UNIT 3 CHEMISTRY OF LIPIDS OBJECTIVES Define lipids

UNIT 3 CHEMISTRY OF LIPIDS

OBJECTIVES • • • Define lipids and its occurrence State the biological significance of fats Define chemical composition of fats Define physical properties of fats Define chemical properties of fats Classify lipids into fatty acids, triglycerides, steroids Define phospholipids Describe the chemistry and functions of cholesterol Explain lipoproteins 2

OBJECTIVES • Define lipids and its occurrence • • State the biological significance of fats Define chemical composition of fats Define physical properties of fats Define chemical properties of fats Classify lipids into fatty acids, triglycerides, steroids Define phospholipids Describe the chemistry and functions of cholesterol Explain lipoproteins 3

What are Lipids? • Group of naturally occurring substances • Consists of higher fatty acids • Insoluble in water • Soluble in: Ether, chloroform, benzene and acetone (organic solvents) 4

What are Lipids? • LIPIDS: Fatty acids, Triacylglycerols, Ketone bodies, Cholesterol, Phospholipids & Sphingolipids • “Fats” and “Oils” – crude lipid mixtures from natural sources. • Fats (solid) & Oil (liquid) at room temperature 5

Occurrence of Lipids? • Widely distributed in plants and animals. • Plants: nuts, seeds and oils • The Nervous system of Animals: cholesterol, phospholipids and glycolipids • Blood: contains lipoproteins 6

Occurrence of Lipids? • Fat depots (large amount of fats): – Subcutaneous tissues – Mesenteric tissues – Fatty tissues around the kidney – Yellow bone marrow • Food sources: – Milk, Egg, Meat, Liver 7

OBJECTIVES • Define lipids and its occurrence • State the biological significance of fats • • Define chemical composition of fats Define physical properties of fats Define chemical properties of fats Classify lipids into fatty acids, triglycerides, steroids Define phospholipids Describe the chemistry and functions of cholesterol Explain lipoproteins 8

Biological Significance of Fats Acts as fuel in the body. (caloric value: 9 Kcals/gm) Deposits of fats underneath the skin = exert insulating effects. The mesenteric fat around organs (kidney) = padding and protecting internal organs. Building materials. (cholesterol – hormone synthesis) 9

Biological Significance of Fats Lipids supply the essential fatty acids which cannot be synthesized in the body. . The Nervous system is particularly rich in lipids. Vitamins A, D, E and K are fat soluble. ( lipid/fat is needed for absorbing these vitamins) Lipoproteins and phospholipids are important constituents of cell wall & mitochondria. 10

Biological Significance of Fats • Adult: ingests 60 -150 g of lipids per day of which 90% is triacylglycerol (TAG). • Balance: cholesterol, cholestryl, esters, phospholipids and free fatty acids (FFA) 11

Lipoprotein & Phospholipids (cell wall & mitochondrion constituents) Acts as fuel in the body Insulating effect Padding & protection of internal organs Vitamin A, D, E, K fat soluble vitamins Building Materials (hormones ) Nervous system: Rich in lipids Supply essential fatty acids 12

Classification of Lipids LIPIDS Simple Lipids Compound Lipids Derived Lipids Substances Associated with Lipids 13

Classification of Lipids Classification Definition Examples Simple Lipids Esters of fatty acids with various alcohols * Neutral fats (F. A. + alcohol) * Glycerol (alcohol in fats) * Anything other than glycerol (alcohol in waxes) 14

Classification of Lipids Classification Compound Lipids Description 4 Sub-Divisions Contains other chemical • Phospholipids groups in addition to alcohol • Glycolipids and fatty acids • Sulpholipids • Lipoprotein • Phospholipids • Contains fatty acids, glycerol, phosphoric acid & nitrogenous compound (lecithin, cephalin) • Glycolipids • Lipids + carbohydrate + nitrogen but no phosphoric acid & glycerol • Sulpholipids • Lipids containing sulphate groups • Lipoprotein • Attached to proteins (present in plasma & tissues) 15

Classification of Lipids Classification Description Derived Lipids Substances derived from simple & compound by hydrolysis. Examples • Fatty acids Derived Lipids • Alcohols other than glycerol • Glycerides • Bases (choline, serine) 16

Classification of Lipids Classification Examples • Carotenoids Substances • Tocopherols Associated with Lipids • Vitamins A, D, E and K • Steroids (Cholesterol) 17

OBJECTIVES • • Define lipids and its occurrence State the biological significance of fats • Define chemical composition of fats • • • Define physical properties of fats Define chemical properties of fats Classify lipids into fatty acids, triglycerides, steroids Define phospholipids Describe the chemistry and functions of cholesterol Explain lipoproteins 18

Chemical Composition of Fats ANIMALS AND VEGETABLE FATS Complex mixtures of glycerides Esters of glycerol & fatty acids Triglyceride s (TAG)Neutral fats 3 molecules of fatty acids - glycerol One molecule of glycerol + 3 molecules of fatty acids (condensation) 19

Chemical composition of lipids

OBJECTIVES • • • Define lipids and its occurrence State the biological significance of fats Define chemical composition of fats • Define physical properties of fats • • • Define chemical properties of fats Classify lipids into fatty acids, triglycerides, steroids Define phospholipids Describe the chemistry and functions of cholesterol Explain lipoproteins 21

Physical Properties of Fats • Greasy to touch and leaves an oily impression on paper. • Are insoluble in water but soluble in organic solvents. • Have less specific gravity than water (solid fat= 0. 86), (liquid fat = 0. 95) • Pure glycerides are tasteless, odorless, colorless and neutral in reaction (acidicyellow color (hydrolysis & oxidation) 22

Physical Properties of Fats • Flavor of butter is due to the presence of bacterial flora; color of butter, human fat and egg yolk (due to presence of carotene & xanthophil). • Hardness and consistency depends on the amount of saturated and unsaturated fatty acids present. Saturated fatty acids are solid (room temperature) while Unsaturated fatty acids are liquid (room temperature) (e. g. oils) 23

Physical Properties of Fats • Fats have definite melting points. • When liquid fat is placed on water- it spreads uniformly over the surface of water. If the quantity is small – it forms a layer of 1 molecule thickness (effect: to lower surface tension- help transport fat) • Though fat is insoluble in water- can be broken down into minute droplets and dispersed in water (emulsification) 24

OBJECTIVES • • Define lipids and its occurrence State the biological significance of fats Define chemical composition of fats Define physical properties of fats • Define chemical properties of fats • • Classify lipids into fatty acids, triglycerides, steroids Define phospholipids Describe the chemistry and functions of cholesterol Explain lipoproteins 25

Chemical Properties of Fats • Acrolein Formation – glycerol heat + potassium bisulphate • Hydrogenation – unsaturated fats (+nickelcatalyst) – saturated fats (“hardening”) e. g vegetable oil – commercial cooking oil • Saponification – hydrolysis of fat by alkali (glycerol + alkali salts = soap) • Rancidity – chemical change resulting in unpleasant odor and taste on storage when fats are exposed to light, heat, air and moisture. – E. g. Ascorbic acid (Vitamin C) and Vitamin E are antioxidants (prevents rancidity) 26

OBJECTIVES • • • Define lipids and its occurrence State the biological significance of fats Define chemical composition of fats Define physical properties of fats Define chemical properties of fats • Classify lipids into fatty acids, triglycerides, steroids • • • Define phospholipids Describe the chemistry and functions of cholesterol Explain lipoproteins 27

Essential Fatty Acids (Polyunsaturated Fatty Acids) Lipids Examples • Linoleic acid Polyunsaturated Fatty Acids • Linolenic acid Sources • Linseed • Cotton seeds • Peanuts • Corn oils • Arachidonic acid (not synthesized by the body- must be taken in the diet) • Linoleic acid – the only fatty acid which is absolutely indispensable. 28

Triglycerides • Neutral fat • Concentrated source of energy • used primarily for energy; most common lipid in the body • contain C, H, and O but less O than carbohydrates (C 57 H 110 O 6) • building blocks are 1 glycerol and 3 fatty acids per molecule saturated and unsaturated 29

What are Steroids? • Are non-saponifiable lipids • Are biological compounds with diverse physiological activities • Are compounds having a cyclopentanoperhydrophenanthrene ring system • Has only a hydroxyl group (-OH) as its functional group (sterol, e. g. cholesterol) 30

OBJECTIVES • • • Define lipids and its occurrence State the biological significance of fats Define chemical composition of fats Define physical properties of fats Define chemical properties of fats Classify lipids into fatty acids, triglycerides, steroids • Define phospholipids • • Describe the chemistry and functions of cholesterol Explain lipoproteins 31

What are Phospholipids? • Lipids containing phosphorus • Are good emulsifying agents • Found in cell membranes and in subcellular structures (lipid & water interaction) 32

OBJECTIVES • • Define lipids and its occurrence State the biological significance of fats Define chemical composition of fats Define physical properties of fats Define chemical properties of fats Classify lipids into fatty acids, triglycerides, steroids Define phospholipids • Describe the chemistry and functions of cholesterol • Explain lipoproteins 33

What is Cholesterol? • Are light yellow crystalline solid • Are soluble in chloroform and other fat solvents • Polyunsaturated acids – lower the plasma cholesterol level • The most abundant lipid in the human body Are synthesized in the liver, adrenal cortex, intestines, testes and skin. Play an important role as a component of biomembranes and has a modulating effect on the fluid state of the membrane. Can be estimated by color reactions (e. g. Liebermann. Burchard reaction) – blue or green color 34

Functions of Cholesterol • An important tissue component (modulating effect, integrity & permeability) • Play an important role in insulating nerves and brain structure • For transport of fatty acids in the body • It is a part of lipoproteins It neutralizes the hemolytic action of various agents such as venom, bacterial toxins It gives rise to “provitamin D” It is a precursor of cholic acid in the body as also bile salts. It gives rise to sex hormones 35

Functions of Cholesterol Atherosclerosis Plaque around The artery Hardening & Narrowing Diabetes Mellitus Myxoedema (Hypothyroidism ) CHOLESTERO L Hyperthyroidis m Obstructive jaundice Xanthomatosi s (fat storage disorder) Nephrotic syndrome (kidney disorder) 36

OBJECTIVES • • Define lipids and its occurrence State the biological significance of fats Define chemical composition of fats Define physical properties of fats Define chemical properties of fats Classify lipids into fatty acids, triglycerides, steroids Define phospholipids Describe the chemistry and functions of cholesterol • Explain lipoproteins 37

What are Lipoproteins? • Are conjugated proteins involved in transport and delivery of lipids to tissues. E. g. Lipids (Cholesterol & triglycerides) + water soluble carrier proteins • It transport neutral lipids in the blood. • It has lower density than the ordinary protein molecule. 38

Distribution of Lipoproteins: Body tissues Nucleus, Mitochondria Microsome Thromboplastin (prothrombin) Egg yolk (HDL & LDL) Cell membranes LIPOPROTEINS Plasma Cholesterol, Phospholipids, neutral fat, traces of fat soluble vitamins Steroid hormone Rhodopsin (combination of protein, opsin and retinal aldehyde of Vit. A Fat droplets in milk 39

Lipoproteins according to Density Type Density g/ml Protein Triglycerides (TAG) Cholesterol Free Ester Phospholipids Chylomicron s < 0. 95 1 85 -95 1 -2 3 -6 Very low density lipoprotein VLDL 0. 951. 006 10 50 -60 4 -8 10 15 -20 Low density lipoproteins LDL 1. 0061. 063 22 10 10 38 20 High density lipoproteins HDL 1. 0631. 21 45 -60 3 5 15 -20 25 -30 40

EVALUATION • • • Give at least 3 importance of lipids. What are the 4 major groups of lipids? Give 2 examples of lipids? What are the functions of cholesterol? Differentiate steroid from cholesterol? Name 3 physical properties of fats? 41

SPECIAL THANKS TO: Sir Norman, Sir Joven, Ms. Grace 42