unit 3 chemistry of lipids. objectives define lipids and its occurrence state the biological...
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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