] 18:2 ω6 Linoleic Trienoic acids [Three double bonds] 18:3 ω6 γ-Linolenic 18:3 ω3 α-Linolenic 9  UNSATURATED F.A.of SIGNIFICANCE-II No. of Carbon Family Common name Occurence atoms & No. of double bonds Tetraenoic acids [Four double bond] ω6 Found in animal 20:4 Arachidonic fats. Important component of phospholipid in animals Pentaenoic acids [Five double bond] ω3 Important 20:5 Timnodonic component of fish oils Hexaenoic acids [Six double bond] ω3 Fish 22:6 Cervonic oils;phospholipids in brain 10 Classification of lipids: CLASSIFICATION OF LIPIDS 1.SIMPLE LIPIDS: Esters of fatty acids (FA) with various glycerol a. Fats: esters of FA with glycerol b. Waxes: esters of FA with higher molecular weight alcohols 2. COMPLEX LIPIDS: Esters of FA containing groups in addition to an alcohol and a FA a. Phospholipids: Esters of FA with alcohol and phosphoric acid. In glycerophospholipids the alcohol is glycerol with different bases. Ex. choline or lecithin, ethanolamine or cephalin, serine, inositol In sphingophospholipids the alcohol is sphingosine 12 CLASSIFICATION CONTD….. b. Glycolipids are lipids with carbohydrates and sphingosine. i. Glucocerebrosides: Has glucose ii. Galactocerebrosides: Has galactose iii.Gangliosides: Have several sugar units c. Others complex lipids are lipoproteins: Chylomicrons, VLDL, LDL & HDL 3. DERIVED LIPIDS: These include FA, glycerol, steroids, some alcohols, fatty aldehydes and ketone bodies. 13 Steroids  Allcompounds containing the cyclo-pentano- perhydro-phenanthrene ring are called steroids.  The most abundant steroids in the human body are the sterols, i.e., an alcohol (–OH) group is attached to the steroid nucleus. e.g., cholesterol, ergosterol, bile acids, sex hormones, adrenal cortical hormones and vitamin D3.  Cholesterol is the major sterol in the body. It is a constituent of cell membrane and provides rigidity to it.  Cholesterol acts as the precursor for all the other steroids in the body, viz., testosterone, estrogen, progesterone, vitamin-D, bile salts, corticosteroids, etc. Eicosanoids 16 These are compounds derived from eicosa (20C) polyunsaturated fatty acid the “arachidonic acid”. They comprise: 1. Prostanoids:- prostaglandins (PGs), prostacyclins (PGIs), Thromboxanes (TXs) 2. Leukotrienes (LTs) 3. Lipoxins (LXs) Prostaglandins have important physiologic and pharmacologic activities in the human body. Leukotrienes cause bronchoconstriction and play an role in asthma. 16  Chemical properties of lipids: 1. Saponification: Hydrolysis of TAG with KOH or NaOH is called saponification or soap formation. 2. Rancidity: Fats contaminated with enzymes like lipase undergo partial hydrolysis and oxidation of unsaturated fatty acids at the double bonds. This is even brought about by the atmospheric moisture and temperature.  Due to this, there is release of hydrogen peroxide giving a bad odour and taste to the fat.  This fat is said to be rancid and the process is known as rancidity.  Rancidity can be prevented by antioxidants like vitamin E, vitamin C, phenols, hydroquinones, etc. CELL MEMBRANE AND CELL MEMBRANE LIPIDS 18 18 Cell membrane Membranes are complex structures composed of lipids, proteins, & carbohydrates. The basic structure of cell membranes is the lipid bilayer. This bilayer is formed by two sheets of phospholipids in which the hydrophilic polar head groups are directed away from each other and are exposed to the aqueous environment on the outer and inner surfaces of the membrane. The hydrophobic nonpolar tails of these molecules are oriented toward each other, in the direction of the center of the membrane. 19 19 Membrane / Micelle 20 20  The Cell Membrane Polar Head Phospholipid Nonpolar Tail Phospholipids join a bilayer to form a cell membrane. 21 21 The Cell Membrane Glycolipid Phospholipids join a bilayer to form a cell membrane. 22 22 Cell membrane lipids A. PHOSPHOLIPIDS are the predominant lipids of cell membranes. Phospholipids containing choline are the most abundant phospholipids of the cell membrane. Phosphatidylinositol 4,5-bisphosphate is an important constituent of cell membrane phospholipids. Glycolipids and cholesterol are also important components of the cell membrane. 23 23