Introduction to Lipid

1

Biochemistry of Lipid & Membranes

Dr. Yogesh V. Ushir

16-07-2012

What are lipids?Lipids are chemically diverse groups of

compounds, the common and defining feature of which is their insolubility in water

Lipids are extracted from tissues with organic solvents such as ethyl ether, chloroform, and acetone.

Lipids are condensational product of alcohol and

and their derivatives216-07-2012

fatty acids

Fatty acidsFatty acids are carboxylic acids with

hydrocarbon chains ranging from 4-36 carbons long.

In some fatty acids, this chain is unbranched and fully saturated

In others, the chains can contain one or more double bonds

A few fatty acids contain 3 carbon rings, hydroxyl group, or methyl groups branches

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Nomenclature of fatty acids

Number of double bondPosition of double bond

Carbon chain length

18:3 (Δ 9, 12, 15) The most commonly occurring fatty acids have

even number of carbon atoms in an unbrached chain of 12-24 carbons

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Lipids are non-polar (hydrophobic) compounds, soluble in organic solvents.

Most membrane lipids are amphipathic, having a non-polar end and a polar end.

Fatty acids consist of a hydrocarbon chain with a carboxylic acid at one end.

A 16-C fatty acid: CH3(CH2)14-COO-

Non-polar polar

A 16-C fatty acid with one cis double bond between C atoms 9-10 may be represented as 16:1 cis 9.

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General pattern of double bondsThe most common position for double bonds are

Δ9, Δ12, and Δ15The double bonds of poly saturated fatty

acids are separated by methyl group: -CH=CH-CH2-CH=CH-

In almost all naturally occurring unsaturated fatty acids, the double bonds are cis configuration. eg. N-dodecanoic acid, n-eicosanoic acid

(in Arachis oil)

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Some fatty acids and their common names:14:0 myristic acid; 16:0 palmitic acid; 18:0 stearic acid; 18:1 cis9  oleic acid18:2 cis9,12  linoleic acid18:3 cis9,12,15  -linonenic acid 20:4 cis5,8,11,14  arachidonic acid20:5 cis5,8,11,14,17  eicosapentaenoic acid (an omega-3)

7

Double bonds in fatty acids usually have the cis configuration.

Most naturally occurring fatty acids have an even number of carbon atoms.

C

O

O 1

23

4

fatty acid with a cis-9 double bond

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There is free rotation about C-C bonds in the fatty acid hydrocarbon, except where there is a double bond.

Each cis double bond causes a kink in the chain.

Rotation about other C-C bonds would permit a more linear structure than shown, but there would be a kink.

8

C

O

O 1

23

4

fatty acid with a cis-9 double bond

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Classification of fatty acidsSaturated

Unsaturated

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Saturated fatty acidsRepresented by general formula CH3(CH2)nCOOH

The simplest is the acetic acid where n=0

Does not show double bond in structure

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Some of saturated fatty acids

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Saturated fatty acid

formula Number of C-atom

Acetic acid CH3COOH 0

Butyric acid CH3(CH2)2COOH 4

Caproic acid CH3(CH2)4COOH 6

Lauric acid CH3(CH2)10COOH 12

Myritic acid CH3(CH2)12COOH 14

Palmitic acid CH3(CH2)14COOH 16

Stearic acid CH3(CH2)16COOH 18

Arachidic acid CH3(CH2)18COOH 20

Lignoceric acid CH3(CH2)22COOH 24

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UnSaturated fatty acidsThey contain one or more double bondsSome of them are:

Palmitoleic acidOleic acidLinoleic acidArachidonic acidCyclic fatty acidsProstaglandins

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Physical properties of Fatty acidsThe physical properties of fatty acids are

largely determined by the length and degree of unsaturation of the hydrocarbon chain

The longer the chain and fewer the double bonds, the lower is the solubility in water, and higher the melting point

The lower fatty acid are liquid and higher fatty acids are solid at room temperature

Most of the fatty acids lighter than water

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Chemical properties of Fatty acidsFormation of esters with alcoholsFormation of soaps with alkalies

RCOOH + NaOH ---------------- RCOONa + H2ODetergents

Due to double bond of unsaturated fatty acidsHydrogenationHalogenationOxidation at double bond

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Classification of LipidsBased on their biological functions, lipids can

be classified into:Storage Lipid --- Principle stored form of

energy

Structural Lipids --- The major structural elements of biological membranes

Lipids as signals, cofactors, and pigments

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Storage LipidsStorage lipids include fats and oils, and wax

Fats & oils are composed of three fatty acids each in ester linkage with a single glycerol (Triglycerols)

Waxes are ester of long-chain (C14-C36) saturated and unsaturated fatty acids with long-chain (C16-C30) alcohols

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Lipid as Structural Elements Membrane Lipids

PhospholipidsGlycerophospholipidsSpingolipids

GlycolipidsSpingolipidsGalactolipids/Sulpholipids

Archaebacterial ether lipids

Sterols1716-07-2012

Lipids as Signals, Cofactors, and Pigments

Some lipids, presents in very small amount, have active role in the metabolic traffic as metabolites & messengers. They serve the following functions:As signal molecules

As enzyme cofactors

As pigments

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Based on their chemical structure, lipids can be classified into:Simple Lipid --- Esters of fatty acids with alcohol

Fats & oils waxes

Complex Lipids --- esters of fatty acids with alcohols containing additional groups as, Po4, nitrogenous bases, carbohydrates, proteins etc

Phospholipids Glycerophospholipids Glycolipids Sphingophospholipids Lipoproteins Sulpholipids, aminolipids,

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Derived Lipids Lipid (fat) soluble vitamins Steroid hormones Ketone bodies

Miscellaneous Lipids Carotenoids Squalene Terpenes

NEUTRAL LIPIDS triglycerides

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Simple Lipids

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A. Fats & oils : These are fatty acids esters of the trihydric

alcohol, glycerol.

Are also known as triglycerides or triacylglycerols (TAG)

Glycerols + Fatty Acids ------------- TAG

Most of occurring TAG’s are mixed, which contain 2 or more different fatty acids. TAGs are nonpolar, hydrophobic molecules, essentially insoluble in water

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Identification of Fats & OilsHydrolysisSaponificationSaponification

numberAcid numberIodine number

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Acetyl numberPolenske numberReichert-Miessl

numberHalogenation Rancidity

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B. WaxesWaxes are ester of long-chain (C14-C36)

saturated and unsaturated fatty acids with long-chain (C16-C30) alcohols.

In human body commonest waxes are esters of cholesterol

Three types are;True waxes- esters of higher fatty acids with

acetyl alcohol or other higher straight chain alcohols

Cholesterol esters - are esters of fatty acids with cholesterol

Vit. A & D esters- are palmitic acid or stearic acid esters of vitamin A (Retinol) or vitamin D, respectively

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Functions of WaxChief storage fuels for some microorganisms

Protect skin and hair

Prevent excess water evaporation in plants

Protect against parasites

Application in industries, pharmaceuticals, and Cosmetics

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ExampleBEES WAX- palmitic acid ester of myricyl

alcohol (C30H61OH)

LANOLIN or WOOL FAT- palmitic, oileic or steric acid ester of cholesterol

SPERMACETI- palmitic acid ester of cetyl alcohol (C16H33OH). It is oil from head of whale

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Compound lipids

Most of complex lipids have structural function in cell

membraneGlycero-phospholipidsPhospholipidsSphingo-lipidsMembrane Glyco-lipidsGalacto-lipids/Sulfolipids

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STRCTURE OF CELL MEMBRANE

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A. Phospholipids (phosphatides) Are esters of fatty acids with glycerol

containing an esterified phosphoric acid and an nitrogen base

They are present in large amount in Nervous tissue, brain, liver, kidney, pancrease, and heart

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Functions of PhospholipidsThey increases the rate of fatty acid

oxidationThey act as carriers of inorganic ions across

the membranesThey helps blood clottingThey acts as prosthetic group for certain

enzymesThey forms the structures of membranes,

matrix of cell wall, myelin sheath, microsomes and mitochondria

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Phospholipids (Continu…)

These are lipids that contain one or more phosphate groups

PL are the primary components of biomembranes. Other lipids in biomembranes are glycolipids and cholesterol. Surfactants are phopsholipids, mostly phosphatidylcholine

PL are subclassifiedbased on their parent lipid; phopshoglycerides or sphingomyelins

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PL are subclassifiedbased on their alcohol present in the phospholipidGlycerophosphatides- glycerol is alcohol gr.

phosphatidylserine; phosphatidylcholine (Lecithins); phosphatidy lethanolamine (Cephalin); Diphosphatidylglycerol(cardiolipin)

Phosphoinositides- inisitol is alcohol gr. phosphatidylinositol;

Phosphospingosides- sphingosine is an amino alcohol Sphingomyelins;

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Glycerophospholipids Are Derivatives of Phosphatidic Acid

Glycerophospholipidis named for the head group with the prefix “phosphatidyl-.”

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Glycerophospholipids

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Di-Phosphotidyl glycerolIt is important intermediate form in the

synthesis of TAG’s and PLAnother name is Cardiolipin

Form from Phosphotidyl glycerol Chemically di Phosphotidyl glycerol Present in inner membrane of bacterial wall and

mitochondria

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Phosphatidylcholine Lecithins

Contains glycerols and saturated fatty acids, phosphoric acid and choline (N-base)

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Spingolipids

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Sphingosine is a derivative of glycerol but it has –NH2 instead of -OH at C2 and has a -OH as well as a long chain hydrocarbon on C3

The –NH2 forms an amide bond with a long chain FA to form a ceramide.

Sphigomyelin is formed when a phosphodiester bridge links the C1 -OH of ceramide to ethanolamine or choline

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SpingomyelinsFound large quantities in brain & nervous

tissueThe concentration of this PL are increased

in liver and Spleen; due to metabolic defect called Niemann-Pick’s Disease

Consist sphingol (complex amino alcohol), fatty acids, choline and phosphoric acid

No glycerol is presentSphingomyelins are present in the plasma

membrane of animal cells, especially in myelin, a membrane sheath that insulate the axons of some neurons

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B. Glycolipids

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Contain an amino acid alcohol (Spingosine or iso-spingosine) attached with an amide linkage to a fatty acids and glycosidically to a carbohydrate moiety

Glycolipids are lipids that contain carbohydrates

Two types Cerebrosides Gangliosides

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Cerebrosides have a monosaccharide attached to the C1 -OH of ceramide

Gangliosides have an oligosaccharide attached to theC1 -OH of ceramide

Cerebrosides are found in the brain and Spinal Chord. Chief constituent of myelin sheath

Gangliosides are found in the ganglions of brain

In biomembranes, glycolipids are orientedasymmetrically with the sugar units always on theextracellular side of the membrane

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Other compound lipidsLipoproteins

TAG’s (45%) + PL (35%) + Cholesterols + Cholesterly esters (15%) + FFA (< 5%) and also protein combine to form a hydrophillic lipoprotein complex

4 major gr of LP are identified which are important physiologically & in clinical diagnostic in some metabolic disorders; Chylomicrons VLDL (pre- β-LP) LDL (β-LP) HDL (α-LP)

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AminolipidsPhophatidyl ethanolamine & serine are

aminolipidsSulpholipids

SulphatidesIsolated from brain and other animal tissuesSulfolipids have a sulfonated glucose residue

joined to a diacylglycerol in glycosidic linkage. Theyalso exist predominantly in chloroplasts.

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Derived lipidsThe derived from the simple lipid &

compound lipid hence the name given.

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SteroidsSterols: Cholesterol, Ergosterol, coprosterolBile acids : Glycocholic acid, taurocholic

acidSex harmones: testosterone, estradiolAdrenal cortical hormones: corticosteroneVit. D: Vit. D2 & D3 Cardiac glycosides: strophanthinSaponins: Digitonin

Are the some important derived lipids

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Chemical reactions for derived lipidsSalkowski reaction

Sterol gives red color at the bottom of the test tube when treated with conc. Sulphuric acid

Lieberman-Burchard reaction Sterol gives rose-red color when chloroform

layer treated with acetic anhydride & conc. Sulphuric acid, which rapidely changes to blue & finally green

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CholesterolOne of the important derived lipid

Meaning solid alcohol from bile

Sources- diet: only found in animal fat brain, nervous tissues, adrenal

glands & egg yolk are rich sources

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biosynthesis and degradationbiosynthesis: primarily synthesized in

the liver from acetyl-coA; biosynthesis is inhibited by LDL uptake

degradation: only occurs in the liver

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Properties of cholesterolThe double bond can be saturated by addition

of hydrogen to form the dihydroderivative, it can also be halogenated

The 3 position OH group can be esterified with fatty acids to form cholesterol esters; three fourths of cholesterol of plasma exists as ester

Lanoline the cholesterol ester already studies as under WAXES

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CH3

CH3

H

OH

H3C

HH

hydrophillic

hydrophobic

OR

O

usually palmitate

drawn this way

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Cholesterol and cholesterol esters

HO

HH

Functions: -serves as a component of membranes of cells (increases or

moderates membrane fluidity

-precursor to steroid hormones

-storage and transport – cholesterol esters16-07-2012 50

STEROID NUMBERING SYSTEM

A B

C D1

2

3

45

6

7

89

10

1112

13

14 15

16

1718

19

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Cholesterol is largely hydrophobic.

But it has one polar group, a hydroxyl, making it amphipathic.

C holestero lHO

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Cholesterol, an important constituent of cell membranes, has a rigid ring system and a short branched hydrocarbon tail.

cholesterol

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Cholesterolin membrane

Cholesterol inserts into bilayer membranes with its hydroxyl group oriented toward the aqueous phase & its hydrophobic ring system adjacent to fatty acid chains of phospholipids.

The OH group of cholesterol forms hydrogen bonds with polar phospholipid head groups.

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C holestero lHO

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But the presence of cholesterol in a phospholipid membrane interferes with close packing of fatty acid tails in the crystalline state, and thus inhibits transition to the crystal state.

Phospholipid membranes with a high concentration of cholesterol have a fluidity intermediate between the liquid crystal and crystal states.

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Interaction with the relatively rigid cholesterol decreases the mobility of hydrocarbon tails of phospholipids.

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Functions of cholesterolserves as a component of membranes of

cells (increases or moderates membrane fluidity)

precursor to steroid hormones and bile acids

storage and transport –cholesterol esters

Cholesterolin membrane

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Photograph of an arterial plaque

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Prostaglandins and other eicosanoids (prostanoids)local hormones, unstable, key mediators of

inflammationderivatives of prostanoic acid

COOH

20

8

12

prostanoic acid

9

1115

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O R

O

O

OP

O

O

O-

X

O

COOH

CH3

phospholipase A 2 (enzyme that hydrolyzesat the sn-2 position - inhibitedindirectly by corticosteroids)

H20

prostaglandin synthase(also known as cyclooxygenase)

O

O

COOH

OH

very unstablebond

PGH2

COX is inhibibited byaspirin and other NSAIDs

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O

O

COOH

OH

PGH2

COOH

OH

O

HO

COOH

OHHO

HO

PGE2 PGF2

key mediator of inflammation

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O

R1

R2

O

R1

R2

PGA PGB

O

R1

R2

PGC

R1

R2

HO

OPGD

R1

R2

O

HO

R1

R2

HO

HO

R1

R2

O

O

PGE PGFa PGG and PGHR2

HO

O

R1

R1

R2

O

PGJ

R1

R2

O

O

PGK

PGI

O

O

R1

R2 O

R1

R2HO

OH

TXA TXB

SUBSTITUTION PATTERN OF PROSTANOIDS16-07-2012 61

Prostacyclins, thromboxanes and leukotrienesPGH2 in platelets is converted to

thromboxane A2 (TXA2) a vasoconstrictor which also promotes platelet aggregation

PGH2 in vascular endothelial cells is converted to PGI2, a vasodilator which inhibits platelet aggregation

Aspirin’s irreversible inhibition of platelet COX leads to its anticoagulant effect

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Functions of eicosanoidsProstaglandins – particularly PGE1 – block

gastric production and thus are gastric protection agents

Misoprostol (Cytotec) is a stable PGE1

analog that is used to prevent ulceration by long term NSAID treatment

PGE1 also has vasodilator effectsAlprostadil (PGE1) – used to treat infants with

congenital heart defectsAlso used in impotance (Muse)

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Functions of eicosanoidsPGF2 – causes constriction of the uterus

Carboprost; “Hebamate” (15-Me-PGF2) – induces abortions

PGE2 is applied locally to help induce labor at term

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Examples of drugs derived from prostaglandins

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Terpenessimple lipids, but lack fatty acid componentformed by the combination of 2 or more

molecules of 2-methyl-1,3-butadiene (isoprene)

monoterpene (C-10) – made up of 2 isoprene units

sesquiterpene (C-15) – made up of 3 isoprene units

diterpene (C-20) – made up of 4 isoprene units

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limonene

CHO

citronellal

OH

menthol camphene

Monoterpenes are readily recognized by their characterisitic flavors and odors ( limonene in lemons, citronellal in roses and geraniums, pinene in turpentine and menthol from peppermint)

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bisabolene

HO

eudesmol

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CH2OH

HO

H

H

OH

COOHC

O

CH3

O

phytol gibberelic acid

CH3CH3

H3C

CH3

CH3

O

H

All-trans-retinal

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Triterpenes are C-30 compounds are addition products of 2 sesquiterpenes;

Both squalene and lanosterol are precursors of cholesterol and other steroids

HO

H

squalene lanosterol

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Other terpenestetraterpenes (C-40) are not as common as

mono, di, and triterpenesinclude the carotenoids such as beta-carotene

(precursor of vitamin A) and lycopene found in tomatoes

usually colorful compounds due to highly conjugated system

polyisoprenoids or polyprenols consist of numerous isoprene adducts (8 – 22) examples include dolichol phosphate,

undecaprenyl alcohol (bactoprenol) and the side chains of vitamins K, vitamin E and coenzyme Q

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16-07-2012 72Thank You