Download Unit 7 Chemistry of Lipids

UNIT 3
CHEMISTRY OF LIPIDS
OBJECTIVES
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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
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
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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 lipoproteins
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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)
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
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Classification of Lipids
LIPIDS
Simple Lipids
Compound Lipids
Derived Lipids
Substances Associated with Lipids
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Classification of Lipids
Classification
Simple Lipids
Definition
Examples
Esters of fatty acids * Neutral fats (F.A. + alcohol)
with various alcohols * Glycerol (alcohol in fats)
* Anything other than glycerol
(alcohol in waxes)
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Classification of Lipids
Classification
Compound
Lipids
•Phospholipids
•Glycolipids
Description
Contains other chemical
groups in addition to alcohol
and fatty acids
4 Sub-Divisions
•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
•Sulpholipids
•Lipoprotein
•Attached to proteins (present in plasma &
tissues)
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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)
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Classification of Lipids
Classification
Examples
•Carotenoids
Substances Associated •Tocopherols
with Lipids
•Vitamins A, D, E and K
•Steroids (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
18
Chemical Composition of Fats
ANIMALS AND VEGETABLE FATS
Complex
mixtures of
glycerides
Esters of glycerol & fatty acids
Triglycerides
Triglycerides
(TAG)Neutral fats
3 molecules of fatty acids - glycerol
One molecule of glycerol + 3 molecules
of fatty acids (condensation)
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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
25
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)
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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
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 bodymust be taken in the diet)
•Linoleic acid – the only fatty
acid which is absolutely
indispensable.
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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
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. LiebermannBurchard reaction) – blue or
green color
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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
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Functions of Cholesterol
Atherosclerosis
Plaque around
The artery
Hardening &
Narrowing
Diabetes Mellitus
Myxoedema
(Hypothyroidism)
CHOLESTEROL
Hyperthyroidism
Xanthomatosis
(fat storage
disorder)
Obstructive jaundice
Nephrotic syndrome
(kidney disorder)
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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
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.
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Distribution of Lipoproteins:
Body tissues
Cell membranes
Nucleus,
Mitochondria
Microsome
Thromboplastin
(prothrombinthrombin)
LIPOPROTEINS
Egg yolk
(HDL & LDL)
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
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Lipoproteins according to Density
Type
Density
g/ml
Protein
Triglycerides
(TAG)
Cholesterol
Free
Ester
Phospholipids
Chylomicrons
< 0.95
1
85-95
1-2
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
1.063-1.21
45-60
3
5
15-20
25-30
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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
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