Chemistry of Lipids.ppt

Chemistry of Lipids

Chemistry of LipidsChemistry of Lipids

Definition:

• - Lipids are organic compounds formed mainly from alcohol and fatty acids combined together by ester linkage.

CH 2R

Fatty alcoholOH C R

Fatty acidHO

O

+

H2O

CH 2R O C R

O

Esterase (lipase) ester (lipid)

• - Lipids are insoluble in water, but soluble in fat or organic solvents (ether, chloroform, benzene, acetone).

• - Lipids include fats, oils, waxes and related compounds.

• They are widely distributed in nature both in plants and in animals.

Biological Importance of Lipids:1. They are more palatable and storable to unlimited

amount compared to carbohydrates.2. They have a high-energy value (25% of body needs)

and they provide more energy per gram than carbohydrates and proteins but carbohydrates are the preferable source of energy.

3. Supply the essential fatty acids that cannot be synthesized by the body.

4. Supply the body with fat-soluble vitamins (A, D, E and K).

5. They are important constituents of the nervous system.

6. Tissue fat is an essential constituent of cell membrane and nervous system. It is mainly phospholipids in nature that are not affected by starvation.

7-Stored lipids “depot fat” is stored in all human cells acts as:

• A store of energy.• A pad for the internal organs to protect them from

outside shocks.• A subcutaneous thermal insulator against loss of

body heat.8-Lipoproteins, which are complex of lipids and

proteins, are important cellular constituents that present both in the cellular and subcellular membranes.

9-Cholesterol enters in membrane structure and is used for synthesis of adrenal cortical hormones, vitamin D3 and bile acids.

10- Lipids provide bases for dealing with diseases such as obesity, atherosclerosis, lipid-storage diseases, essential fatty acid deficiency, respiratory distress syndrome,

Classification of Lipids

1. Simple lipids (Fats & Waxes)

2. Compound or conjugated lipids

3. Derived Lipids

4. Lipid-associating substances

Fatty alcoholsFatty alcohols

1-Glycerol:• It is a trihydric alcohol (i.e., containing

three OH groups) and has the popular name glycerin.

• It is synthesized in the body from glucose.

• It has the following properties:

1. Colorless viscous oily liquid with sweet taste.

2. On heating with sulfuric acid or KHSO4 (dehydration) it gives acrolein that has a bad odor. This reaction is used for detection of free glycerol or any compound containing glycerol.

CH 2 OH

CH

CH 2 OH

HO

CHO

CH

CH 2

2 H2O

Heating, KHSO4

Glycerol Acrolein

3-It combines with three molecules of nitric acid to form trinitroglycerin (TNT) that is used as explosive and vasodilator.

4-On esterification with fatty acids it gives:• Monoglyceride or monoacyl-glycerol: one

fatty acid + glycerol.• Diglyceride or diacyl-glycerol: two fatty

acids + glycerol.• Triglyceride or triacyl-glycerol: three fatty

acids + glycerol.

5-It has a nutritive value by conversion into glucose and enters in structure of phospholipids.

Uses of GlycerolUses of Glycerol::

1. Glycerol enters in pharmaceutical and cosmetic preparations.

2. Reduces brain edema in cerebrovascular disease.

3. Nitroglycerin is used as vasodilator especially for the coronary arteries, thus it is used in treatment of angina pectoris. Also, enters in explosives manufacturing.

4. Glycerol is used in treatment of glaucoma (increased intraocular pressure)due to its ability to dehydrate the tissue from its water content.

2-Sphingosine:2-Sphingosine:• - It is the alcohol(monohydric) present

in sphingolipids.

• - It is synthesized in the body from serine and palmitic acid.

• It is not positive with acrolein test.

CH CH NH 2

CH 2OH

CHCH(CH 2)12CH 3

OH

Sphingosine

Fatty AcidsDefinitionDefinition: • Fatty acids are aliphatic mono-carboxylic

acids that are mostly obtained from the hydrolysis of natural fats and oils.

• Have the general formula R-(CH2)n-COOH and mostly have straight chain (a few exceptions have branched and heterocyclic chains). In this formula "n" is mostly an even number of carbon atoms (2-34) with a few exceptions that have an odd number.

• Fatty acids are classified according to several bases as follows:

I. According to presence or absence of double bonds they are classified into:

• A-Saturated Fatty Acids

• they contain no double bonds with 2-24 or more carbons.

• They are solid at room temperature except if they are short chained.

• They may be even or odd numbered.

• They have the following molecular formula, CnH2n+1COOH.

Saturated fatty acidsSaturated fatty acids (no double )

A-Short chain Saturated F.A. A-Short chain Saturated F.A. (2-10 (2-10 carbon).carbon).

a-Short chain Saturated volatile F.A.(2-6 carbon).

b- Short chain Saturated non volatile F.A.(7-10 carbon).

B-Long chain Saturated F.AB-Long chain Saturated F.A.(more the10 .(more the10 carbon)carbon)

a-Volatile short-chain fatty acids:

• They are liquid in nature and contain They are liquid in nature and contain ((1-6)1-6) carbon atoms. carbon atoms.

• water-soluble and volatile at room water-soluble and volatile at room temperature, e.g., acetic, butyric, and temperature, e.g., acetic, butyric, and caproic acids.caproic acids.

• Acetic F.A. (2C ) CHAcetic F.A. (2C ) CH33-COOH.-COOH.

• Butyric F.A. (4C ) CHButyric F.A. (4C ) CH33-(CH-(CH22))22-COOH.-COOH.

• Caproic F.A. (6C ) CHCaproic F.A. (6C ) CH33-(CH-(CH22))44-COOH.-COOH.

b-Non-volatile short-chain fatty acidsb-Non-volatile short-chain fatty acids:

• They are solids at room temperature They are solids at room temperature and contain and contain 7-107-10 carbon atoms. carbon atoms.

• They are water-soluble and non-They are water-soluble and non-volatile at room temperature include volatile at room temperature include caprylic and capric F.A.caprylic and capric F.A.

• caprylic (8 C ) CHcaprylic (8 C ) CH33-(CH-(CH22))66-COOH.-COOH.

• Capric (10 C ) CHCapric (10 C ) CH33-(CH-(CH22))88-COOH.-COOH.

B-Long-chain fatty acids: • They contain more than 10 carbon atoms. • They occur in hydrogenated oils, animal fats,

butter and coconut and palm oils. • They are non-volatile and water-insoluble • Include palmitic, stearic, and lignoceric F.A.

• palmitic(16C) CHpalmitic(16C) CH33-(CH-(CH22))1414-COOH-COOH

• stearic (18 C ) CHstearic (18 C ) CH33-(CH-(CH22))1616-COOH -COOH

• lignoceric (24C ) CHlignoceric (24C ) CH33-(CH-(CH22))2222-COOH-COOH

B-Unsaturated Fatty Acids

They contain double bond

• monounsaturated

they contain one double bonds .

(CnH2n-1 COOH)

• polyunsaturated

they contain more the one double bond (CnH2n-more than 1 COOH).

1-Monounsaturated fatty acids:

1-Palmitoleic acid :

• It is found in all fats.

• It is C16:1∆9, i.e., has 16 carbons and one double bond located at carbon number 9 and involving carbon 10.

CHCH33-( CH-( CH22 ) )55CH = CH-(CHCH = CH-(CH22))7 7 –COOH–COOH

2-Oleic acid

• Is the most common fatty acid in Is the most common fatty acid in natural fats. natural fats.

• It is It is C18:1∆9C18:1∆9, i.e., has 18 carbons and , i.e., has 18 carbons and one double bond located at carbon one double bond located at carbon number 9 and involving carbon 10.number 9 and involving carbon 10.

CHCH33-(CH-(CH22))77- CH=CH – (CH- CH=CH – (CH22))77-COOH-COOH

3-Nervonic acid

(Unsaturated lignoceric acid).

• It is found in cerebrosides.

• It is C24:115, i.e., has 24 carbons and one double bond located at carbon number 15 and involving carbon 16.

CHCH33 – (CH – (CH22))77 CH= CH – (CH CH= CH – (CH22))1313- COOH- COOH

2-Polyunsaturated fatty acids :

(Essential fatty acids):

• Definition:

• They are essential fatty acids that can not be synthesized in the human body and must be taken in adequate amounts in the diet.

• They are required for normal growth and metabolism

• Source: vegetable oils such as corn oil, linseed oil, peanut oil, olive oil, cottonseed oil, soybean oil and many other plant oils, cod liver oil and animal fats.

• Deficiency: Their deficiency in the diet leads to nutrition deficiency disease.

• Its symptoms include: poor growth and health with susceptibility to infections, dermatitis, decreased capacity to reproduce, impaired transport of lipids, fatty liver, and lowered resistance to stress.

• Function of Essential Fatty Acids: 1. They are useful in the treatment of atherosclerosis

by help transporting blood cholesterol and lowering it and transporting triglycerides.

2. The hormones are synthesized from them.3. They enter in structure of all cellular and

subcellular membranes and the transporting plasma phospholipids.

4. They are essential for skin integrity, normal growth and reproduction.

5. They have an important role in blood clotting (intrinsic factor).

6. Important in preventing and treating fatty liver.7. Important role in health of the retina and vision.8. They can be oxidized for energy production.

1-Linoleic:1-Linoleic:

• C18:29, 12.

• It is the most important since other essential fatty acids can be synthesized from it in the body.

CHCH33-(CH-(CH22))44-CH = CH-CH-CH = CH-CH22-CH=CH-(CH-CH=CH-(CH22))77--

COOHCOOH

2-Linolenic acid2-Linolenic acid:

• C18:39, 12, 15,

• in corn, linseed, peanut, olive, cottonseed and soybean oils.

CHCH33-CH-CH22-CH=CH-CH-CH=CH-CH22-CH=CH-CH-CH=CH-CH22--

CH=CH-(CHCH=CH-(CH22))77-COOH-COOH

3-Arachidonic acid3-Arachidonic acid:

• C20:45, 8, 11, 14.

• It is an important component of phospholipids in animal and in peanut oil from which prostaglandins are synthesized.

CHCH33-(CH-(CH22))44-CH=CH-CH-CH=CH-CH22-CH=CH-CH-CH=CH-CH22--

CH=CH-CHCH=CH-CH22-CH=CH-(CH-CH=CH-(CH22))33-COOH-COOH

1-Simple LipidsA-Neutral Fats and oilsA-Neutral Fats and oils (Triglycerides) (Triglycerides)Definition:Definition:• - They are called neutral because they - They are called neutral because they

are uncharged due to absence of are uncharged due to absence of ionizable groups in it. ionizable groups in it.

• The neutral fats are the most abundant The neutral fats are the most abundant lipids in nature. They constitute about lipids in nature. They constitute about 98% of the lipids of adipose tissue, 30% 98% of the lipids of adipose tissue, 30% of plasma or liver lipids, less than 10% of plasma or liver lipids, less than 10% of erythrocyte lipids.of erythrocyte lipids.

• They are esters of glycerol with various fatty They are esters of glycerol with various fatty acids. Since the 3 hydroxyl groups of acids. Since the 3 hydroxyl groups of glycerol are esterified, the neutral fats are glycerol are esterified, the neutral fats are also called also called “Triglycerides”.“Triglycerides”.

• Esterification of glycerol with one molecule Esterification of glycerol with one molecule of fatty acid gives of fatty acid gives monoglyceridemonoglyceride, and that , and that with 2 molecules gives with 2 molecules gives diglyceridediglyceride..

H2C O

C HO

H2C

C

C

O C

R1

R3

R2

O

O

O

+

3 H2O

CH 2 OH

C HHO

CH 2 OH

HO C R1

O

HO C R3

O

HO C R2

O

Fatty acids Glycerol Triglycerides(Triacylglycerol)

Types of triglyceridesTypes of triglycerides

1-Simple triglycerides1-Simple triglycerides: If the three fatty acids : If the three fatty acids connected to glycerol are of the same type connected to glycerol are of the same type the triglyceride is called simple triglyceride, the triglyceride is called simple triglyceride, e.g., tripalmitin.e.g., tripalmitin.

2-Mixed triglycerides2-Mixed triglycerides: if they are of different : if they are of different types, it is called mixed triglycerides, e.g., types, it is called mixed triglycerides, e.g., stearo-diolein and palmito-oleo-stearin.stearo-diolein and palmito-oleo-stearin.

• Natural fats are mixtures of mixed Natural fats are mixtures of mixed triglycerides with a small amount of simple triglycerides with a small amount of simple triglycerides.triglycerides.

CH 2 O

C HO

CH 2

C

C

O C

(CH 2)14

O

O

O

Tripalmitin(simple triacylglycerol)

CH 3

(CH 2)14CH 3

(CH 2)14 CH 3

CH 2 O

C HO

CH 2

C

C

O C

(CH 2)16

O

O

O

1-Stearo-2,3-diolein(mixed triacylglycerol)

CH 3

(CH 2)7CHCH(CH 2)7CH 3

(CH 2)7 CH CH (CH 2)7 CH 3

CH 2 O

C HO

CH 2

C

C

O C

(CH 2)14

O

O

O

1-palmito-2-oleo-3-stearin(mixed triacylglycerol)

CH 3

(CH 2)16 CH 3

(CH 2)7CHCH(CH 2)7CH 3

• The commonest fatty acids in The commonest fatty acids in animal fats are animal fats are palmitic, stearic palmitic, stearic and oleic acids. and oleic acids.

• The main difference between fats The main difference between fats and oils is for and oils is for oils being liquidoils being liquid at at room temperature, whereas, room temperature, whereas, fats fats are solids.are solids.

• This is mainly due to presence of This is mainly due to presence of larger percentage of larger percentage of unsaturated unsaturated fatty acids in oils than fats that has fatty acids in oils than fats that has mostly mostly saturatedsaturated fatty acids. fatty acids.

Physical properties of fat and oils:Physical properties of fat and oils:1. Freshly prepared fats and oils are

colorless, odorless and tasteless.Any color, or taste is due to association with other foreign substances, e.g., the yellow color of body fat or milk fat is due to carotene pigments(cow milk).

2. Fats have specific gravity less than 1 and, therefore, they float on water.

3. Fats are insoluble in water, but soluble in organic solvents as ether and benzene.

4. Melting points of fats are usually low, but higher than the solidification point,

Chemical Properties of fats and oilsChemical Properties of fats and oils:

1-Hydrolysis:1-Hydrolysis:• They are hydrolyzed into their constituents (They are hydrolyzed into their constituents (fatty fatty

acids and glycerol)acids and glycerol) by the action of super heated by the action of super heated steam, acid, alkali or enzyme (e.g., lipase of steam, acid, alkali or enzyme (e.g., lipase of pancreas). pancreas).

• - During their enzymatic and acid hydrolysis glycerol - During their enzymatic and acid hydrolysis glycerol and free fatty acids are produced. and free fatty acids are produced.

CH 2 O

C HO

CH 2

C

C

O C

R1

R3

R2

O

O

O

3 H2O

H2C OH

C HHO

H2C OH

OHCR1

O

OHCR3

O

+ OHCR2

OLipase or Acid

Triacylglycerol Glycerol Free fatty acids

2-Saponification. Alkaline hydrolysis Alkaline hydrolysis produces glycerol and salts of fatty acids produces glycerol and salts of fatty acids ((soapssoaps).).

• Soaps cause emulsification of oily material Soaps cause emulsification of oily material this help easy washing of the fatty materialsthis help easy washing of the fatty materials

CH 2 O

C HO

CH 2

C

C

O C

R1

R3

R2

O

O

OH2C OH

C HHO

H2C OH

ONaCR1

O

ONaCR3

O

+ ONaCR2

O

Triacylglycerol Glycerol Sodium salts of fatty acids (soap)

3 NaOH

3-Halogenation3-Halogenation• Neutral fats containing unsaturated fatty acids have Neutral fats containing unsaturated fatty acids have

the ability of adding halogens (e.g., hydrogen or the ability of adding halogens (e.g., hydrogen or hydrogenation and iodine or iodination) at the hydrogenation and iodine or iodination) at the double bonds.double bonds.

• - It is a very important property to determine the - It is a very important property to determine the degree of unsaturation of the fat or oil that degree of unsaturation of the fat or oil that determines its biological value determines its biological value

CH (CH 2)7 COO HCHCH2CH

Linoleic acidCH(CH 2)4CH3

2 I2

CH (CH 2)7 COO HCHCH2CH

Stearate-tetra-iodinate

CH(CH 2)4CH3

II I I

4-Hydrogenation or hardening of oils4-Hydrogenation or hardening of oils: • It is a type of addition reactions accepting It is a type of addition reactions accepting

hydrogen at the double bonds of unsaturated hydrogen at the double bonds of unsaturated fatty acids.fatty acids.

• The hydrogenation is done under high The hydrogenation is done under high pressure of hydrogen and is catalyzed by pressure of hydrogen and is catalyzed by finely divided nickel or copper and heat. finely divided nickel or copper and heat.

• It is the base of hardening of oils (It is the base of hardening of oils (margarine margarine manufacturingmanufacturing), e.g., change of oleic acid of ), e.g., change of oleic acid of fats (liquid) into stearic acid (solid).fats (liquid) into stearic acid (solid).

• It is advisable not to saturate all double It is advisable not to saturate all double bonds; otherwise margarine produced will be bonds; otherwise margarine produced will be very hard, of very low biological value and very hard, of very low biological value and difficult to digest.difficult to digest.

Advantages for hydrogenated oil or fat are as follows:1.1. It is more pleasant as cooking fat.It is more pleasant as cooking fat.2.2. It is digestible and utilizable as normal animal fats It is digestible and utilizable as normal animal fats

and oils.and oils.3.3. It is less liable to cause gastric or intestinal It is less liable to cause gastric or intestinal

irritation.irritation.4.4. It is easily stored and transported and less liable to It is easily stored and transported and less liable to

rancidity.rancidity. Disadvantages of hydrogenatedDisadvantages of hydrogenated • fats include lack of fat-soluble vitamins (A, D, E and fats include lack of fat-soluble vitamins (A, D, E and

K) and essential fatty acidsK) and essential fatty acids

Oils(liquid)

(with unsaturated fatty acids, e.g., oleic)

Hard fat(margarine, solid)(with saturated

fatty acids, e.g., stearic)

Hydrogen, high pressure, nickel

5-Oxidation(Rancidty)5-Oxidation(Rancidty)

• This toxic reaction of triglycerides leads to unpleasant odour or taste of oils and fats developing after oxidation by oxygen of air, bacteria, or moisture.

• Also this is the base of the drying oils after exposure to atmospheric oxygen.

Example is linseed oil, which is used in paints and varnishes manufacturing

RancidityRancidityDefinition:Definition:• It is a physico-chemical change in the It is a physico-chemical change in the

natural properties of the fat leading to natural properties of the fat leading to the development of the development of unpleasant odor or unpleasant odor or taste or abnormal colortaste or abnormal color particularly on particularly on aging after exposure to atmospheric aging after exposure to atmospheric oxygen, light, moisture, bacterial or oxygen, light, moisture, bacterial or fungal contamination and/or heat. fungal contamination and/or heat.

• Saturated fats resist rancidity more Saturated fats resist rancidity more than unsaturated fats that have than unsaturated fats that have unsaturated double bonds.unsaturated double bonds.

Types and causes of RancidityTypes and causes of Rancidity:

1.1. Hydrolytic rancidityHydrolytic rancidity2.2. Oxidative rancidityOxidative rancidity3.3. Ketonic rancidityKetonic rancidity1-Hydrolytic rancidity1-Hydrolytic rancidity:• It results from slight hydrolysis of the fat It results from slight hydrolysis of the fat

by lipase from bacterial contamination by lipase from bacterial contamination leading to the liberation of free fatty acids leading to the liberation of free fatty acids and glycerol at high temperature and and glycerol at high temperature and moisture. moisture.

• Volatile short-chain fatty acids have Volatile short-chain fatty acids have unpleasant odor.unpleasant odor.

CH 2 O

C HO

CH 2

C

C

O C

R1

R3

R2

O

O

O

3 H2O

H2C OH

C HHO

H2C OH

OHCR1

O

OHCR3

O

+ OHCR2

OLipase

Triacylglycerol Glycerol Free fatty acids(volatile, bad odor)

2-Oxidative Rancidity2-Oxidative Rancidity: • It is oxidation of fat or oil catalyzed by It is oxidation of fat or oil catalyzed by

exposure to oxygen, light and/or heat exposure to oxygen, light and/or heat producing peroxide derivatives which producing peroxide derivatives which on decomposition give substances, on decomposition give substances, e.g., e.g., peroxides, aldehydes, ketones and peroxides, aldehydes, ketones and dicarboxylic acids that are toxic and dicarboxylic acids that are toxic and have bad odor.have bad odor.

• This occurs due to oxidative addition of This occurs due to oxidative addition of oxygen at the unsaturated double bond oxygen at the unsaturated double bond of unsaturated fatty acid of oils.of unsaturated fatty acid of oils.

Polyunsaturated fatty acid

Peroxyradical

Oxidant, O2

Hydroperoxide

Hydroxy fatty acid

Cyclic peroxide

Aldehydessuch as malondialdehyde

Other fragmentssuch as dicarboxylic acids

3-Ketonic Rancidity:

• It is due to the contamination with It is due to the contamination with certain fungi such as Asperigillus Niger certain fungi such as Asperigillus Niger on fats such as coconut oil.on fats such as coconut oil.

• Ketones, fatty aldehydes, short chain Ketones, fatty aldehydes, short chain fatty acids and fatty alcohols are fatty acids and fatty alcohols are formed. formed.

• Moisture accelerates ketonic rancidity.Moisture accelerates ketonic rancidity.

• Prevention of rancidity is achieved by:Prevention of rancidity is achieved by:1.1. Avoidance of the causes (Avoidance of the causes (exposure to light, exposure to light,

oxygen, moisture, high temperature and oxygen, moisture, high temperature and bacteria or fungal contaminationbacteria or fungal contamination). By ). By keeping fats or oils in well-closed containers keeping fats or oils in well-closed containers in cold, dark and dry place (i.e., in cold, dark and dry place (i.e., good good storage conditions).storage conditions).

2.2. Removal of catalysts such as lead and Removal of catalysts such as lead and copper that catalyze rancidity.copper that catalyze rancidity.

3.3. Addition of Addition of anti-oxidantsanti-oxidants to prevent to prevent peroxidation in fat (i.e., rancidity). They peroxidation in fat (i.e., rancidity). They include phenols, naphthols, tannins and include phenols, naphthols, tannins and hydroquinones. hydroquinones. The most common natural The most common natural antioxidant is vitamin E that is important antioxidant is vitamin E that is important in in vitrovitro and and in vivoin vivo..

Hazards of Rancid Fats:

1.1. The products of rancidity are toxic, The products of rancidity are toxic, i.e., causes food poisoning and i.e., causes food poisoning and cancer.cancer.

2.2. Rancidity destroys the fat-soluble Rancidity destroys the fat-soluble vitamins (vitamins A, D, K and E).vitamins (vitamins A, D, K and E).

3.3. Rancidity destroys the Rancidity destroys the polyunsaturated essential fatty acids.polyunsaturated essential fatty acids.

4.4. Rancidity causes economical loss Rancidity causes economical loss because rancid fat is inedible.because rancid fat is inedible.

Analysis and Identification of fats and oilsAnalysis and Identification of fats and oils

(Fat Constants(Fat Constants))• Fat constants or numbers are tests used Fat constants or numbers are tests used

for:for:

1.1. Checking the purity of fat for detection of Checking the purity of fat for detection of adulteration.adulteration.

2.2. To quantitatively estimate certain properties To quantitatively estimate certain properties of fat.of fat.

3.3. To identify the biological value and natural To identify the biological value and natural characteristics of fat.characteristics of fat.

4.4. Detection of fat rancidity and presence of Detection of fat rancidity and presence of toxic hydroxy fatty acids.toxic hydroxy fatty acids.

1-Iodine number1-Iodine number (or value):• Definition: It is the number of grams of

iodine absorbed by 100 grams of fat or oil.

• Uses: It is a measure for the degree of unsaturation of the fat, as a natural property for it.

• Unsaturated fatty acids absorb iodine at their double bonds, therefore, as the degree of unsaturation increases iodine number and hence biological value of the fat increase.

• It is used for identification of the type of fat, detection of adulteration and determining the biological value of fat.

2-Saponification number (or value):• DefinitionDefinition: It is the number of It is the number of milligrams ofmilligrams of

KOHKOH required to completely saponify required to completely saponify one one gramgram of fat of fat.

• UsesUses: • Since each carboxyl group of a fatty acid Since each carboxyl group of a fatty acid

reacts with one mole of KOH during reacts with one mole of KOH during saponification, therefore, saponification, therefore, the amount of alkali the amount of alkali needed to saponify certain weight of fat needed to saponify certain weight of fat depends upon the number of fatty acids depends upon the number of fatty acids present per weight.present per weight.

• Thus, fats containing short-chain acids will Thus, fats containing short-chain acids will have more carboxyl groups per gram than have more carboxyl groups per gram than long chain fatty acids and consume more long chain fatty acids and consume more alkali, i.e., will have higher saponification alkali, i.e., will have higher saponification number.number.

3-Acids Number3-Acids Number (or value):

• DefinitionDefinition: :

• It is the number of It is the number of milligrams of KOHmilligrams of KOH required to neutralize the free fatty required to neutralize the free fatty acids present in acids present in one gramone gram of fat. of fat.

• Uses:Uses:

• It is used for detection of hydrolytic It is used for detection of hydrolytic rancidity because it measures the rancidity because it measures the amount of free fatty acids present.amount of free fatty acids present.

4-Reichert- Meissl Number4-Reichert- Meissl Number (or value):• DefinitionDefinition: It is the number of : It is the number of milliliters ofmilliliters of 0.1 0.1

NN KOHKOH required to neutralize the water- required to neutralize the water-soluble fatty acids distilled from soluble fatty acids distilled from 5 grams5 grams of of fat. Short-chain fatty acid (less than 10 fat. Short-chain fatty acid (less than 10 carbons) is distillated by steam.carbons) is distillated by steam.

• UsesUses: This studies the natural composition : This studies the natural composition of the fat and is used for detection of fat of the fat and is used for detection of fat adulteration.adulteration.

• Butter that has high percentage of short-Butter that has high percentage of short-chain fatty acids has highest Reichert-Meissl chain fatty acids has highest Reichert-Meissl number compared to margarine. number compared to margarine.

5-Acetyl Number5-Acetyl Number (or value):• DefinitionDefinition: It is number of It is number of milligrams ofmilligrams of KOH KOH

needed to neutralize the acetic acid liberated needed to neutralize the acetic acid liberated from hydrolysis of from hydrolysis of 1 gram of acetylated fat1 gram of acetylated fat (hydroxy fat reacted with acetic anhydride(hydroxy fat reacted with acetic anhydride).

• Uses:Uses: The natural or rancid fat that contains The natural or rancid fat that contains fatty acids with free hydroxyl groups are fatty acids with free hydroxyl groups are converted into acetylated fat by reaction with converted into acetylated fat by reaction with acetic anhydride. acetic anhydride.

• Thus, acetyl number is a measure of number Thus, acetyl number is a measure of number of hydroxyl groups present. of hydroxyl groups present.

• It is used for studying the natural properties It is used for studying the natural properties of the fat and to detect of the fat and to detect adulteration adulteration and and rancidity.rancidity.

B-WaxesB-Waxes• DefinitionDefinition: Waxes are solid simple lipids Waxes are solid simple lipids

containing a monohydric alcohol (with a containing a monohydric alcohol (with a higher molecular weight than glycerol) higher molecular weight than glycerol) esterified to long-chain fatty acids. Examples esterified to long-chain fatty acids. Examples of these alcohols are of these alcohols are palmitoyl alcohol, palmitoyl alcohol, cholesterol, vitamin A or D.cholesterol, vitamin A or D.

• Properties of waxesProperties of waxes: Waxes are insoluble in : Waxes are insoluble in water, but soluble in fat solvents and are water, but soluble in fat solvents and are negative for acrolein test. negative for acrolein test.

• Waxes are not easily hydrolyzed as the fats Waxes are not easily hydrolyzed as the fats and are indigestible by lipases and are very and are indigestible by lipases and are very resistant to rancidity. resistant to rancidity.

• Thus they are of no nutritional value.Thus they are of no nutritional value.

Type of WaxesType of Waxes:• - Waxes are widely distributed in nature such as

the secretion of certain insects as bees-wax, protective coatings of the skins and furs of animals and leaves and fruits of plants. They are classified into true-waxes and wax-like compounds as follows:

A-True waxesA-True waxes: include:• Bees-waxBees-wax is secreted by the honeybees that

use it to form the combs. It is a mixture of waxes with the chief constituent is mericyl palmitate.

B-Wax-like compounds: • Cholesterol estersCholesterol esters: Lanolin (or wool fat) Lanolin (or wool fat)

is prepared from the wool-associated skin is prepared from the wool-associated skin glands and is secreted by sebaceous glands and is secreted by sebaceous glands of the skin. glands of the skin.

• It is very complex mixture, contains both It is very complex mixture, contains both free and esterified cholesterol, e.g., free and esterified cholesterol, e.g., cholesterol-palmitate and other sterolscholesterol-palmitate and other sterols.

C15H31 C OHO

+C30H61OH C15H31 C OO

C30H61

H2OPalmiticacid

Mericylalcohol

Mericylpalmitate

Differences between neutral lipids and waxes:

Waxes Neutral lipidsNeutral lipids

1.1.Digestibility:Digestibility: Indigestible (not Indigestible (not hydrolyzed by lipase).hydrolyzed by lipase).

Digestible (hydrolyzed by lipase).Digestible (hydrolyzed by lipase).

2-Type of 2-Type of alcoholalcohol::

Long-chain monohydric Long-chain monohydric alcohol + one fatty acid.alcohol + one fatty acid.

Glycerol (trihydric) + 3 fatty acidsGlycerol (trihydric) + 3 fatty acids

3-Type of fatty 3-Type of fatty acidsacids::

Fatty acid mainly palmitic Fatty acid mainly palmitic or stearic acid.or stearic acid.

Long and short chain fatty acids.Long and short chain fatty acids.

4-Acrolein test4-Acrolein test: Negative.Negative. Positive.Positive.

5-Rancidability:5-Rancidability: Never get rancid.Never get rancid. Rancidible.Rancidible.

6-Nature at 6-Nature at room room temperaturetemperature.

Hard solid.Hard solid. Soft solid or liquid.Soft solid or liquid.

7-Saponification7-Saponification Nonsaponifiable.Nonsaponifiable. Saponifiable.Saponifiable.

8-Nutritive 8-Nutritive valuevalue:

No nutritive value.No nutritive value. Nutritive.Nutritive.

9-Example:9-Example: Bee & carnuba waxes.Bee & carnuba waxes. Butter and vegetable oils.Butter and vegetable oils.

2-Compound Lipids2-Compound LipidsDefinitionDefinition:• They are lipids that contain additional They are lipids that contain additional

substances, e.g., sulfur, phosphorus, amino substances, e.g., sulfur, phosphorus, amino group, carbohydrate, or proteins beside group, carbohydrate, or proteins beside fatty acid and alcohol.fatty acid and alcohol.

• Compound or conjugated lipids are Compound or conjugated lipids are classified into the following types according classified into the following types according to the nature of the additional group:to the nature of the additional group:

1.1. PhospholipidsPhospholipids2.2. Glycolipids.Glycolipids.3.3. LipoproteinsLipoproteins4.4. Sulfolipids and amino lipids.Sulfolipids and amino lipids.

A-PhospholipidsA-PhospholipidsDefinition:Definition: Phospholipids or phosphatides are Phospholipids or phosphatides are

compound lipids, which contain phosphoric acid compound lipids, which contain phosphoric acid group in their structuregroup in their structure. .

ImportanceImportance: 1.1. They are present in large amounts in the liver and They are present in large amounts in the liver and

brain as well as blood. Every animal and plant cell brain as well as blood. Every animal and plant cell contains phospholipids. contains phospholipids.

2.2. The membranes bounding cells and subcellular The membranes bounding cells and subcellular organelles are composed mainly of phospholipids. organelles are composed mainly of phospholipids. Thus, the transfer of substances through these Thus, the transfer of substances through these membranes is controlled by properties of membranes is controlled by properties of phospholipids.phospholipids.

3.3. They are important components of the lipoprotein They are important components of the lipoprotein coat essential for secretion and transport of plasma coat essential for secretion and transport of plasma lipoprotein complexes. Thus, they are lipotropic lipoprotein complexes. Thus, they are lipotropic agents that agents that prevent fatty liverprevent fatty liver..

4.4. Myelin sheath of nerves is rich with phospholipids.Myelin sheath of nerves is rich with phospholipids.

5-Important in digestion and absorption of 5-Important in digestion and absorption of neutral lipids and excretion of cholesterol neutral lipids and excretion of cholesterol in the bile.in the bile.

6-Important function in blood clotting and 6-Important function in blood clotting and platelet aggregation.platelet aggregation.

7-They provide lung alveoli with 7-They provide lung alveoli with surfactants surfactants that prevent its irreversible collapsethat prevent its irreversible collapse..

8-Important role in signal transduction across 8-Important role in signal transduction across the cell membrane.the cell membrane.

9-Phospholipase A2 in snake venom 9-Phospholipase A2 in snake venom hydrolyses membrane phospholipids into hydrolyses membrane phospholipids into hemolytic lysolecithin or lysocephalin.hemolytic lysolecithin or lysocephalin.

10-They are source of polyunsaturated fatty 10-They are source of polyunsaturated fatty acids for synthesis of acids for synthesis of eicosanoids.eicosanoids.

Sources:Sources: They are found in all cells (plant They are found in all cells (plant and animal), milk and egg-yolk in the and animal), milk and egg-yolk in the form of lecithins.form of lecithins.

StructureStructure: phospholipids are composed of:phospholipids are composed of:

1.1. Fatty acidsFatty acids (a saturated and an (a saturated and an unsaturated fatty acid).unsaturated fatty acid).

2.2. Nitrogenous baseNitrogenous base (choline, serine, (choline, serine, threonine, or ethanolamine).threonine, or ethanolamine).

3.3. Phosphoric acid.Phosphoric acid.4.4. Fatty alcoholsFatty alcohols (glycerol, inositol or (glycerol, inositol or

sphingosine).sphingosine).

• Classification of PhospholipidsClassification of Phospholipids are are classified into 2 groups according to the classified into 2 groups according to the type of the type of the alcoholalcohol present into two types: present into two types:

A-A-GlycerophospholipidsGlycerophospholipids: They are regarded as They are regarded as derivatives of phosphatidic acids that are the derivatives of phosphatidic acids that are the simplest type of phospholipids and include:simplest type of phospholipids and include:

1.1. Phosphatidic acidsPhosphatidic acids..2.2. LecithinsLecithins3.3. CephalinsCephalins..4.4. PlasmalogensPlasmalogens..5.5. InositidesInositides..6.6. CardiolipinCardiolipin.

B-SphingophospholipidsB-Sphingophospholipids: They contain They contain sphingosine as an alcohol and are named sphingosine as an alcohol and are named SphingomyelinsSphingomyelins.

A-GlycerophospholipidsA-Glycerophospholipids 1-Phosphatidic acids:1-Phosphatidic acids:They are metabolic intermediates They are metabolic intermediates

in synthesis of triglycerides and in synthesis of triglycerides and glycerophospholipids in the body and may have glycerophospholipids in the body and may have function as a function as a second messengersecond messenger. They exist in two . They exist in two forms according to the position of the phosphateforms according to the position of the phosphate

CH2 O

C HO

CH2

C

C

O P

R1

R2

O

O

-Phosphatidic acid

OH

OH

O

Saturatedfatty acidPolyunsaturated

fatty acid

Phosphate

CH2 O

C H

CH2

C

O

R1

O

-Phosphatidic acid

Saturatedfatty acid

Polyunsaturatedfatty acid

Phosphate PHO

OH

O

C R2

O

O

2-Lecithins:2-Lecithins:• DefinitionDefinition: Lecithins are Lecithins are

glycerophospholipids that contain choline as glycerophospholipids that contain choline as a base beside phosphatidic acid. They exist a base beside phosphatidic acid. They exist in 2 forms in 2 forms - and - and -lecithins. Lecithins are a -lecithins. Lecithins are a common cell constituent obtained from brain common cell constituent obtained from brain ((-type), egg yolk (-type), egg yolk (-type), or liver (both -type), or liver (both types). Lecithins are important in the types). Lecithins are important in the metabolism of fat by the liver.metabolism of fat by the liver.

• Structure:Structure: Glycerol is connected at C2 or C3 Glycerol is connected at C2 or C3 with a polyunsaturated fatty acid, at C1 with with a polyunsaturated fatty acid, at C1 with a saturated fatty acid, at C3 or C2 by a saturated fatty acid, at C3 or C2 by phosphate to which the choline base is phosphate to which the choline base is connected. The common fatty acids in connected. The common fatty acids in lecithins are stearic, palmitic, oleic, linoleic, lecithins are stearic, palmitic, oleic, linoleic, linolenic, clupandonic or arachidonic acids.linolenic, clupandonic or arachidonic acids.

LysolecithinLysolecithin causes hemolysis of RBCs. This partially causes hemolysis of RBCs. This partially explains toxic the effect of snake venom,. The explains toxic the effect of snake venom,. The venom contains venom contains lecithinaselecithinase, which hydrolyzes the , which hydrolyzes the polyunsaturated fatty converting lecithin into polyunsaturated fatty converting lecithin into lysolecithin. Lysolecithins are intermediates in lysolecithin. Lysolecithins are intermediates in

metabolism of phospholipidsmetabolism of phospholipids.

CH2 O

C HO

CH2

C

C

O P

R1

R2

O

O

-Lecithin

O

OH

O

CH2 O

C H

CH2

C

O

R1

O

-Lecithin

P

OH

O

C R2

O

CH2 CH2 N

CH3

CH3

CH3

+

OCH2CH2N

CH3

CH3

CH3

+

Choline

CholineO

• Lung surfactantLung surfactant • Is a complex of dipalmitoyl-lecithin, sphingomyelin Is a complex of dipalmitoyl-lecithin, sphingomyelin

and a group of apoproteins called apoprotein A, B, and a group of apoproteins called apoprotein A, B, C, and D. C, and D.

• It is produced by type II alveolar cells and is It is produced by type II alveolar cells and is anchored to the alveolar surface of type II and I anchored to the alveolar surface of type II and I cells. cells.

• It lowers alveolar surface tension and improves It lowers alveolar surface tension and improves gas exchange besides activating macrophages to gas exchange besides activating macrophages to kill pathogens. kill pathogens.

• In premature babies, this surfactant is deficient In premature babies, this surfactant is deficient and they suffer from and they suffer from respiratory distress respiratory distress syndromesyndrome. .

• Glucocorticoids increase the synthesis of the Glucocorticoids increase the synthesis of the surfactant complex and promote differentiation of surfactant complex and promote differentiation of lung cells.lung cells.

3-Cephalins (or Kephalins):3-Cephalins (or Kephalins):

• DefinitionDefinition: They are phosphatidyl-They are phosphatidyl-ethanolamine or serine. Cephalins ethanolamine or serine. Cephalins occur in association with lecithins in occur in association with lecithins in tissues and are isolated from the brain tissues and are isolated from the brain ((Kephale = head).Kephale = head).

• StructureStructure: Cephalins resemble lecithins : Cephalins resemble lecithins in structure except that choline is in structure except that choline is replaced by ethanolamine, serine or replaced by ethanolamine, serine or threonine amino acids.threonine amino acids.

• Certain cephalins are constituents of the complex Certain cephalins are constituents of the complex mixture of phospholipids, cholesterol and fat that mixture of phospholipids, cholesterol and fat that constitute the lipid component of the lipoprotein constitute the lipid component of the lipoprotein ““thromboplastinthromboplastin” which accelerates the clotting of ” which accelerates the clotting of blood by activation of prothrombin to thrombin in blood by activation of prothrombin to thrombin in presence of calcium ionspresence of calcium ions.

CH 2 O

C HO

CH 2

C

C

O P

R1

R2

O

O

-Cephalin

O

OH

O

CH 2 CH 2 NH 2 Ethanolamine

HO CH 2 CH COO H Serine

NH 2

HO CH CH COO H Threonine

NH 2CH 3

4-Plasmalogens:4-Plasmalogens:• Definition:Definition: Plasmalogens are found in the cell Plasmalogens are found in the cell

membrane phospholipids fraction of brain membrane phospholipids fraction of brain and muscle (10% of it is plasmalogens), liver, and muscle (10% of it is plasmalogens), liver, semen and eggs.semen and eggs.

• StructureStructure: Plasmalogens resemble lecithins Plasmalogens resemble lecithins and cephalins in structure but differ in the and cephalins in structure but differ in the presence of presence of ,,-unsaturated fatty alcohol-unsaturated fatty alcohol rather than a fatty acid at C1 of the glycerol rather than a fatty acid at C1 of the glycerol connected by ether bond. connected by ether bond.

• At C2 there is an unsaturated long-chain At C2 there is an unsaturated long-chain fatty acid, however, it may be a very short-fatty acid, however, it may be a very short-chain fatty acid chain fatty acid

• Properties: Similar to lecithinsSimilar to lecithins.

CH 2

C HO

CH 2

C

O P

R2

O

-Plasmalogen

O

OH

O

CH 2 CH 2 N

CH 3

CH 3

CH 3

+

-Unsaturatedfatty alcoholCH CH R1O

5-Inositides5-Inositides:• DefinitionDefinition:: • - They are phosphatidyl inositol.They are phosphatidyl inositol. • StructureStructure: They are similar to lecithins or cephalins They are similar to lecithins or cephalins

but they have the cyclic sugar alcohol, but they have the cyclic sugar alcohol, inositol inositol as as the base. They are formed of glycerol, one saturated the base. They are formed of glycerol, one saturated fatty acid, one unsaturated fatty acid, phosphoric fatty acid, one unsaturated fatty acid, phosphoric acid and inositolacid and inositol

CH2

C HO

CH2

C

O P

R2

O

-Phosphatidylinositol

O

OH

O

C R1OO

H

H

OHOH

HOH

H

OHOH

H H1

2 3

4

56

• SourceSource: Brain tissuesBrain tissues.• FunctionFunction: • Phosphatidyl inositol is a major component Phosphatidyl inositol is a major component

of cell membrane phospholipids particularly of cell membrane phospholipids particularly at the inner leaflet of it. at the inner leaflet of it.

• They play a major role as second They play a major role as second messengers during signal transduction for messengers during signal transduction for certain hormone.. certain hormone..

• On hydrolysis by phospholipase C, On hydrolysis by phospholipase C, phosphatidyl-inositol-4,5-diphosphate phosphatidyl-inositol-4,5-diphosphate produces produces diacyl-glycerol and inositol-diacyl-glycerol and inositol-triphosphatetriphosphate both act to liberate calcium both act to liberate calcium from its intracellular stores to mediate the from its intracellular stores to mediate the hormone effects.hormone effects.

6-Cardiolipins:6-Cardiolipins:

• DefinitionDefinition: They are diphosphatidyl-glycerol. They They are diphosphatidyl-glycerol. They are found in the inner membrane of mitochondria are found in the inner membrane of mitochondria initially isolated from heart muscle (cardio). It is initially isolated from heart muscle (cardio). It is formed of 3 molecules of glycerol, 4 fatty acids and 2 formed of 3 molecules of glycerol, 4 fatty acids and 2

phosphate groupsphosphate groups..• FunctionFunction: : Used in serological diagnosis of Used in serological diagnosis of

autoimmunity diseases.autoimmunity diseases.

CH2

C HO

CH2

C

O P

R2

O

Cardiolipin

O

OH

O

C R1OO

CH2

CH OH

CH2 CH2

CH O

CH2

C

OP

R3

O

O

OH

O

CR4 O

O

B-SphingophospholipidsB-Sphingophospholipids1-Sphingomyelins1-Sphingomyelins• Definition:Definition: Sphingomyelins are found in large Sphingomyelins are found in large

amounts in brain and nerves and in smaller amounts amounts in brain and nerves and in smaller amounts in lung, spleen, kidney, liver and bloodin lung, spleen, kidney, liver and blood.

• Structure:Structure: Sphingomyelins differ from lecithins and Sphingomyelins differ from lecithins and cephalins in that they contain sphingosine as the cephalins in that they contain sphingosine as the alcohol instead of glycerol, they contain two alcohol instead of glycerol, they contain two nitrogenous bases: sphingosine itself and choline. nitrogenous bases: sphingosine itself and choline.

• Thus, sphingomyelins contain sphingosine base, Thus, sphingomyelins contain sphingosine base, one long-chain fatty acid, choline and phosphoric one long-chain fatty acid, choline and phosphoric acid. acid.

• To the amino group of sphingosine the fatty acid is To the amino group of sphingosine the fatty acid is attached by an amide linkage.attached by an amide linkage.

• Ceramide This part of sphingomyelin in which This part of sphingomyelin in which the amino group of sphingosine is attached to the the amino group of sphingosine is attached to the fatty acid by an amide linkage. fatty acid by an amide linkage.

• Ceramides have been found in the free state in the Ceramides have been found in the free state in the spleen, liver and red cells. spleen, liver and red cells.

CH CH NH

CH2

CHCH(CH2)12CH3

OH

Sphingosine

C R1

O

O

P O

OH

O CH2 CH2 N

CH3

CH3

CH3

+

Choline

Fatty acid

Phosphate

Ceramide

Sphingomyelin

B-GlycolipidsB-Glycolipids• DefinitionDefinition: They are lipids that contain They are lipids that contain

carbohydrate residues with sphingosine as the carbohydrate residues with sphingosine as the alcohol and a very long-chain fatty acid (24 carbon alcohol and a very long-chain fatty acid (24 carbon series). series).

• They are present in cerebral tissue, therefore are They are present in cerebral tissue, therefore are

called called cerebrosidescerebrosides • ClassificationClassification: According to the number and According to the number and

nature of the carbohydrate residue(s) present in nature of the carbohydrate residue(s) present in the glycolipids the following arethe glycolipids the following are

1. Cerebrosides. They have one galactose They have one galactose molecule (galactosides).molecule (galactosides).

2. Sulfatides. They are cerebrosides with sulfate on They are cerebrosides with sulfate on the sugar (sulfated cerebrosides).the sugar (sulfated cerebrosides).

3. Gangliosides. They have several sugar and They have several sugar and sugaramine residues.sugaramine residues.

1-Cerebrosides:1-Cerebrosides:• Occurrence: They occur in myelin sheath of nerves and white

matter of the brain tissues and cellular membranes. They are important for nerve conductance.

• Structure: They contain sugar, usually -galactose and may be glucose or lactose, sphingosine and fatty acid, but no phosphoric

acid.

CH CH NH

CH 2

CHCH(CH 2)12CH 3

OH

Sphingosine

C R1

O

O

Psychosin

Fatty acid

Ceramide

Cerebroside

OOH

H HH

OHH

OH

CH 2OH

HGalactose

• TypesTypes: According to the type of fatty acid According to the type of fatty acid and carbohydrate present, there are 4 and carbohydrate present, there are 4 different types of cerebrosides isolated different types of cerebrosides isolated from the white matter of cerebrum and in from the white matter of cerebrum and in myelin sheaths of nerves. Rabbit myelin sheaths of nerves. Rabbit cerebrosides contain stearic acid.cerebrosides contain stearic acid.

1.1. KerasinKerasin contains lignoceric acid (24 contains lignoceric acid (24 carbons) and galactose.carbons) and galactose.

2.2. Cerebron (Phrenosin)Cerebron (Phrenosin) contains cerebronic contains cerebronic acid (2-hydroxylignoceric acid) and acid (2-hydroxylignoceric acid) and galactose.galactose.

3.3. NervonNervon contains nervonic acid (unsaturated contains nervonic acid (unsaturated lignoceric acid at C15) and galactose. lignoceric acid at C15) and galactose.

4.4. OxynervonOxynervon contains oxynervonic acid (2- contains oxynervonic acid (2-hydroxynervonic acid) and galactose. hydroxynervonic acid) and galactose.

2-Sulfatides2-Sulfatides:• They are sulfate esters of kerasin or phrenosin in They are sulfate esters of kerasin or phrenosin in

which the sulfate group is usually attached to the –which the sulfate group is usually attached to the –OH group of C3 or C6 of galactose. Sulfatides are OH group of C3 or C6 of galactose. Sulfatides are usually present in the brain, liver, muscles and usually present in the brain, liver, muscles and testes.testes.

CH CH NH

CH 2

CHCH 2(CH 2)12CH 3

OH

C R1

O

O

Sulfatides (sulfated cerebroside)

OOH

H HH

OHH

OSO3H

CH 2OH

H

3-Gangliosides:3-Gangliosides: • They are more complex glycolipids that occur in the They are more complex glycolipids that occur in the

gray matter of the brain, ganglion cells, and RBCs. gray matter of the brain, ganglion cells, and RBCs. They transfer biogenic amines across the cell They transfer biogenic amines across the cell membrane and act as a cell membrane receptor. membrane and act as a cell membrane receptor.

• GangliosidesGangliosides contain contain sialic acid (N-sialic acid (N-acetylneuraminicacetylneuraminic acid),acid), ceramide (sphingosine + ceramide (sphingosine + fatty acid of 18-24 carbon atom length), 3 molecules fatty acid of 18-24 carbon atom length), 3 molecules of hexoses (1 glucose + 2 galactose) and of hexoses (1 glucose + 2 galactose) and hexosamine. The most simple type of it the hexosamine. The most simple type of it the monosialoganglioside,. It works as a receptor for monosialoganglioside,. It works as a receptor for cholera toxin in the human intestine.cholera toxin in the human intestine.

Ceramide-Glucose-Galactose-N-acetylgalactosamine-Galactose

Monosialoganglioside

Sialic acid

C-LipoproteinsC-Lipoproteins• DefinitionDefinition: Lipoproteins are lipids combined with Lipoproteins are lipids combined with

proteins in the tissues. The lipid component is proteins in the tissues. The lipid component is phospholipid, cholesterol or triglycerides. The phospholipid, cholesterol or triglycerides. The holding bonds are secondary bonds.holding bonds are secondary bonds.

• They include:They include:1.1. Structural lipoproteinsStructural lipoproteins: These are widely distributed : These are widely distributed

in tissues being present in cellular and subcellular in tissues being present in cellular and subcellular membranes. In lung tissues acting as a surfactant in membranes. In lung tissues acting as a surfactant in a complex of a protein and lecithin. In the eye, a complex of a protein and lecithin. In the eye, rhodopsin of rods is a lipoprotein complex.rhodopsin of rods is a lipoprotein complex.

• Transport lipoproteinsTransport lipoproteins: : • These are the forms present in blood plasma. They These are the forms present in blood plasma. They

are composed of a protein called are composed of a protein called apolipoprotein apolipoprotein and and different types of lipids. (Cholesterol, cholesterol different types of lipids. (Cholesterol, cholesterol esters, phospholipids and triglycerides). As the lipid esters, phospholipids and triglycerides). As the lipid content increases, the density of plasma content increases, the density of plasma lipoproteins decreaseslipoproteins decreases

• Plasma lipoproteins can be separated by two Plasma lipoproteins can be separated by two methodsmethods:

1.1. Ultra-centrifugationUltra-centrifugation: Using the rate of floatation in : Using the rate of floatation in sodium chloride solution leading to their sequential sodium chloride solution leading to their sequential separation into separation into chylomicronschylomicrons, very low density , very low density lipoproteins (lipoproteins (VLDL or pre-VLDL or pre--lipoproteins-lipoproteins), low ), low density lipoproteins (density lipoproteins (LDL or LDL or -lipoproteins-lipoproteins), high ), high density lipoproteins (density lipoproteins (HDL or HDL or -lipoproteins-lipoproteins) and ) and albumin-free fattyalbumin-free fatty acids complex. acids complex.

2.2. ElectrophoresisElectrophoresis:: is the migration of charged is the migration of charged particles in an electric field either to the anode or to particles in an electric field either to the anode or to the cathode. It sequentially separates the the cathode. It sequentially separates the lipoproteins into lipoproteins into chylomicronschylomicrons, , pre-pre--, -, -, and -, and --lipoprotein and lipoprotein and albumin-free fattyalbumin-free fatty acids complex acids complex.

Polar lipids(phospholipids)

Nonpolar lipids(cholesterol and its esters

and triacylglycerols)Structure of a plasma lipoprotein complex

Polar apolipoproteins

a) Chylomicronsa) Chylomicrons: They have the largest diameter They have the largest diameter and the least density. They contain and the least density. They contain 1-2% protein1-2% protein only only and and 98-99% fat98-99% fat. The main lipid fraction is . The main lipid fraction is triglycerides absorbed from the intestine and they triglycerides absorbed from the intestine and they contain contain small amountssmall amounts of the absorbed cholesterol of the absorbed cholesterol and phospholipids.and phospholipids.

b) Very low-density lipoproteins (VLDL) or pre-b) Very low-density lipoproteins (VLDL) or pre--lipoproteins-lipoproteins: Their diameter is smaller than Their diameter is smaller than chylomicrons. They contain about chylomicrons. They contain about 7-10% protein7-10% protein and and 90-93% lipid90-93% lipid. The lipid content is mainly triglycerides . The lipid content is mainly triglycerides formed in the liver. They contain phospholipid and formed in the liver. They contain phospholipid and cholesterol cholesterol more thanmore than chylomicrons. chylomicrons.

c) Low-density lipoproteins (LDL) or ) Low-density lipoproteins (LDL) or --lipoproteinslipoproteins: They contain They contain 10-20% proteins10-20% proteins in the in the form of apolipoprotein B. Their form of apolipoprotein B. Their lipid content varies lipid content varies from 80-90%.from 80-90%. They contain about 60% of total blood They contain about 60% of total blood cholesterol and 40% of total blood phospholipids. As cholesterol and 40% of total blood phospholipids. As their percentage increases, the liability to their percentage increases, the liability to atherosclerosis increases.atherosclerosis increases.

d) High-density lipoproteins (HDL) or d) High-density lipoproteins (HDL) or --LipoproteinsLipoproteins: They contain They contain 35-55% proteins35-55% proteins in the form of apolipoprotein A. They contain in the form of apolipoprotein A. They contain 45-65% lipids45-65% lipids formed of cholesterol ( formed of cholesterol (40% of40% of total blood contenttotal blood content) and phospholipids () and phospholipids (60%60% of total blood contentof total blood content). They act as ). They act as cholesterol cholesterol scavengersscavengers, as their percentage , as their percentage increases, the liability to atherosclerosis increases, the liability to atherosclerosis decreases. They are higher in females than in decreases. They are higher in females than in males. Due to their high protein content they males. Due to their high protein content they possess the highest density.possess the highest density.

e) Albumin-free fatty acids complex:e) Albumin-free fatty acids complex: It is a It is a proteolipid complex with proteolipid complex with 99% protein99% protein content content associated with long-chain free fatty acids associated with long-chain free fatty acids for transporting them.for transporting them.

Cholesterol:Cholesterol:• Importance:Importance: - - • It is the most important sterol in animal tissues as It is the most important sterol in animal tissues as

free alcoholfree alcohol or in an esterified form ( or in an esterified form (with linoleicwith linoleic, , oleic, palmitic acids or other fatty acidsoleic, palmitic acids or other fatty acids).).

• Steroid hormones, bile salts and vitamin D are Steroid hormones, bile salts and vitamin D are derivatives from it. derivatives from it.

• Tissues contain different amounts of it that serve a Tissues contain different amounts of it that serve a structural and metabolic role, e.g., structural and metabolic role, e.g., adrenal cortexadrenal cortex content is 10%,content is 10%, whereas, whereas, brain is 2%,brain is 2%, others 0.2- others 0.2-0.3%.0.3%.

• SourceSource:: - It is synthesized in the body from acetyl-It is synthesized in the body from acetyl-CoA (1gm/day, cholesterol does not exist in plants) CoA (1gm/day, cholesterol does not exist in plants) and is also taken in the diet (and is also taken in the diet (0.3 gm/day as in, butter, 0.3 gm/day as in, butter, milk, egg yolk, brain, meat and animal fat).milk, egg yolk, brain, meat and animal fat).

Physical propeties:Physical propeties:It has a hydroxyl group on C3, a double bond between C5 and C6, 8 asymmetric carbon atoms and a side chain of 8 carbon atoms.

• It is found in all animal cells, corpus luteum and adrenal cortex, human brain (17% of the solids).

• In the blood (the total cholesterol amounts about 200 mg/dL of which 2/3 is esterified, chiefly to unsaturated fatty acids while the remainder occurs as the free cholesterol.

CH 3

CH 3

HO

CH 3

CH 3

CH 3

Cholesterol

• Chemical propertiesChemical properties Intestinal bacteria reduce Intestinal bacteria reduce cholesterol into cholesterol into coprosterol and dihydrocholesterolcoprosterol and dihydrocholesterol. .

• - It is also oxidized into- It is also oxidized into 7-Dehydrocholesterol 7-Dehydrocholesterol and and further unsaturated cholesterol with a second further unsaturated cholesterol with a second double bond between double bond between C7 and C8.C7 and C8. When the skin is When the skin is irradiated with ultraviolet light 7-dehydrocholesterol irradiated with ultraviolet light 7-dehydrocholesterol is converted to vitamin is converted to vitamin D3.D3. This explains the value This explains the value of sun light in preventing of sun light in preventing ricketsrickets..

CH 3

CH 3

HO

CH 3

CH 3

CH 3

Coprosterol,in feces

H

CH 3

CH 3

HO

CH 3

CH 3

CH 3

Dihydrocholesterol,in blood and other tissues

H

• ErgosterolErgosterol differs from 7-dehydrocholesterol in differs from 7-dehydrocholesterol in the side chain. Ergosterol is converted to vitamin D2 the side chain. Ergosterol is converted to vitamin D2 by irradiation with UV Ergosterol and 7- by irradiation with UV Ergosterol and 7- dehydrocholesterol are called Pro-vitamins D or dehydrocholesterol are called Pro-vitamins D or precursors of vitamin D. precursors of vitamin D.

• - It was first isolated from ergot, a fungus then from - It was first isolated from ergot, a fungus then from yeast. Ergosterol is less stable than cholesterol yeast. Ergosterol is less stable than cholesterol ((because of having 3 double bondsbecause of having 3 double bonds).).

CH 3

CH 3

HO

CH 3

CH 3

CH 3

7-dehydrocholesterol

CH 3

CH 3

HO

CH 3CH 3

CH 3

Ergosterol

CH 3

SteroidsSteroids• Steroids constitute an important class of Steroids constitute an important class of

biological compounds.biological compounds.• Steroids are usually found in association Steroids are usually found in association

with fat. They can be separated from fats with fat. They can be separated from fats after saponification since they occur in the after saponification since they occur in the unsaponifiable residue.unsaponifiable residue.

• They are They are derivatives of cholesterolderivatives of cholesterol that is that is formed of steroid ring or nucleus.formed of steroid ring or nucleus.

• Biologically important groups of substances, which Biologically important groups of substances, which contain this ring, are:contain this ring, are:

1.1. Sterols.Sterols.2.2. Adrenal cortical hormones.Adrenal cortical hormones.3.3. Male and female sex hormones.Male and female sex hormones.4.4. Vitamin D group.Vitamin D group.5.5. Bile acids.Bile acids.6.6. Cardiac glycosides.Cardiac glycosides.

• General consideration about naturally occurring steroidsGeneral consideration about naturally occurring steroids: A typical member of this group A typical member of this group is cholesterolis cholesterol. Certain facts . Certain facts

have to be considered when drawing steroid formulahave to be considered when drawing steroid formula:1) There is always oxygen in the form of 1) There is always oxygen in the form of hydroxyl or ketone on C3hydroxyl or ketone on C3..2) Rings 2) Rings C and D are saturatedC and D are saturated (stable). (stable).3) Methyl groups at 3) Methyl groups at C18 C19C18 C19. In case of vitamin D, . In case of vitamin D, the CH3the CH3 group group

at C19 becomes a methylene group (=CH2) and the ring B is at C19 becomes a methylene group (=CH2) and the ring B is opened, whereas, opened, whereas, this methyl group is absent in female sex this methyl group is absent in female sex hormones (estrogens).hormones (estrogens).

4) In estrogens (female sex hormones) ring A is aromatic and 4) In estrogens (female sex hormones) ring A is aromatic and there is there is no methyl group on C10.no methyl group on C10.

CH 3

CH 3

HO

Steroid ring

12

3 45

6 7

89

10

11

12

13

14 15

1617

18

19

A B

C D

• Bile acidsBile acids:

• They are produced from oxidation of cholesterol in They are produced from oxidation of cholesterol in the liver producing the liver producing cholic and chenodeoxycholic cholic and chenodeoxycholic acidsacids that are conjugated with that are conjugated with glycine or taurineglycine or taurine to to produce produce glycocholic,glycocholic, glycochenodeoxycholic, glycochenodeoxycholic, taurocholictaurocholic and taurochenodeoxycholic acids. They and taurochenodeoxycholic acids. They react with sodium or potassium to produce react with sodium or potassium to produce sodiumsodium or or potassium bile saltspotassium bile salts..

• Their function is as followsTheir function is as follows:

1.1. Emulsification of lipids during digestion.Emulsification of lipids during digestion.2.2. Help in digestion of the other foodstuffs.Help in digestion of the other foodstuffs.3.3. Activation of pancreatic lipase.Activation of pancreatic lipase.4.4. Help digestion and absorption of fat-soluble Help digestion and absorption of fat-soluble

vitamins.vitamins.5.5. Solubilizing cholesterol in bile and prevent gall Solubilizing cholesterol in bile and prevent gall

stone formation.stone formation.6.6. Choleretic action (stimulate their own secretion).Choleretic action (stimulate their own secretion).7.7. Intestinal antiseptic that prevent putrefactionIntestinal antiseptic that prevent putrefaction

CH 3

CH 3

HO

CH 3

C

Sodium-tauro orglyco-cholate

CH 3

CH 3

HO

CH 3

C

Sodium-tauro orglyco-chenodeoxycholate

OH

OH OH

O O

R1 or R2 R1 or R2

(CH 2)2 SO3-Na+H2NCH 2 COO -Na+H2N

Sodium taurateSodium glycateR1 R2