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Biochemistry METABOLISM OF LIPIDS
Classification of Lipids
Dr. Vijaya Khader Dr. MC Varadaraj
Paper : 05 Metabolism of Lipids
Module: 04 Classification of Lipids
Principal Investigator
Paper Coordinator and
Content Writer
Dr. Sunil Kumar Khare, Professor,
Department of Chemistry, IIT-Delhi
Dr. Suaib Luqman, Scientist (CSIR-CIMAP)
& Assistant Professor (AcSIR)
CSIR-CIMAP, Lucknow
Content Reviewer Prof. Prashant Mishra, Professor,
Department of Biochemical Engineering
and Biotechnology, IIT-Delhi
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Biochemistry METABOLISM OF LIPIDS
Classification of Lipids
DESCRIPTION OF MODULE
Subject Name Biochemistry
Paper Name 05 Metabolism of Lipids
Module Name/Title 04 Lipids-Classification
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Biochemistry METABOLISM OF LIPIDS
Classification of Lipids
1. Objectives
To understand the classification of lipids
How many classes of lipids are present
What are the significance of each class
2. Concept Map
Natural Lipids Phospho Lipids
Glyco Lipids Terpenoids
Conn & Stumpf
(1966)
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Biochemistry METABOLISM OF LIPIDS
Classification of Lipids
3. Description
Lipids can be broadly classified into following major classes: (a) Saponifiable lipids and (b) Non-saponifiable
lipids. This classification is based on the basics of their reaction with sodium or potassium hydroxide.
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Biochemistry METABOLISM OF LIPIDS
Classification of Lipids
a. The saponifiable lipid has one or more ester groups allocating it to endure hydrolysis in the charisma of
an acid, base or enzyme.
b. The non-saponifiable lipid includes phospholipids, prostaglandins, sphingolipids, steroids, terpenes,
triglycerides and waxes which cannot be wrecked up into smaller molecules by hydrolysis.
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Biochemistry METABOLISM OF LIPIDS
Classification of Lipids
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Biochemistry METABOLISM OF LIPIDS
Classification of Lipids
On the basis of polarity, lipids are divided into two classes: (1) Polar and (2) Non-Polar
1. Polar (Glycerophospholipids & Sphingolipids): Some of the characteristic of polar lipids are as under.
a. It forms bilayer impulsively in water. Phosphatidyl choline (PC, a purified polar lipid from
membranes) restrain up to 30 combinations of fatty acids on its chains.
b. The bilayers of lipid have four states: Crystal, Gel, Liquid and Liquid crystal. It exhibits a sharp Tm
defined from the gel to liquid crystal transition. The Tm is very soaring for saturated chains and
very short for polyunsaturated chains.
c. In the liquid crystal state, biological membranes are always just over the Tm. Examples are fish
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Biochemistry METABOLISM OF LIPIDS
Classification of Lipids
and alcoholics.
d. There are three sub-classes of polar lipids: anionic, uncharged and zwitter-ionic. No
cationic lipids are reported in nature.
Anionic Lipids
Examples of the anionic lipids are Cardiolipin (CL), Phosphotidyl glycerol (PG), Phosphotidyl inositol (PI),
Phosphotidyl serine (PS) and many others.
i. Agreement of X-ray structures of crystals with NMR conformations.
ii. Vile interactions improved by screening of cations from solution and H-bonds.
iii. pH at the surface lower that of water (2-3 units if not in salt) and the pH difference wanes off at high
ionic strength.
iv. The anionic lipids constantly involved in fusion and the surface can bind calcium and hydrogen
which eases fusion.
v. Cardiolipin acts as an acid-anion provokes hydrogen ion to operate as an attractant. Fusion arises
because of acid-anion formation and negative charges become striking by trapping protons.
vi. The entire membranes have a net negative charge on their exterior that attracts cations (H+ & Na
++).
vii. Similarly, all biological membranes have a proton gradient sustained by a proton pump (except
presence of sodium gradient in animal plasma membrane).
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Biochemistry METABOLISM OF LIPIDS
Classification of Lipids
Uncharged Lipids
Examples of the uncharged lipids are Cerebrosides, Gangliosides and Glycolipids. The surface of
gangliosides & sphingolipids are anionic but have H-bond lateral interactions. Glycolipids have H-bonds
amid neighbours with each lipid has three neighbours.
Zwitter-Ionic Lipids
Examples of the zwitter-ionic lipids are Phosphotidyl choline (PC), Phosphatidyl ethanolamine (PE),
Sphingomyelin (SM).
i. Position wise phosphate is on top of the glycerol and glycerol is upright to the membrane.
ii. Primary ester is underneath the glycerol and secondary ester is parallel to the membrane
before (at C2) the chain plunges.
iii. Choline/Ethanolamine (base) gyrates at an angle of ~15º to the plane.
iv. Each headgroup of zwitter ionic lipids interact with three neighbours ionically (+,-)
2. Non-polar (Triglycerides)
A lot of lipids, on the other hand, are non-polar, implicating that the charge allocation is uniformly
distributed. Infact, non-polar molecules do not dissolve well in water. Polar and non-polar molecules
tend to deter each other in the similar way as the oil and water do not mix and will split from each other
even if they are shaken robustly in an endeavor to mix them. This peculiarity between non-polar and
polar molecules has imperative effect for living things, which are poised of both molecules.
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Biochemistry METABOLISM OF LIPIDS
Classification of Lipids
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Biochemistry METABOLISM OF LIPIDS
Classification of Lipids
On the basis of function, lipids can be classified into following:
1. Storage lipids (Fatty acids, Triacylglycerols, Sterols)
2. Structural lipids in membranes (Phospholipids, Saccharolipids)
3. Lipids as signals, cofactors and pigments (Lipoproteins, Proteolipids, Polyketides)
In the beginning it was understood that lipids are oily substance utilized for two major reasons: (a) dole out as
energy souce and (b) structural blocks of membranes. George & Mildred Burr (1929) on the other hand drive out
this allegory and established linoleic acid as an indispensable dietary constituent that play an imperative function
in many processes in the body. Bergström et al., (1964) also revealed arachidonate (EFA) as the antecedent of
the prostaglandins and explained its effect on inflammation and allied disease giving impetus to lipids that
gained new-fangled significance among biochemists.
Amphipathic nature of membrane lipids and orientation of their hydrophilic and hydrophobic regions articulate
their stuffing into the bilayer. Among structural membrane lipids, three types have been described: (a)
Glycerophospholipids (two fatty acids connected to glycerol are present in hydrophobic regions), (b)
Sphingolipids (sphingosine: a fatty amine linked to single fatty acid) and (c) sterols (compounds with four fused
hydrocarbon rings arranged in an inflexible arrangement). Glycerophospholipids and sphingolipids include
charged alcohols at their polar ends and a few in addition contain phosphate moeity. In these amphipathic
compounds, the hydrophilic moieties could be more complex or as elementary as a single -OH group at one end
of the sterol ring system. Among these membrane lipids classes, colossal miscellany results from various
combinations of ‘tails’ and polar ‘heads’ of fatty acid.
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Biochemistry METABOLISM OF LIPIDS
Classification of Lipids
The products of hydrolysis have also been considered for classifying the lipids into following category.
1. Simple Lipids: On hydrolysis yield alcohol (monohydric or trihydric) and fatty acids
Simple glyceride: Include identical FAs
Mixed glyceride: Include dissimilar FAs
Oils: Glycerol with UFAs
Fats: Glycerol with SFAs
Waxes: Mono or dihydric alcohol with FAs
2. Complex Lipids: (Compound lipids): On hydrolysis yield fatty acids, glycerol and phosphoric acid along
with serine, sphingosine, ethanolamine and various sugars.
Phospholipid: Glycerol + fatty acids + phosphoric acid + nitrogenous base
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Biochemistry METABOLISM OF LIPIDS
Classification of Lipids
e.g. Lecithin: Glycerol + fatty acids + phosphoric acid + choline
Cephalin: Glycerol + fatty acids + phosphoric acid + ethanolamine
Glycolipids: Glycerol + fatty acid + carbohydrates (on hydrolysis)
They are sub-classified as sulpholipids, galactosyl diglyceride and cerebrosides.
Sphingophosphoiplds: Sphingosine + fatty acids + phosphoric acid + choline
3. Derived Lipids: Are the hydrolytic commodities of complex and simple lipids.
Examples are Alcohols (Sterol and glycerol), fatty acids, terpenoids etc.
4. Summary
In this lecture we learnt about:
The Different types of classifications of the lipids