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

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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

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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)

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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

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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 lipoproteins6

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

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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

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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)

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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.

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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)

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Lipoprotein & Phospholipids

(cell wall & mitochondrion constituents)

Vitamin A,D,E,K

fat soluble

vitamins

Acts as fuel in the body

Supply essential fatty

acidsNervous system:

Rich in lipids

Building Materials(hormone

s)

Padding & protection of

internal organs

Insulating effect

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Classification of Lipids

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LIPIDS

Simple Lipids

Substances Associated with Lipids

Derived Lipids

Compound Lipids

Classification of Lipids

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Classification Definition Examples

Simple LipidsEsters 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

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Classification 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

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Classification 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

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Classification Examples

Substances Associated with

Lipids

•Carotenoids•Tocopherols•Vitamins A, D, E and K•Steroids (Cholesterol)

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

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Chemical Composition of Fats

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ANIMALS AND VEGETABLE FATS

Complex mixtures

of glyceride

s

Esters of glycerol & fatty acids

Triglycerides

(TAG)-Neutral

fats

3 molecules of fatty acids - glycerol

Triglycerides

One molecule of glycerol + 3 molecules

of fatty acids (condensation)

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

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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)

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• 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)

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• 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)

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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

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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) 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

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Essential Fatty Acids (Polyunsaturated Fatty Acids)

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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

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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)

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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

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What are Phospholipids?

• Lipids containing phosphorus

• Are good emulsifying agents

• Found in cell membranes and in subcellular structures (lipid & water interaction)

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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

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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

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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

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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

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CHOLESTEROL

AtherosclerosisPlaque aroundThe artery Hardening &Narrowing

Hyperthyroidism

Diabetes Mellitus

Xanthomatosis(fat storage disorder)

Myxoedema (Hypothyroidism)

Nephrotic syndrome(kidney disorder)

Obstructive jaundice

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

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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.

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Distribution of Lipoproteins: Body tissues

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LIPOPROTEINS

Nucleus, MitochondriaMicrosome

Thromboplastin(prothrombin-

thrombin)

Cell membranes

Rhodopsin(combination ofprotein, opsin and retinal aldehyde of Vit. A

PlasmaCholesterol,Phospholipids, neutral fat, traces of fat soluble vitaminsSteroid hormone

Fat droplets in milkEgg yolk

(HDL & LDL)

Lipoproteins according to Density

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Type Densityg/ml

Protein Triglycerides(TAG)

Cholesterol Phospholipids

Free Ester

Chylomicrons

< 0.95 1 85-95 1-2 1-2 3-6

Very low density lipoproteinVLDL

0.95-1.006

10 50-60 4-8 10 15-20

Low density lipoproteinsLDL

1.006-1.063

22 10 10 38 20

High density lipoproteinsHDL

1.063-1.21

45-60 3 5 15-20 25-30

EVALUATION

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• 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?

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