introduction to lipids and their chemistry and structure

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LipidsLipids

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Learning objective
 What are lipidslipids, their componentscomponents and their non-polarnon-polar
nature influence their extraction.
 RoleRole of lipids in our daily life.
 Various groups of lipids,groups of lipids, clssification on the basis of
types of alcohols and fatty acids.
 CompositionComposition & importanceimportance of fats, oils and waxes.
 WhatWhat is compound lipids & its various categories.
 Physiological rolePhysiological role & structural formulasformulas of different
glycerophospholipids.
 WhatWhat is sphingophospholipid and composition of
ceramide.

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LipidsLipids
 Naturally occurringNaturally occurring non-polarnon-polar,, water insolublewater insoluble,,
(Hydrophobic) substances found in plants &(Hydrophobic) substances found in plants &
animal tissues which areanimal tissues which are extractibleextractible by non-by non-
polar organic solvents such as:polar organic solvents such as:
methanolmethanol,, ethanolethanol,, acetoneacetone,, chloroformchloroform,, carboncarbon
tetrachloridetetrachloride,, etherether, &, & benzenebenzene..
 The group includesThe group includes fatty acidsfatty acids & many other& many other
allied natural products e.g.allied natural products e.g. steroidssteroids,, terpenesterpenes &&
fat-soluble vitaminsfat-soluble vitamins..

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Importance of lipidsImportance of lipids
 Commercially:Commercially: they are being extensivelythey are being extensively
used in manufacturing ofused in manufacturing of soapssoaps,, detergentsdetergents,,
greasesgreases,, paintspaints etc.etc.
 Biological:Biological:
 1-1- Act asAct as lubricantslubricants in the alimentary canalin the alimentary canal
because of its greasy nature.because of its greasy nature.
 2-2- Provide transportationProvide transportation in combination within combination with
non-polar components e.g.non-polar components e.g. lipids form solublelipids form soluble
complex with proteinscomplex with proteins & transport them from& transport them from
one site to another through blood plasma.one site to another through blood plasma.

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3-3- They are importantThey are important constituent of cellsconstituent of cells &&
tissuestissues e.g. cell membranes, nucleus,e.g. cell membranes, nucleus,
mitochondria, chloroplasts.mitochondria, chloroplasts.
 4-4- They areThey are best combustion materialbest combustion material in thein the
body that providesbody that provides 9 kcal/g9 kcal/g while protein 4while protein 4
kcal/g.kcal/g.
 5-5- Play an important role in the functioning ofPlay an important role in the functioning of
thethe nervous systemnervous system..
 6-6- They provideThey provide essential fatty acidsessential fatty acids throughthrough
the diet.the diet.

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 7-7- Degradation products areDegradation products are important startingimportant starting
materialmaterial for the synthesis of biologicallyfor the synthesis of biologically
important compound e.g.important compound e.g. acetic acidacetic acid (acetate)(acetate)
is the starting material for the biosynthesis ofis the starting material for the biosynthesis of
cholesterolcholesterol..
 8-8- Like fat-soluble vitamins & hormones haveLike fat-soluble vitamins & hormones have
intenseintense biological activitybiological activity && control variouscontrol various
metabolic processmetabolic process..

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Classification of LipidsClassification of Lipids
 1 – Simple lipids
 2 – Compound lipids
 3 – Derived lipids

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1- Simple Lipids:1- Simple Lipids: esters of alcohol & fattyesters of alcohol & fatty
acids such as Fats, oils & waxes.acids such as Fats, oils & waxes.
 a)- Fats & oils are thea)- Fats & oils are the estersesters ofof glycerolglycerol withwith
higherhigher fatty acidsfatty acids..
 Also calledAlso called neutral fatsneutral fats oror triglyceridestriglycerides..
 A new termA new term triglyceroltriglycerol is being used instead ofis being used instead of
triglyceride.triglyceride.
Fatty acid + glycerol fatFatty acid + glycerol fat

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 O O
 CH2 – OH H – O – C – R CH2 – O – C – R
 O O
 CH – OH + H – O – C – R CH – O – C – R
 O O
 CH2 – OH H – O – C – R CH2 – O – C – R
Glycerol Fatty acid Fat

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 b)-b)- Waxes are theWaxes are the estersesters ofof alcoholsalcohols (higher(higher
mol wt) such as acetyl alcohol, cholesterol etcmol wt) such as acetyl alcohol, cholesterol etc
with higherwith higher fatty acidsfatty acids..
 (Cholesterol + fatty acid) called(Cholesterol + fatty acid) called Bees waxBees wax..
 Waxes are commonly known asWaxes are commonly known as lubricantlubricant..
Significance of Waxes
 i- They serve as protective coating on the
surface of animals & plants.
 ii- They protect plants from water loss.
 iii- Skin & feathers are wetted due to wax.

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 iv- Many fruits are prevented from infections.
 v- Industrial waxes are commonly called
lubricants such as candle & ointment.

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 2- Compound Lipids (complex lipids)2- Compound Lipids (complex lipids)
Compounds containing someCompounds containing some chemical moietychemical moiety
in addition to alcohol & fatty acid.in addition to alcohol & fatty acid.
Such as:Such as:
I)- Phospholipids II)- GlycolipidsI)- Phospholipids II)- Glycolipids
III)- Sulpholipids IV)- GangliosidesIII)- Sulpholipids IV)- Gangliosides
V)- Lipoproteins VI)-V)- Lipoproteins VI)-
LipopolysaccharidesLipopolysaccharides

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I)-Phospholipids:I)-Phospholipids:
These are esters ofThese are esters of fatty acidsfatty acids with an alcoholwith an alcohol
which is generallywhich is generally glycerolglycerol & rarely& rarely
sphingosine & asphingosine & a phosphoric acidphosphoric acid is attached tois attached to
it.it.
• These are richly found in brain & nerves, liver,
kidneys, pancreas, heart etc.
• Phosphatidic acid is the mother compound of
phospholipids.

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 Structure of phosphatidic acid.
 O
 O CH2 – O – C – R
 R – C – O - CH O
 CH2 – O – P – OH
 OH
 FA = Phosphoric acid =
 Phospholipids are of two types
 a)- Glycerophospholipids
 b)- Sphingophospholipids

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 a)- Glycerophospholipids:
 These are phospholipids having glycerolglycerol as
alcohol.
 Occurs in all cells of plants & animals.
 Not freely soluble in water.
 Examples:
 I)- Phosphotidyl choline
 II)- Phosphotidyl ethanolamine
 III)- Phosphotidyl serine
 IV)- Phosphotidyl threonine

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 V)- Phosphotidyl inositol
 VI)- Plasmalogen
I) – Phosphotidyl choline
 Also known as LecithinsLecithins.
 Mainly found in association with cell
membrane.
 Nitrogen base cholinecholine is attached with
phosphatidic acidphosphatidic acid.

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Phosphotidyl choline

 CH3
 CH2 – CH2 – N – CH3
 CH3

choline

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 II)- Phosphotidyl Ethanolamine:
 Also known as cephalincephalin & differs from
phosphotidyl choline only that ethanolamineethanolamine
replace choline.
 It act as 22ndnd
messengermessenger & present in smooth
muscles’ cell membrane & in brain.
 Take part in clotting of bloodclotting of blood.
structure

 - CH2 – CH2 – NH2

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 III)- Phosphotidyl Serine:
 Present in skeletal muscles & act as 22ndnd
messengermessenger.
 Serine is attached with phosphoric acid.
Structure

 NH2

 - CH2 – CH - COOH

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 IV)- Phoshotidyl Threonine:
 Also found at neuromuscular junctions in
relation with phosphotitidyl serine.
Structure
 NH2
 - CH – CH - COOH

 CH3

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 V)- Phosphotidyl Inositol:
 In muscles alcohol can be derived in the form
of Myoinositol.
 Inostitol is stereoisomer of myoinositol.
Structure
OH
OHOH
OH
OH

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 VI)- Plasmalogen:
 Constitute about 10% of phospholipids of
brain & muscles.
 Structurally there is an ether linkage instead of
ester at C1. except this difference plasmalogen
resemble phosphotidyl ethanolamine.

CH2 – O – CH = CH – R
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- CH2 – CH2 – NH2

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 b)- Sphingophospholipids:
 These are phospholipids in which alcoholalcohol is
sphingosinesphingosine.
 Sphingophospholipids are foundfound in large
amount in brainbrain & nerve tissuesnerve tissues.
 On hydrolysis yield fatty acid, phosphoric
acid, choline & complex amino alcohol the
sphingosine.
 Combination of fatty acidfatty acid with sphingosinesphingosine is
called ceramideceramide structure.

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structure of sphingosine
 OH
 CH3 – (CH2)12 – CH = CH – CH – CH – CH2 – OH
 NH2

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II)- Glycolipids
 Also called glycosphingolipidsglycosphingolipids.
 Contain fatty acidfatty acid, sphingosine (alcoholalcohol) &
carbohydratecarbohydrate.
 CeramideCeramide structure contain carbohydratecarbohydrate
(glucose or galactose).
 A sugar containing lipids present in cellcell
membranemembrane & in white matter of brainbrain.

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III)- Sulpholipids
 These contain sphingosinesphingosine, a fatty acidfatty acid &
sulphated hexosehexose.
 Also occur in white matter of brainbrain.
 O
 Sphingosine – Galactose – S – OH
 Fatty acid O

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IV)- LipoproteinsIV)- Lipoproteins
 These areThese are lipidlipid containingcontaining proteinsproteins..
 They may be water soluble or fat soluble.They may be water soluble or fat soluble.
 These are in veryThese are in very huge in structurehuge in structure && carrycarry
lipidslipids from one place to another.from one place to another.
 This is alsoThis is also presentpresent inin membranemembrane ofof
mitochondria, endoplasmic reticulum &mitochondria, endoplasmic reticulum &
nucleus.nucleus.
 According to density these areAccording to density these are divideddivided into:into:
 * High-density lipoprotein (* High-density lipoprotein (HDLHDL),),

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 * Intermediate-density lipoprotein (* Intermediate-density lipoprotein (IDLIDL),),
 * Low-density lipoprotein (* Low-density lipoprotein (LDLLDL))

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V)- Lipopolysaccharides
 The exactexact chemical naturenature is not known.
 They occur in the cell wallcell wall of some bacteriasome bacteria.
 ββ--hydroxymyristichydroxymyristic acid occur in some of them
in addition to glucosamineglucosamine & phosphate groupphosphate group.

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3- Derived Lipids
 These are the substances which are either
derivedderived from simple or compoundsimple or compound lipids by
their oxidationoxidation or any other mechanism.
 Such as:Such as:
 Steroids, terpenoids, carotenoids & fat-solubleSteroids, terpenoids, carotenoids & fat-soluble
vitamins.vitamins.
 Steroids: The common steroids of animal
cells are sex hormones, vit D & bile acid.

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 Terpenoids: These are very large & important
compound which are formed by repeating
units of isoprenoids.
 e.g. Rubber, terpenes etc.

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Feed-back Qs
 Define composition of lipids.
 Important starting material for the biosynthesis of cholesterol ?
 Define simple lipids with examples.
 Define compound lipids & classify them.
 Glycerophospholipids having?
 Define cephalin?
 What is the difference between cephalin & plasmalogen.
 What is ceramide?
 Friendly lipoproteins are?

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References & keyReferences & key
 ““Mushtaq Ahmad”, “Dr. M. Rafiq Khan”Mushtaq Ahmad”, “Dr. M. Rafiq Khan”
 ““Harper’s Illustrated Biochemistry”.Harper’s Illustrated Biochemistry”.
 TerpeneTerpene: aromatic hydrocarbon obtained from natural sources.: aromatic hydrocarbon obtained from natural sources.
 Essential Fatty AcidsEssential Fatty Acids (EFA): Poly un-saturated long-chain acids not(EFA): Poly un-saturated long-chain acids not
synthesized in the body & therefore provided through diet – Linoleic acid,synthesized in the body & therefore provided through diet – Linoleic acid,
linolinic acid, archidonic acid.linolinic acid, archidonic acid.
 Glycerol:Glycerol: trihydroxy sugar alcoholtrihydroxy sugar alcohol
 Lecithin:Lecithin: essential component of all cell membranes & for fat metabolismessential component of all cell membranes & for fat metabolism
 Cephalin:Cephalin: Found in brain & nerve tissuesFound in brain & nerve tissues
 22ndnd
messenger:messenger: In many hormone sensitive systems the systemic hormoneIn many hormone sensitive systems the systemic hormone
does not enter the target cell but binds to a receptor and indirectly affectsdoes not enter the target cell but binds to a receptor and indirectly affects
the production of another molecule within the cell,the production of another molecule within the cell,
 Phosphoinositide:Phosphoinositide: phosphorylated inositol-containing compounds, thatphosphorylated inositol-containing compounds, that
play roles in cell activation and calcium mobilizationplay roles in cell activation and calcium mobilization
 Plasmalogen:Plasmalogen: found in nerve fibers, cell membranes of muscle, andfound in nerve fibers, cell membranes of muscle, and
platelets.platelets.
 Cerebrosides:Cerebrosides: found in brain and nervous systemfound in brain and nervous system