Download Lipids lecture(1) by Prof.Dr.Moaed Al

2016
Lipids lecture(1) by Prof.Dr.Moaed Al-Gazally
Chemistry of Lipids
Lipids constitute a heterogeneous group of compounds of
biochemical importance. Lipids may be defined as compounds which
are relatively insoluble in water, but freely soluble in nonpolar
organic solvents like benzene, chloroform, ether, hot alcohol, acetone,
etc.
Functions of Lipids
1. Storage form of energy (triglycerides).
2.Structural
components
of
biomembranes
(phospholipids
and
cholesterol).
3. Metabolic regulators (steroid hormones and prostaglandins).
4. Act as surfactants, detergents and emulsifying agents (amphipathic
lipids).
2016
Lipids lecture(1) by Prof.Dr.Moaed Al-Gazally
5. Act as electric insulators in neurons.
6.Provide
insulation
against
changes
in
external
temperature
(subcutaneous fat)
7. Give shape and contour to the body.
8. Protect internal organs by providing a cushioning effect (pads of fat)
9. Help in absorption of fat soluble vitamins (A, D, E and K)
10. Improve taste and palatability of food.
Clinical Applications
1. Excessive fat deposits cause obesity. Truncal obesity is a risk factor for
heart attack.
2.Abnormality in cholesterol and lipoprotein metabolism leads to
atherosclerosis and cardiovascular diseases .
3. In diabetes mellitus, the metabolisms of fatty acids and lipoproteins are
deranged, leading to ketosis.
Calcification of lipids
Based on the chemical nature, lipids are classified as:
1.Simple lipids: They are esters of fatty acids with glycerol or other
higher alcohols .
a. Triacylglycerol or Triglycerides or neutral fat
b. Waxes
2016
Lipids lecture(1) by Prof.Dr.Moaed Al-Gazally
2. Compound lipids : They are fatty acids esterified with alcohol; but
in addition they contain other groups. Depending on these extra groups,
they are subclassified in to
A) Phospholipids, containing phosphoric acid:
1. Nitrogen containing glycerophosphatides:
i. Lecithin (phosphatidyl choline)
ii. Cephalin (phosphatidyl ethanolamine)
iii. Phosphatidyl serine
2. Non-nitrogen glycerophosphatides
i. Phosphatidyl inositol
ii. Phosphatidyl glycerol
iii. Diphosphatidyl glycerol (cardiolipin)
3. Plasmalogens, having long chain alcohol
i. Choline plasmalogen
ii. Ethanolamine plasmalogen
4. Phospho sphingosides, with sphingosine
Sphingomyelin.
B) Non-phosphorylated lipids
1. Glycosphingolipids (carbohydrate)
i. Cerebrosides (ceramide monohexosides)
oligosaccharides)
ii. Globosides (ceramide
iii. Gangliosides (ceramide + oligosaccharides
+ N-acetyl neuraminic acid)
2. Sulpholipids or sulfatides
i. Sulphated cerebrosides
ii. Sulphated globosides
iii. Sulphated gangliosides
3. Derived lipids: They are compounds which are derived from lipids
or precursors of lipids, e.g. fatty acids, steroids. Proteolipids and
lipoproteins.
4. Lipids complexes to other compounds: Proteolipids and
lipoproteins.
2016
Lipids lecture(1) by Prof.Dr.Moaed Al-Gazally
Fatty acids
Fatty acids, are included in the group of derived lipids. It is the most
common component of lipids in the body. They are generally found in
ester linkage in different classes of lipids. In the human body free fatty
acids are formed only during metabolism. Fatty acids are aliphatic
carboxylic acids and have the general formula, R—CO—OH, where
COOH (carboxylic group) represents
the functional
group.
Depending on the R group (the hydrocarbon chain), the physical
properties of fatty acids may vary.
Classification of fatty acids
1. Depending on total number of carbon atoms:
a. Even chain :They have carbon atoms 2,4,6 and similar series.
Most of the naturally occurring lipids contain even chain fatty acids.
b. Odd chain :They have carbon atoms 3, 5, 7, etc. Odd numbered fatty
acids are seen in microbial cell walls. They are also present in milk.
2. Depending on length of hydrocarbon chain:
a. Short chain with 2 to 6 carbon atoms.
b.Medium chain with 8 to 14 carbon atoms.(Capric acid 10 C)
c. Long chain with 16 to 22 carbon atoms.(Linoleic acid 16 C).
2016
Lipids lecture(1) by Prof.Dr.Moaed Al-Gazally
d. Very long chain fatty acids (more than 24 carbon)
3. Depending on nature of hydrocarbon chain:
a. Saturated fatty acids .
b. Unsaturated fatty acids which may be sub classified into Monounsaturated (mono-enoic) having single double bond or Polyunsaturated
(poly-enoic) with 2 or more double bonds .
c. Branched chain fatty acids
d. Hydroxy fatty acids.
Saturated fatty acids
Franz Soxhlet, a German chemist, invented the Soxhlet apparatus in
1879.
i. They have the general formula CH3-(CH2)n- COOH. For example,
Acetic acid CH3—COOH
Butyric acid CH3(CH2)2—COOH
Palmitic acid CH3—(CH2)14—COOH
Stearic acid CH3—(CH2)16—COOH
2016
Lipids lecture(1) by Prof.Dr.Moaed Al-Gazally
ii. They are named by adding the suffix ‘anoic' after the hydrocarbon.
iii. The two carbon acetic acid and 4 carbon butyric acid are important
metabolic intermediates.
iv. The C16 (palmitic acid) and C18 (stearic acid) are most abundant in
body fat.
v. Each animal species will have characteristic pattern of fatty acid
composition. Thus human body fat contains 50% oleic acid, 25%
palmitic acid 10% linoleic and 5% stearic acid.
vi. The carbon atoms of fatty acids are numbered as C1, C2, etc (Delta
system) starting from the COOH group. Or, starting from the methyl end,
the carbon atoms may be numbered as omega system (ω)-1,2,3,etc.
6
5
4
3
2
1
CH3 — CH2 — CH2 — CH2— CH2 — COOH
ω1
ω2
ω3
ω4
ω5