‘‘liposlipos’ ’ –– fatsfats biomoleculebiomolecule which is not soluble in aqueous solutions which is not soluble in aqueous solutions

but soluble in organic solventsbut soluble in organic solvents formed by condensation reactions between fatty acids formed by condensation reactions between fatty acids

& alcohol.& alcohol. Most lipid are triglyceridesMost lipid are triglycerides do not have distinct chemical or structural do not have distinct chemical or structural

characteristicscharacteristics Types of lipids:Types of lipids:

Fatty acidsFatty acidsTriglycerolsTriglycerolsPhospholipids Phospholipids Waxes, fats, oilsWaxes, fats, oilsSteroidsSteroids

LIPIDSLIPIDS

Classification of lipidsClassification of lipids

Functions of Lipids:Functions of Lipids: Structural components of biological membranes Structural components of biological membranes

(lipoprotein, phospholipids & (lipoprotein, phospholipids & sphingolipidssphingolipids)) Several proteins are covalently modified by fatty Several proteins are covalently modified by fatty

acidsacids energy/food reservoir (energy/food reservoir (triglycerolstriglycerols)) Fatty acid derivatives serve as vitamins or Fatty acid derivatives serve as vitamins or

hormoneshormones Fat is stored in adipose tissue, where it also serves Fat is stored in adipose tissue, where it also serves

as a thermal insulator in the subcutaneous tissues as a thermal insulator in the subcutaneous tissues and around certain organsand around certain organs

Simple LipidSimple Lipid: : Esters of fatty acids with Esters of fatty acids with various alcohols.various alcohols.

a.a. Fats: Fats: Esters of fatty acids with glycerol. Esters of fatty acids with glycerol. Oils Oils are fats in the liquid state.are fats in the liquid state.

b.b. Waxes: Waxes: Esters of fatty acids with higher Esters of fatty acids with higher molecular weight monohydric alcohols.molecular weight monohydric alcohols.

Complex lipidsComplex lipids:: Esters of fatty acids Esters of fatty acids containing groups in addition to an containing groups in addition to an alcohol and a fatty acid.alcohol and a fatty acid.

a.a. Phospholipids:Phospholipids: Lipids containing, in Lipids containing, in addition to fatty acids and an alcohol, a addition to fatty acids and an alcohol, a phosphoric acid residue. phosphoric acid residue.

b.b. GlucolipidsGlucolipids:: Lipids containing a fatty Lipids containing a fatty acid, an alcohol, and carbohydrate.acid, an alcohol, and carbohydrate.

A. Fatty acids…A. Fatty acids… Fatty acids are aliphatic carboxylic acidFatty acids are aliphatic carboxylic acid long straight chains of hydrocarbon present ending with long straight chains of hydrocarbon present ending with

––COOH group COOH group (10(10--24 C)24 C) General General Formula: RFormula: R--COOH, R COOH, R = H, = H, --CHCH33, , --CC22HH55, etc…, etc… The chain may be saturated (containing no double The chain may be saturated (containing no double

bonds) or unsaturated (containing one or more double bonds) or unsaturated (containing one or more double bonds).bonds).

Fatty acids occur mainly as esters in natural Fatty acids occur mainly as esters in natural fats and oilsfats and oils

Fatty acid chain is saturated in Fatty acid chain is saturated in FatsFats, while , while unsaturated in unsaturated in OilsOils..

different from each other by:different from each other by: length of hydrocarbon length of hydrocarbon degree of saturationdegree of saturation position of double bond in chainposition of double bond in chain

Saturated or unsaturated??Saturated or unsaturated??

Saturated Saturated ––without double without 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)

Unsaturated Unsaturated –– with one with 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 unsaturated types of unsaturated fatty acids: monofatty acids: mono--, , didi--, , tritri--, , polipoli--

~ Melting point of fatty acids:~ Melting point of fatty acids:

-- saturated saturated -- high; solid formhigh; solid form-- unsaturated unsaturated -- low; liquid formlow; liquid form

Orientation of unsaturated fatty Orientation 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

‘kink’/’bend’

NomenclatureNomenclature Named according to the number of carbon atoms in the Named according to the number of carbon atoms in the

chain & position of any double bondschain & position of any double bonds

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

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)

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 glycerol Made up of 3 fatty acids & 1 glycerol

molecules molecules –– ester bond through condensation ester bond through condensation processprocess

hydrophobic; animal energy reservoirhydrophobic; animal energy reservoir each one differs in terms of identity & position each 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) fats fats –– produce more energy per mass unit produce more energy per mass unit

compared to carbohydrate/proteincompared to carbohydrate/protein

GG

LL

YY

CC

EE

RR

OO

LL

FF

AA

TT

TT

YY

AA

CC

II

DD

SS

1

2

3

adipose tissue adipose tissue –– cells containing fats & oils; found on cells containing fats & oils; found on subcutaneous layer, abdominal space, around main subcutaneous 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, natural In practice, natural acylglycerolsacylglycerolscontain a mixture of fatty acids tailored contain a mixture of fatty acids tailored to suit their functional roles. to suit their functional roles.

Lipids in adipose tissues

C. C. PhospholipidPhospholipid//phosphoglyceridephosphoglyceride

lipid with phosphate head grouplipid with phosphate head group main membrane component, emulsifying agent & surface main membrane component, emulsifying agent & surface

active agent.active agent. consists of glycerolconsists of glycerol--33--phosphate wherebyphosphate whereby

its C1 & C2 its C1 & C2 esterifiedesterified with fatty acids &with fatty acids &phosphorylphosphoryl grpgrp linked to X linked to X grpgrp with with phosphodiesterphosphodiester bondbondX X grpgrp: : They frequently have nitrogen containing bases They frequently have nitrogen containing bases and other and other substituentssubstituents..

ampiphilicampiphilic molecules with nonmolecules with non--polar aliphatic end & polar polar aliphatic end & polar phosphorylphosphoryl--X head X head grpgrp..

e.g.: e.g.: phosphatidicphosphatidic acid, acid, phosphatidylphosphatidyl ethanolamine; ethanolamine; phosphatidylphosphatidyl colinecoline; ; phosphatidylphosphatidyl serine; serine; phosphatidylphosphatidylinositolinositol

X Group

D. Wax…D. Wax…

nonpolar ester of long chain fatty nonpolar ester of long chain fatty acid & long chain monohydroxylic acid & long chain monohydroxylic alcoholalcohol

one weak hydrophilic head bonded one weak hydrophilic head bonded to 2 hydrocarbon chainsto 2 hydrocarbon chains

water insolublewater insoluble

functions functions –– energy storage; energy storage; structural componentstructural component

thickness increase with chain length thickness increase with chain length & hydrocarbon saturation degree& hydrocarbon saturation degree