ByBy

Dr. Dr. M.HassanM.Hassan

LIPIDSLIPIDS

IntroductionIntroduction

Derived from a greek word lipos [fat]Derived from a greek word lipos [fat]They are the substance of biomedical They are the substance of biomedical

importanceimportanceThey are soluble in organic solvents such as They are soluble in organic solvents such as

chloroform and methanol and are chloroform and methanol and are sparingly soluble in H2Osparingly soluble in H2O

Chemically they are esters of different Chemically they are esters of different

alcohols.alcohols.Inaddition to alcohols and fatty acids , some Inaddition to alcohols and fatty acids , some

of the lipids may contain phosphoric acid , of the lipids may contain phosphoric acid , nitrogenous base and carbohydratesnitrogenous base and carbohydrates

CharacteristicsCharacteristics

They are insoluble in H2OThey are insoluble in H2O They are soluble in organic solventThey are soluble in organic solvent Chemically they are esters glycerols Chemically they are esters glycerols

with higher fatty acidwith higher fatty acid

CLASSIFICATION [According to CLASSIFICATION [According to Bloor]Bloor]

A SIMPLE LipidsA SIMPLE Lipids These are the esters of fatty acids These are the esters of fatty acids

with various alcoholswith various alcohols These consist of following subgroupsThese consist of following subgroups

1.Fats [Neutral fats or 1.Fats [Neutral fats or Triacylglycerol]Triacylglycerol]

These are the esters of fatty acids These are the esters of fatty acids with glycerolwith glycerol

The term triacyl glycerol is being The term triacyl glycerol is being used now days rather than used now days rather than triglyceridestriglycerides

2.Waxes2.Waxes

These are the esters of fatty acids These are the esters of fatty acids with alcohol of higher molecular with alcohol of higher molecular weight other than glycerol.These weight other than glycerol.These alcohols are monohydricalcohols are monohydric

B.Compound LipidsB.Compound Lipids

These are the esters of fatty acids These are the esters of fatty acids containing group in addition alcohol containing group in addition alcohol and fatty acidand fatty acid

These are subdivided as followsThese are subdivided as follows

1.Glycolipids [glyco sphingolipids]1.Glycolipids [glyco sphingolipids]

These contain sphingosine , fatty acid These contain sphingosine , fatty acid and a monosaccharide or and a monosaccharide or oligosaccharide unit.oligosaccharide unit.

They contain special alcohol sphingol or They contain special alcohol sphingol or sphingosine , a nitrogenous base in sphingosine , a nitrogenous base in addition to fatty acids.addition to fatty acids.

They does not contain phosphoric acidThey does not contain phosphoric acid They are of two typesThey are of two types A.cerebrosidesA.cerebrosides B.gangliosidesB.gangliosides

2.Sulfo lipids2.Sulfo lipids

Lipids containing sulphate groupLipids containing sulphate group

3.Aminolipids3.Aminolipids

They are also called as proteolipidsThey are also called as proteolipids They are attached with protein They are attached with protein

moleculemolecule In them the parent molecule is lipidIn them the parent molecule is lipid

4.Lipoproteins4.Lipoproteins

In them lipids are the prosthetic In them lipids are the prosthetic group in proteingroup in protein

The parrent is proteinThe parrent is protein

5.Phospholipids5.Phospholipids

These are lipids that contain a These are lipids that contain a phosphoric acid , fatty acid and phosphoric acid , fatty acid and alcoholalcohol

On the basis of type of alcohol On the basis of type of alcohol phospholipids are of two typesphospholipids are of two types

1.If alcohol is 1.If alcohol is glycerol>>>Glycerophospholipidglycerol>>>Glycerophospholipid

2.If alcohol is 2.If alcohol is sphingosin>>>sphingophospholipidsphingosin>>>sphingophospholipid

C..DERIVED LIPIDSC..DERIVED LIPIDS These are obtained by the hydrolysis of simple These are obtained by the hydrolysis of simple

and compound lipidsand compound lipids These areThese are A.[fatty acids]:may be saturated or unsaturated A.[fatty acids]:may be saturated or unsaturated

or cyclicor cyclic B.[monoglycerides]:B.[monoglycerides]: C:DiglycerideC:Diglyceride D:[Alcohols] straight chain alcohols obtained on D:[Alcohols] straight chain alcohols obtained on

hydrolysis of waxeshydrolysis of waxes Cholesterol and other steroids including vitamin DCholesterol and other steroids including vitamin D Vitamin AVitamin A CarotenoidsCarotenoids GlycerolGlycerol

D.MiscellaneousD.Miscellaneous

Vitamin E and Vitamin KVitamin E and Vitamin K CarotenoidsCarotenoids Aliphatic hydrocarbon in liver fat and Aliphatic hydrocarbon in liver fat and

certain hydrocarbon in liver fat and certain hydrocarbon in liver fat and certain hydrocarbons found in bees certain hydrocarbons found in bees wax and plant waxwax and plant wax

Fatty AcidsFatty Acids INTRODUCTIONINTRODUCTION Fatty acids are carboxylic acids with long chain Fatty acids are carboxylic acids with long chain

hydrocarbons side groupshydrocarbons side groups They occur rarely freely in nature , but rather occur in They occur rarely freely in nature , but rather occur in

estrified form as a major components of various lipidsestrified form as a major components of various lipids In higher plants and animals , predominant fatty acid In higher plants and animals , predominant fatty acid

residues those of the C16 and C18 species palmitic , oleic , residues those of the C16 and C18 species palmitic , oleic , linoleic and steric acidslinoleic and steric acids

Fatty acids with 14 and 20 carbon atoms are uncommonFatty acids with 14 and 20 carbon atoms are uncommon Most fatty acids are even number of carbon atom because Most fatty acids are even number of carbon atom because

usually they are biosynthesized by catenation of C2 unitsusually they are biosynthesized by catenation of C2 units Over half of the residues [fatty acids] of plants and animals Over half of the residues [fatty acids] of plants and animals

lipids are unsaturated and often polyunsaturatedlipids are unsaturated and often polyunsaturated Some important fatty acids are discussed belowSome important fatty acids are discussed below

1.Saturated Fatty Acids1.Saturated Fatty Acids They have no double bond in their hydrocarbon They have no double bond in their hydrocarbon

chainchain Symbol of saturated fattyacids have two numbersSymbol of saturated fattyacids have two numbers 1 represent the # of carbon atoms1 represent the # of carbon atoms 2 represent number of double bonds with oxygen2 represent number of double bonds with oxygen Fatty acids with greater than 10 carbon atoms Fatty acids with greater than 10 carbon atoms

are given a systematic names e,g palmitic are given a systematic names e,g palmitic acid ,oleic acid etc.acid ,oleic acid etc.

Palmitic and stearic acids are the two most Palmitic and stearic acids are the two most abundant fatty acids in human beingabundant fatty acids in human being

Lignoceric is component of cerebrosidesLignoceric is component of cerebrosides

2.Unsaturated Fatty Acids2.Unsaturated Fatty Acids They posses one or more double bonds in their They posses one or more double bonds in their

hydrocarbon chainhydrocarbon chain They are more reactive than saturated fatty They are more reactive than saturated fatty

acidacid Fatty acid containing one double bond is called Fatty acid containing one double bond is called

as monoenoic/monounsaturated>>oleic and as monoenoic/monounsaturated>>oleic and palmitoteic acidpalmitoteic acid

Fatty acids containing more than one double Fatty acids containing more than one double bond called as polyenoic/polyunsaturatedbond called as polyenoic/polyunsaturated

>2 double bond dienoic>2 double bond dienoic >3 double bond trienoic>3 double bond trienoic

Physical Properties Of Fatty AcidsPhysical Properties Of Fatty Acids

1.Melting Point1.Melting Point A. Saturated Fatty AcidsA. Saturated Fatty Acids The melting point of saturated The melting point of saturated

F.acids increase with the increase in F.acids increase with the increase in chain lengthchain length

Melting Point Of Unsaturated Fatty Melting Point Of Unsaturated Fatty AcidsAcids

It decrease with increase in unsaturationIt decrease with increase in unsaturation Because fatty acid double bond almost have cis Because fatty acid double bond almost have cis

configuration.This put a rigid 30 degree bend in the configuration.This put a rigid 30 degree bend in the hydrocarbon chain of unsaturated fatty acids that hydrocarbon chain of unsaturated fatty acids that interferes with their efficient packing to fill spaceinterferes with their efficient packing to fill space

E,g oleic acid---14 degree centigrade[1 double bond]E,g oleic acid---14 degree centigrade[1 double bond] Linoleic acid----5 degree centigrade[2 double bonds]Linoleic acid----5 degree centigrade[2 double bonds] Linolenic acid--- -10 degree centigrades[3 double Linolenic acid--- -10 degree centigrades[3 double

bonds]bonds] Vegetable oils---room temp—liquid---unsaturatedVegetable oils---room temp—liquid---unsaturated

2.On hydrogenation under pressure and in the 2.On hydrogenation under pressure and in the presence of Ni catalyst these oils are soldifiedpresence of Ni catalyst these oils are soldified

2.Solubility Of Fatty acids2.Solubility Of Fatty acids 1.Anionic group provides hydrophillic property to the fatty 1.Anionic group provides hydrophillic property to the fatty

acids making them H2O soluble.acids making them H2O soluble. 2. At physiological pH carboxyl group (COOH) ionizes 2. At physiological pH carboxyl group (COOH) ionizes

becoming COO-.becoming COO-. 3.Hydrocarbon chain being hydrophobic tend to make fatty 3.Hydrocarbon chain being hydrophobic tend to make fatty

acid hydrophobic.acid hydrophobic. 4.Chain length of hydrocarbons determine the solubility of 4.Chain length of hydrocarbons determine the solubility of

fatty acids into H2O.fatty acids into H2O. 5.As the chain length increass it decreases the solubility of 5.As the chain length increass it decreases the solubility of

fatty acids into H2O.fatty acids into H2O. 6.E.g CH3COOH has only one methyl group i.e it has short 6.E.g CH3COOH has only one methyl group i.e it has short

hydrocarbon chain length so, it is completely miscible with hydrocarbon chain length so, it is completely miscible with H2O.H2O.

7.Unsaturation also increases the solubility.7.Unsaturation also increases the solubility. 8.E.g palmitoleic acid more soluble than palmitic acid.8.E.g palmitoleic acid more soluble than palmitic acid.

Isomerism in Fatty AcidsIsomerism in Fatty Acids (a). Saturated Fatty Acids.They does not show (a). Saturated Fatty Acids.They does not show

isomerism. They may be straight chain or isomerism. They may be straight chain or branched.branched.

(b).Unsaturated Fatty Acids.Due to the presence of (b).Unsaturated Fatty Acids.Due to the presence of double bond they show isomerism.(i.e cis and trans double bond they show isomerism.(i.e cis and trans configuration)configuration)

1.All naturally occuring unsaturated fatty acids of 1.All naturally occuring unsaturated fatty acids of mammals are of cis configuration. Cis bond does mammals are of cis configuration. Cis bond does not permit rotation around C=C and thus introduce not permit rotation around C=C and thus introduce rigid bend or kink.rigid bend or kink.

2.Trans bond occur naturally and are also produced 2.Trans bond occur naturally and are also produced when unsaturated fatty acids are hydrogenated.when unsaturated fatty acids are hydrogenated.

NOTE Trans bonds have high ,melting point than NOTE Trans bonds have high ,melting point than cis bonds.cis bonds.