Lipids
LIPIDS
•
Lipids are a large and diverse group of naturally occurring organic
compounds that are related by their solubility in nonpolar organic solvents
and general insolubility in water.
• They are formed by condensation reaction between fatty acids and
alcohols.
• Lipids are esters of moderate to long chain fatty acids
• The main biological functions of lipids include energy storage, as structural
components of cell membranes, and as important signalling molecules.
• Lipids are non-polar (hydrophobic) compounds, soluble in organic solvents
such as chloroform, methanol.
FATTY ACIDS
• The lipid building blocks.
• Fatty acids consist of a hydrocarbon chain with a
carboxylic acid at one end.
• The fatty acid chains are usually between 10 and 20
Carbon atoms long.
• The fatty "tail" is non-polar (Hydrophobic) while the
Carboxyl "head" is a little polar (Hydrophillic).
• Eg: A 16-C fatty acid: CH3(CH2)14-COONon-polar polar
Fatty Acids
• The carbon chain of fatty acids may be saturated or
unsaturated.
• Where a double bond exists, there is the possibility of
either a cis or a trans geometric isomerism.
• Most naturally occurring fatty acids are of the cis
configuration.
Cis and trans-2-butene
Fatty acids
• Fatty acids are of two types:
• Saturated : only single bonds between Carbon
atoms
• Unsaturated : contain one or more double
bonds.
• The double bond gives unsaturated fatty acids
a bend in the chain. This bend affects the
chemical characteristics of unsaturated fatty
acids.
Saturated FattyAcids
• Contain only single C–C
bonds
• Closely packed
• Strong attractions between
chains
• High melting points
• Solids at room temperature
• Eg: Butter,
6
Unsaturated Fatty Acids
• Contain one or more
double C=C bonds
• Nonlinear chains do not
allow molecules to pack
closely
• Few interactions between
chains
• Low melting points
• Liquids at room
temperature
• Eg: Vegetable oils
7
Examples of Fatty Acids
Most naturally occurring fatty acids have an even number of
carbon atoms.
Some fatty acids and their common names:
14:0 myristic acid
16:0 palmitic acid
Naming a Fatty Acid:
First digit: No of Carbon atoms
18:0 stearic acid
Second Digit: No of double
18:1 cisD9 oleic acid
bonds
9,12
18:2 cisD
linoleic acid
DN : Position of Double bond
18:3 cisD9,12,15 a-linolenic acid
20:4 cisD5,8,11,14 arachidonic acid
Classification of Lipids
• Based on their functions lipids are classified as
• Storage Lipids: Triglycerides
• Membrane Lipids: Phospholipids, Glycolipids
Storage Lipids: Triglycerides
• The triesters of fatty acids with glycerol compose
the class of lipids known as fats and oils.
• These triglycerides are found in both plants and
animals.- they are the simplest lipids
• Triglycerides that are solid or semisolid at room
temperature are classified as fats, and occur
predominantly in animals.
• Those triglycerides that are liquid are called oils
and originate chiefly in plants.
Storage Lipids: Triglycerides
• Triglycerides are Energy-storage molecules.
They are formed by connecting three fatty
acids to a molecule Glycerol.
Storage Lipids :Waxes
• Biological waxes are esters of long-chain (C14 to
C36) saturated and unsaturated fatty acids with
long-chain (C16 to C30) alcohols.
• In addition to being storage form of metabolic
fuel, waxes have other diverse roles: as waterrepellent, coating on leave surface to prevent
excess evaporation
Membrane Lipids: Phospholipids
• This class of lipids are really derivatives of
triglycerides.
• They are composed of a glycerol molecule with
two fatty acids (a diglyceride).
• The third carbon contains a phosphate group and
usually some added polar molecule (such as
ethanolamine, serine or choline)
Membrane Lipids :Phospholipids
• Major
component
of
all cell membranes as
they can form lipid
bilayers.
Membrane Lipids:Glycolipids
• Glycolipids are composed of lipids that are
covalently bonded to monosaccharides or
polysaccharides.
• Their role is to provide energy and also serve
as markers for cellular recognition.
Sphingolipids
• Are a class of lipids which are composed of
one molecule of long chain alcohol called
sphingosine.
• Instead of glycerol these lipids have
Sphingosine.
• These compounds play important
roles in signal transmission and
cell recognition
Membrane Lipids: Cholesterol
Cholesterol, an important constituent of cell membranes, has a rigid ring
system and a short branched hydrocarbon tail.
Cholesterol is largely hydrophobic.
But it has one polar group, a hydroxyl, making it amphipathic.
HO
Cholesterol
SUMMARY