Lipids are biomolecules that are not soluble in water but soluble in organic solvents. They are formed through condensation reactions between fatty acids and alcohols. The main types of lipids include fatty acids, triglycerides, phospholipids, waxes, fats and oils, and steroids. Lipids serve important structural and energy storage functions in organisms. They are the main components of biological membranes and are stored as triglycerides in adipose tissue to be used as an energy source when needed.

1.  ‘‘liposlipos’’ –– fatsfats
 biomoleculebiomolecule which is not soluble in aqueous solutionswhich is not soluble in aqueous solutions
but soluble in organic solventsbut soluble in organic solvents
 formed by condensation reactions between fatty acidsformed by condensation reactions between fatty acids
& alcohol.& alcohol.
 Most lipid are triglyceridesMost lipid are triglycerides
 do not have distinct chemical or structuraldo not have distinct chemical or structural
characteristicscharacteristics
 Types of lipids:Types of lipids:
Fatty acidsFatty acids
TriglycerolsTriglycerols
PhospholipidsPhospholipids
Waxes, fats, oilsWaxes, fats, oils
SteroidsSteroids
LIPIDSLIPIDS

2. Classification of lipidsClassification of lipids

3. Functions of Lipids:Functions of Lipids:
 Structural components of biological membranesStructural components of biological membranes
(lipoprotein, phospholipids &(lipoprotein, phospholipids & sphingolipidssphingolipids))
 Several proteins are covalently modified by fattySeveral proteins are covalently modified by fatty
acidsacids
 energy/food reservoir (energy/food reservoir (triglycerolstriglycerols))
 Fatty acid derivatives serve as vitamins orFatty acid derivatives serve as vitamins or
hormoneshormones
 Fat is stored in adipose tissue, where it also servesFat is stored in adipose tissue, where it also serves
as a thermal insulator in the subcutaneous tissuesas a thermal insulator in the subcutaneous tissues
and around certain organsand around certain organs

4.  Simple LipidSimple Lipid:: Esters of fatty acids withEsters of fatty acids with
various alcohols.various alcohols.
a.a. Fats:Fats: Esters of fatty acids with glycerol.Esters of fatty acids with glycerol.
OilsOils are fats in the liquid state.are fats in the liquid state.
b.b. Waxes:Waxes: Esters of fatty acids with higherEsters of fatty acids with higher
molecular weight monohydric alcohols.molecular weight monohydric alcohols.

5.  Complex lipidsComplex lipids:: Esters of fatty acidsEsters of fatty acids
containing groups in addition to ancontaining groups in addition to an
alcohol and a fatty acid.alcohol and a fatty acid.
a.a. Phospholipids:Phospholipids: Lipids containing, inLipids containing, in
addition to fatty acids and an alcohol, aaddition to fatty acids and an alcohol, a
phosphoric acid residue.phosphoric acid residue.
b.b. GlucolipidsGlucolipids:: Lipids containing a fattyLipids containing a fatty
acid, an alcohol, and carbohydrate.acid, an alcohol, and carbohydrate.

6. A. Fatty acids…A. Fatty acids…
 Fatty acids are aliphatic carboxylic acidFatty acids are aliphatic carboxylic acid
 long straight chains of hydrocarbon present ending withlong straight chains of hydrocarbon present ending with
––COOH groupCOOH group (10(10--24 C)24 C)
 GeneralGeneral Formula: RFormula: R--COOH, RCOOH, R = H,= H, --CHCH33,, --CC22HH55, etc…, etc…
 The chain may be saturated (containing no doubleThe chain may be saturated (containing no double
bonds) or unsaturated (containing one or more doublebonds) or unsaturated (containing one or more double
bonds).bonds).

7.  Fatty acids occur mainly as esters in naturalFatty acids occur mainly as esters in natural
fats and oilsfats and oils
 Fatty acid chain is saturated inFatty acid chain is saturated in FatsFats, while, while
unsaturated inunsaturated in OilsOils..
 different from each other by:different from each other by:
 length of hydrocarbonlength of hydrocarbon
 degree of saturationdegree of saturation
 position of double bond in chainposition of double bond in chain

8. Saturated or unsaturated??Saturated or unsaturated??
 SaturatedSaturated ––
without doublewithout double
bond;bond;
e.g.:e.g.:
palmiticpalmitic acid (16:0),acid (16:0),
stearicstearic acid (18:0),acid (18:0),
myristicmyristic acid (14:0)acid (14:0)
 UnsaturatedUnsaturated –– with onewith one
or more double bond;or more double bond;
 e.g.:e.g.:
palmitoleicpalmitoleic acid (16:1),acid (16:1),
oleic acid (18:1),oleic acid (18:1),
linoleiclinoleic acid (18:2)acid (18:2)
 types of unsaturatedtypes of unsaturated
fatty acids: monofatty acids: mono--,, didi--,,
tritri--,, polipoli--

9. ~ Melting point of fatty acids:~ Melting point of fatty acids:
-- saturatedsaturated -- high; solid formhigh; solid form
-- unsaturatedunsaturated -- low; liquid formlow; liquid form

10.  Orientation of unsaturated fattyOrientation of unsaturated fatty
acids:acids:
Naturally occurring unsaturated long-chain fatty acids are nearly all of the
cis configuration, the molecules being “bent” 120 degrees

11. ‘kink’/’bend’
NomenclatureNomenclature
 Named according to the number of carbon atoms in theNamed according to the number of carbon atoms in the
chain & position of any double bondschain & position of any double bonds

12. With increase in C melting point increases, with increase in unsaturation melting
point decreases

13.  Essential fatty acidsEssential fatty acids (EFA): body require them(EFA): body require them
but cannot synthesize i.e.but cannot synthesize i.e. --3,3, --6,6, --99
Gives energy as
well as helps in
biological
processes.
Found in fish oil,
egg oil, squid oil,
Nuts, flaxseed etc.
EFA comes under
category of PUFA.
Only two EFAs
are known for
humans: alpha-
linolenic
acid (an omega-3
fatty acid)
and linoleic
acid (an omega-6
fatty acid)

14. B.B. TriacylglycerolTriacylglycerol/triglyceride/triglyceride
 It is a simple lipid classified as fats or oils.It is a simple lipid classified as fats or oils.
 They are main storage form of fatty acid.They are main storage form of fatty acid.
 Commonest form of lipidCommonest form of lipid
 Made up of 3 fatty acids & 1 glycerolMade up of 3 fatty acids & 1 glycerol
moleculesmolecules –– ester bond through condensationester bond through condensation
processprocess
 hydrophobic; animal energy reservoirhydrophobic; animal energy reservoir
 each one differs in terms of identity & positioneach one differs in terms of identity & position
of fatty acids residuesof fatty acids residues
 solid form (fats) or liquid form (oils)solid form (fats) or liquid form (oils)
 fatsfats –– produce more energy per mass unitproduce more energy per mass unit
compared to carbohydrate/proteincompared to carbohydrate/protein

15. GG
LL
YY
CC
EE
RR
OO
LL
FF
AA
TT
TT
YY
AA
CC
II
DD
SS
1
2
3

16.  adipose tissueadipose tissue –– cells containing fats & oils; found oncells containing fats & oils; found on
subcutaneous layer, abdominal space, around mainsubcutaneous layer, abdominal space, around main
organs; energy storage; insulator; protectionorgans; energy storage; insulator; protection
 adipocytesadipocytes/fatty cells/fatty cells –– triacylglyceroltriacylglycerol synthesis &synthesis &
storage; consist of fatty globulesstorage; consist of fatty globules
 hydrolyzed by lipaseshydrolyzed by lipases
 In practice, naturalIn practice, natural acylglycerolsacylglycerols
contain a mixture of fatty acids tailoredcontain a mixture of fatty acids tailored
to suit their functional roles.to suit their functional roles.
Lipids in adipose
tissues

17. C.C. PhospholipidPhospholipid//phosphoglyceridephosphoglyceride
 lipid with phosphate head grouplipid with phosphate head group
 main membrane component, emulsifying agent & surfacemain membrane component, emulsifying agent & surface
active agent.active agent.
 consists of glycerolconsists of glycerol--33--phosphate wherebyphosphate whereby
its C1 & C2its C1 & C2 esterifiedesterified with fatty acids &with fatty acids &
phosphorylphosphoryl grpgrp linked to Xlinked to X grpgrp withwith phosphodiesterphosphodiester bondbond
XX grpgrp:: They frequently have nitrogen containing basesThey frequently have nitrogen containing bases
and otherand other substituentssubstituents..
 ampiphilicampiphilic molecules with nonmolecules with non--polar aliphatic end & polarpolar aliphatic end & polar
phosphorylphosphoryl--X headX head grpgrp..
 e.g.:e.g.: phosphatidicphosphatidic acid,acid, phosphatidylphosphatidyl ethanolamine;ethanolamine;
phosphatidylphosphatidyl colinecoline;; phosphatidylphosphatidyl serine;serine; phosphatidylphosphatidyl
inositolinositol

18. X Group

19. D. Wax…D. Wax…
 nonpolar ester of long chain fattynonpolar ester of long chain fatty
acid & long chain monohydroxylicacid & long chain monohydroxylic
alcoholalcohol
 one weak hydrophilic head bondedone weak hydrophilic head bonded
to 2 hydrocarbon chainsto 2 hydrocarbon chains
 water insolublewater insoluble
 functionsfunctions –– energy storage;energy storage;
structural componentstructural component
 thickness increase with chain lengththickness increase with chain length
& hydrocarbon saturation degree& hydrocarbon saturation degree