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

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

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)

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

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

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 Fish oils, nuts, seeds and oils

OBJECTIVES State the biological significance of fats 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

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)

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.

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

Vitamin A,D,E,K fat soluble vitamins 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) Supply essential fatty acids Nervous system: Rich in lipids

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

Classification of Lipids 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)

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

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

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

OBJECTIVES Define chemical composition of fats 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

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

Chemical composition of lipids

OBJECTIVES Define physical properties of fats 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

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 (acidic-yellow color (hydrolysis & oxidation)

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)

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)

OBJECTIVES Define chemical properties of fats 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

Chemical Properties of Fats Acrolein Formation – glycerol  heat + potassium bisulphate Hydrogenation – unsaturated fats (+nickel-catalyst) – 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)

OBJECTIVES Classify lipids into fatty acids, triglycerides, steroids 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

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

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 (C57H110O6) building blocks are 1 glycerol and 3 fatty acids per molecule saturated and unsaturated

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)

OBJECTIVES Define phospholipids 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

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

OBJECTIVES Describe the chemistry and functions of cholesterol 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

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

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

Functions of Cholesterol Diabetes Mellitus Atherosclerosis Plaque around The artery Hardening & Narrowing Myxoedema (Hypothyroidism) CHOLESTEROL Hyperthyroidism Xanthomatosis (fat storage disorder) Obstructive jaundice Nephrotic syndrome (kidney disorder)

OBJECTIVES Explain lipoproteins 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

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.

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

Lipoproteins according to Density Type Density g/ml Protein Triglycerides (TAG) Cholesterol Phospholipids Free Ester Chylomicrons < 0.95 1 85-95 1-2 3-6 Very low density lipoprotein VLDL 0.95-1.006 10 50-60 4-8 15-20 Low density lipoproteins LDL 1.006-1.063 22 38 20 High density lipoproteins HDL 1.063-1.21 45-60 3 5 25-30

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?

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