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Chemistry of LipidsChemistry 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 LipidsClassification of Lipids
1. Simple lipids (Fats & Waxes)
2. Complex (compound or conjugated lipids)
3. Derived Lipids4. Lipid-associating
substances
But first, But first,
Fatty alcoholsFatty alcohols (glycerol & (glycerol & sphingosine)sphingosine)
Glycerol: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 Glycerol:Uses of Glycerol:1. 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.
4. explosives manufacturing.5. treatment of glaucoma (increased
intraocular pressure)due to its ability to dehydrate the tissue from its water content.
Sphingosine:Sphingosine:- the alcohol(monohydric) present in
sphingolipids. - 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 AcidsFatty AcidsDefinitionDefinition: aliphatic mono-carboxylic acids that
are mostly obtained from the hydrolysis of natural fats and oils.
the general formula R-(CH2)n-COOH and mostly have straight chain (a few
exceptions have branched and heterocyclic chains). "n" is mostly an even number of carbon atoms (2-34)
Classification of Classification of FATTY ACIDS FATTY ACIDS According to presence or absence of According to presence or absence of double bonds they are classified intodouble bonds they are classified into::
>SatURATED FA>unsatURATED FA
1-Saturated Fatty Acids
no double bonds with 2-24 or more carbons. solid at RT except if they are short chained. may be even or odd numbered. molecular formula, CnH2n+1COOH.
Saturated Fatty acids could be: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 C).b-Short chain Saturated non volatile F.A.(7-10 C).
B-Long chain Saturated F.AB-Long chain Saturated F.A. (more than . (more than 10 carbon)10 carbon)
A-A- SATurated- short chain SATurated- short chain
Volatile Volatile short-chainshort-chain fatty fatty acids:acids:
liquid in nature and contain liquid in nature and contain 1-6 C1-6 C water-solublewater-solublevolatile at room temperaturevolatile at room temperature e.g., acetic, butyric,& caproic acids.e.g., acetic, butyric,& 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.
A- Saturated- Short chain
Non-volatile Non-volatile short-chain short-chain fatty acidsfatty acids:
solids at room temperaturesolids at room temperaturecontain contain 7-107-10 carbons. carbons.water-solublewater-soluble non-volatile at RTnon-volatile at RTinclude caprylic and capric F.A.include 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-B- Saturated- LONG CHAIN Saturated- LONG CHAIN
Long-chain fatty acids: >10 carbon atoms. in hydrogenated oils, animal fats,
butter and coconut and palm oils. non-volatilewater-insoluble E.g. palmitic, stearic, & lignoceric
F.A. palmitic(16C) CHpalmitic(16C) CH33-(CH-(CH22))1414-COOH-COOHstearic (18 C ) CHstearic (18 C ) CH33-(CH-(CH22))1616-COOH -COOH lignoceric (24C ) CHlignoceric (24C ) CH33-(CH-(CH22))2222-COOH -COOH
2-Unsaturated Fatty Acids
- contain double bond- TYPES:A. monounsaturated they contain one double bond .(CnH2n-1 COOH) B. polyunsaturated they contain more the one double bond
(CnH2n-# COOH).
A-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
B-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.
Symptoms: Symptoms: poor growth and health with susceptibility to infections, dermatitis, decreased capacity to reproduce, impaired transport of lipids, fatty liver, and lowered resistance to stress.
FunctionFunction of Essential Fatty of Essential Fatty Acids: 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.
POLYUnsat FA:
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
POLYUnsat FA:
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
POLYUnsat FA:
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
Classification of LipidsClassification of Lipids
1. Simple lipids (Fats & Waxes)
2. Compound or conjugated lipids
3. Derived Lipids4. Lipid-associating
substances
Classification of LipidsClassification of Lipids
1. Simple lipids (Fats & Waxes)
Simple LipidsSimple LipidsA-Neutral Fats and oilsA-Neutral Fats and oils (Triglycerides)(Triglycerides)
Definition:Definition:Neutral- uncharged due to absence of Neutral- uncharged due to absence of
ionizable groups in it. ionizable groups in it. most abundant lipids in nature. most abundant lipids in nature. constitute about 98% of the lipids of constitute about 98% of the lipids of
adipose tissue, 30% of plasma or liver adipose tissue, 30% of plasma or liver lipids, less than 10% of erythrocyte lipids, less than 10% of erythrocyte lipids.lipids.
They are esters of glycerol with various They are esters of glycerol with various fatty acids. Since the 3 hydroxyl groups of fatty 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 Esterification of glycerol with one molecule of fatty acid gives molecule of fatty acid gives monoglyceridemonoglyceride, and that with 2 , and that with 2 molecules gives 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 triglycerides1-Simple triglycerides1-Simple triglycerides: : If the three fatty If the three fatty
acids connected to glycerol are of the acids connected to glycerol are of the same type the triglyceride is called same type the triglyceride is called simple triglyceride, e.g., tripalmitin.simple triglyceride, e.g., tripalmitin.
2-Mixed triglycerides2-Mixed triglycerides: : if they are of if they are of different types, it is called mixed different types, it is called mixed triglycerides, e.g., stearo-diolein and triglycerides, e.g., stearo-diolein and palmito-oleo-stearin.palmito-oleo-stearin.
> > Natural fats Natural fats are mixtures of mixed 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 animal The commonest fatty acids in animal fats are fats are palmitic, stearic and oleic palmitic, stearic and oleic acids. 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 are fats are solids.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.
PhysicalPhysical properties of fat and properties of fat and oils: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 (one) 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 Chemical Properties of fats Properties of fats and oilsand oils:
1-Hydrolysis:1-Hydrolysis:hydrolyzed into their constituents (hydrolyzed into their constituents (fatty acids fatty acids
and glycerol)and glycerol) by heated steam, acid, alkali or by heated steam, acid, alkali or enzyme (e.g., lipase of pancreas). enzyme (e.g., lipase of pancreas).
- During their enzymatic and acid hydrolysis - During their enzymatic and acid hydrolysis glycerol and free fatty acids are produced. glycerol 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 produces glycerol Alkaline hydrolysis produces glycerol
and salts of fatty acids (and salts of fatty acids (soapssoaps).).Soaps cause emulsification of oily Soaps cause emulsification of oily
material this help easy washing of the material this help easy washing of the fatty materialsfatty 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-HalogenationNeutral fats containing unsaturated fatty Neutral fats containing unsaturated fatty
acids have the ability of adding halogens acids have the ability of adding halogens (e.g., hydrogen or hydrogenation and iodine (e.g., hydrogen or hydrogenation and iodine or iodination) at the double bonds.or iodination) at the double bonds.
very important property to determine the 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 4-Hydrogenation or hardening of oilshardening of oils:
It is a type of addition reactions accepting It is a type of addition reactions accepting hydrogen at the double bonds of hydrogen at the double bonds of unsaturated fatty acids.unsaturated 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 manufacturingmargarine manufacturing), e.g., change of ), e.g., change of oleic acid of fats (liquid) into stearic acid oleic acid of fats (liquid) into stearic acid (solid).(solid).
It is advisable not to saturate all double It is advisable not to saturate all double bonds; otherwise margarine produced will bonds; otherwise margarine produced will be very hard, of very low biological value be very hard, of very low biological value and difficult to digest.and difficult to digest.
Oils(liquid)
(with unsaturated fatty acids, e.g., oleic)
Hard fat(margarine, solid)(with saturated
fatty acids, e.g., stearic)
Hydrogen, high pressure, nickel
Advantages for hydrogenatedAdvantages for hydrogenated oil or fat are as followsoil 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 It is digestible and utilizable as normal animal
fats and oils.fats 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 It is easily stored and transported and less
liable to rancidity.liable to rancidity.
Disadvantages of hydrogenatedDisadvantages of hydrogenated fats include lack of fat-soluble vitamins (A, D, E fats include lack of fat-soluble vitamins (A, D, E
and K) and essential fatty acidsand K) and essential fatty acids
5-Oxidation (Rancidity)5-Oxidation (Rancidity)
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
= RANCID
RancidityRancidityDefinition:Definition:physico-chemical change physico-chemical change development of development of unpleasant odor or unpleasant odor or
taste or abnormal colortaste or abnormal color particularly particularly on agingon aging
exposure to atmospheric oxygen, exposure to atmospheric oxygen, light, moisture, bacterial or fungal light, moisture, bacterial or fungal contamination and/or heat. contamination and/or heat.
Saturated fats resist rancidity Saturated fats resist rancidity more than unsaturated fats that more than unsaturated fats that have unsaturated double bonds.have unsaturated double bonds.
Types and causes of RancidityTypes and causes of Rancidity:1.1. Hydrolytic rancidityHydrolytic rancidity2.2. Oxidative rancidityOxidative rancidity3.3. Ketonic rancidityKetonic rancidity
1-Hydrolytic rancidity1-Hydrolytic rancidity: from slight hydrolysis of the fat by from slight hydrolysis of the fat by
lipaselipase bacterial contamination leading to bacterial contamination leading to
the the liberation of free fatty acids and liberation of free fatty acids and glycerol glycerol at high temp and moisture. at high temp and moisture.
Volatile short-chain fatty acids Volatile short-chain fatty acids have unpleasant odor.have 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: oxidation of fat or oil oxidation of fat or oil by exposure to oxygen, light and/or by exposure to oxygen, light and/or
heat producing peroxide derivatives heat producing peroxide derivatives e.g., e.g., peroxides, aldehydes, ketones peroxides, aldehydes, ketones
and dicarboxylic acids that are toxic and dicarboxylic acids that are toxic and have bad odor.and have bad odor.
due to oxidative addition of oxygen at due to oxidative addition of oxygen at the unsaturated double bond of the unsaturated double bond of unsaturated fatty acid of oils.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: due to the contamination with certain due to the contamination with certain
fungi such as fungi such as Aspergillus niger Aspergillus niger on on fats such as fats such as coconut oilcoconut 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 Moisture accelerates ketonic rancidity.rancidity.
Prevention of rancidityPrevention of rancidityAvoidance 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 keeping fats or oils in well-closed By keeping fats or oils in well-closed containers in cold, dark and dry place (i.e., containers in cold, dark and dry place (i.e., good storage conditions).good storage conditions).
Removal of catalysts such as lead and Removal of catalysts such as lead and copper that catalyze rancidity.copper that catalyze rancidity.
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 The products of rancidity are toxic,toxic,
i.e., causes i.e., causes food poisoning and food poisoning and cancercancer..
2.2. Rancidity destroys the fat-soluble Rancidity destroys the fat-soluble vitamins (vitamins (vitamins A, D, K and Evitamins A, D, K and E).).
3.3. Rancidity destroys the Rancidity destroys the polyunsaturated essential fatty polyunsaturated essential fatty acidsacids..
4.4. Rancidity causes Rancidity causes economical loss economical loss because rancid fat is inedible.because rancid fat is inedible.
B-WaxesB-WaxesDefinitionDefinition: 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. esterified to long-chain fatty acids. Examples of these alcohols are Examples of these alcohols are palmitoyl palmitoyl alcohol, cholesterol, vitamin A or D.alcohol, cholesterol, vitamin A or D.
Properties of waxesProperties of waxes: Waxes are : Waxes are insoluble in water, but soluble in fat insoluble in water, but soluble in fat solvents and are negative for acrolein solvents and are negative for acrolein test. test.
Waxes are not easily hydrolyzed as the Waxes are not easily hydrolyzed as the fats and are indigestible by lipases and fats and are indigestible by lipases and are very resistant to rancidity. are very 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.
C15H31 C OHO
+C30H61OH C15H31 C OO
C30H61
H2OPalmiticacid
Mericylalcohol
Mericylpalmitate
B-Wax-like compounds: Cholesterol estersCholesterol esters: Lanolin (or wool Lanolin (or wool
fat) is prepared from the wool-fat) is prepared from the wool-associated skin glands and is associated skin glands and is secreted by sebaceous glands of secreted by sebaceous glands of the skin. the skin.
It is very complex mixture, contains It is very complex mixture, contains both free and esterified cholesterol, both free and esterified cholesterol, e.g., cholesterol-palmitate and e.g., cholesterol-palmitate and other sterolsother sterols.
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 They are lipids that contain
additional substances, e.g., sulfur, additional substances, e.g., sulfur, phosphorus, amino group, phosphorus, amino group, carbohydrate, or proteins beside 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 classified into the following types according to the nature of the according to the nature of the additional group: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 compound lipids, which contain phosphoric acid group in their structureacid group in their structure. .
ImportanceImportance: 1.1.They are present in large amounts in the They are present in large amounts in the
liver and brain as well as blood. Every liver and brain as well as blood. Every animal and plant cell contains animal and plant cell contains phospholipids. phospholipids.
2.2.The membranes bounding cells and The membranes bounding cells and subcellular organelles are composed mainly subcellular organelles are composed mainly of phospholipids. Thus, the transfer of of phospholipids. Thus, the transfer of substances through these membranes is substances through these membranes is controlled by properties of phospholipids.controlled by properties of phospholipids.
3.3.They are important components of the They are important components of the lipoprotein coat essential for secretion and lipoprotein coat essential for secretion and transport of plasma lipoprotein complexes. transport of plasma lipoprotein complexes. Thus, they are lipotropic agents that Thus, they are lipotropic agents that prevent fatty liverprevent fatty liver..
4.4.Myelin sheath of nerves is rich with Myelin sheath of nerves is rich with phospholipids.phospholipids.
5-Important in digestion and 5-Important in digestion and absorption of neutral lipids and absorption of neutral lipids and excretion of cholesterol in the bile.excretion of cholesterol in the bile.
6-Important function in blood clotting 6-Important function in blood clotting and platelet aggregation.and platelet aggregation.
7-They provide lung alveoli with 7-They provide lung alveoli with surfactants that prevent its surfactants that prevent its irreversible collapseirreversible collapse..
8-Important role in signal transduction 8-Important role in signal transduction across the cell membrane.across the cell membrane.
9-Phospholipase A2 in snake venom 9-Phospholipase A2 in snake venom hydrolyses membrane hydrolyses membrane phospholipids into hemolytic phospholipids into hemolytic lysolecithin or lysocephalin.lysolecithin or lysocephalin.
10-They are source of polyunsaturated 10-They are source of polyunsaturated fatty acids for synthesis of fatty acids for synthesis of eicosanoids.eicosanoids.
Sources:Sources: They are found in all cells They are found in all cells (plant and animal), milk and egg-(plant and animal), milk and egg-yolk in the form of lecithins.yolk in the form of lecithins.
StructureStructure: phospholipids are composed phospholipids are composed of: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 classified into 2 groups according to the type of the the type of the alcoholalcohol present into present into two types:two types:
A-A-GlycerophospholipidsGlycerophospholipids: They are They are regarded as derivatives of phosphatidic regarded as derivatives of phosphatidic acids that are the simplest type of acids that are the simplest type of phospholipids and include: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 They are metabolic
intermediates in synthesis of triglycerides intermediates in synthesis of triglycerides and glycerophospholipids in the body and and glycerophospholipids in the body and may have function as a may have function as a second messengersecond messenger. . They exist in two forms according to the They exist in two forms according to the position of the phosphateposition 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 glycerophospholipids that contain choline as a base beside phosphatidic choline as a base beside phosphatidic acid. They exist in 2 forms acid. They exist in 2 forms - and - and --lecithins. Lecithins are a common cell lecithins. Lecithins are a common cell constituent obtained from brain (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 Glycerol is connected at C2 or C3 with a polyunsaturated fatty acid, at C3 with a polyunsaturated fatty acid, at C1 with a saturated fatty acid, at C3 or C1 with a saturated fatty acid, at C3 or C2 by phosphate to which the choline C2 by phosphate to which the choline base is connected. The common fatty base is connected. The common fatty acids in lecithins are stearic, palmitic, acids in lecithins are stearic, palmitic, oleic, linoleic, linolenic, clupandonic or oleic, linoleic, linolenic, clupandonic or arachidonic acids.arachidonic acids.
LysolecithinLysolecithin causes hemolysis of RBCs. This causes hemolysis of RBCs. This partially explains toxic effect of snake partially explains toxic effect of snake venom,. The venom contains venom,. The venom contains lecithinaselecithinase, , which hydrolyzes the polyunsaturated which hydrolyzes the polyunsaturated fatty converting lecithin into lysolecithin. fatty converting lecithin into lysolecithin. Lysolecithins are intermediates in 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, Is a complex of dipalmitoyl-lecithin,
sphingomyelin and a group of apoproteins sphingomyelin and a group of apoproteins called apoprotein A, B, C, and D. called apoprotein A, B, C, and D.
It is produced by type II alveolar cells and It is produced by type II alveolar cells and is anchored to the alveolar surface of type is anchored to the alveolar surface of type II and I cells. II and I cells.
It lowers alveolar surface tension and It lowers alveolar surface tension and improves gas exchange besides activating improves gas exchange besides activating macrophages to kill pathogens. macrophages to kill pathogens.
In premature babies, this surfactant is In premature babies, this surfactant is deficient and they suffer from deficient and they suffer from respiratory respiratory distress syndromedistress syndrome. .
Glucocorticoids increase the synthesis of Glucocorticoids increase the synthesis of the surfactant complex and promote the surfactant complex and promote differentiation of lung cells.differentiation of 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 tissues and are isolated from the brain (brain (Kephale = head).Kephale = head).
StructureStructure: Cephalins resemble : Cephalins resemble lecithins in structure except that lecithins in structure except that choline is replaced by ethanolamine, choline is replaced by ethanolamine, serine or threonine amino acids.serine or threonine amino acids.
Certain cephalins are constituents of the Certain cephalins are constituents of the complex mixture of phospholipids, complex mixture of phospholipids, cholesterol and fat that constitute the lipid cholesterol and fat that constitute the lipid component of the lipoprotein component of the lipoprotein ““thromboplastinthromboplastin” which accelerates the ” which accelerates the clotting of blood by activation of clotting of blood by activation of prothrombin to thrombin in presence of prothrombin to thrombin in presence of calcium ionscalcium 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 Plasmalogens are found in
the cell membrane phospholipids the cell membrane phospholipids fraction of brain and muscle (10% of fraction of brain and muscle (10% of it is plasmalogens), liver, semen and it is plasmalogens), liver, semen and eggs.eggs.
StructureStructure: Plasmalogens resemble Plasmalogens resemble lecithins and cephalins in structure lecithins and cephalins in structure but differ in the presence of but differ in the presence of ,,--unsaturated fatty alcoholunsaturated fatty alcohol rather than rather than a fatty acid at C1 of the glycerol a fatty acid at C1 of the glycerol connected by ether bond. connected by ether bond.
At C2 there is an unsaturated long-At C2 there is an unsaturated long-chain fatty acid, however, it may be a chain fatty acid, however, it may be a very short-chain fatty acid very short-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 They are similar to lecithins or
cephalins but they have the cyclic sugar cephalins but they have the cyclic sugar alcohol, alcohol, inositol inositol as the base. They are as the base. They are formed of glycerol, one saturated fatty acid, formed of glycerol, one saturated fatty acid, one unsaturated fatty acid, phosphoric acid one unsaturated fatty acid, phosphoric acid and inositoland 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 Phosphatidyl inositol is a major
component of cell membrane component of cell membrane phospholipids particularly at the phospholipids particularly at the inner leaflet of it. inner leaflet of it.
They play a major role as second They play a major role as second messengers during signal messengers during signal transduction for certain hormone.. transduction for 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 both act to liberate calcium from its intracellular stores calcium from its intracellular stores to mediate the hormone effects.to mediate the hormone effects.
6-Cardiolipins:6-Cardiolipins:DefinitionDefinition: They are diphosphatidyl-They are diphosphatidyl-
glycerol. They are found in the inner glycerol. They are found in the inner membrane of mitochondria initially isolated membrane of mitochondria initially isolated from heart muscle (cardio). It is formed of 3 from heart muscle (cardio). It is formed of 3 molecules of glycerol, 4 fatty acids and 2 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-SphingomyelinsDefinition:Definition: Sphingomyelins are found in Sphingomyelins are found in
large amounts in brain and nerves and in large amounts in brain and nerves and in smaller amounts in lung, spleen, kidney, smaller amounts in lung, spleen, kidney, liver and bloodliver and blood.
Structure:Structure: Sphingomyelins differ from Sphingomyelins differ from lecithins and cephalins in that they contain lecithins and cephalins in that they contain sphingosine as the alcohol instead of sphingosine as the alcohol instead of glycerol, they contain two nitrogenous glycerol, they contain two nitrogenous bases: sphingosine itself and choline. bases: sphingosine itself and choline.
Thus, sphingomyelins contain sphingosine Thus, sphingomyelins contain sphingosine base, one long-chain fatty acid, choline and base, one long-chain fatty acid, choline and phosphoric acid. phosphoric acid.
To the amino group of sphingosine the fatty To the amino group of sphingosine the fatty acid is attached by an amide linkage.acid is attached by an amide linkage.
Ceramide This part of sphingomyelin in This part of sphingomyelin in which the amino group of sphingosine is which the amino group of sphingosine is attached to the fatty acid by an amide attached to the fatty acid by an amide linkage. linkage.
Ceramides have been found in the free Ceramides have been found in the free state in the spleen, liver and red cells. state in the 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 carbohydrate residues with sphingosine as the alcohol and a very long-chain fatty as the alcohol and a very long-chain fatty acid (24 carbon series). acid (24 carbon series).
They are present in cerebral tissue, They are present in cerebral tissue, therefore are called therefore are called cerebrosidescerebrosides
ClassificationClassification: According to the number According to the number and nature of the carbohydrate residue(s) and nature of the carbohydrate residue(s) present in the glycolipids the following present in the glycolipids the following areare
1. Cerebrosides. They have one galactose They have one galactose molecule (galactosides).molecule (galactosides).
2. Sulfatides. They are cerebrosides with They are cerebrosides with sulfate on the sugar (sulfated sulfate on the sugar (sulfated cerebrosides).cerebrosides).
3. Gangliosides. They have several sugar They have several sugar and sugaramine residues.and 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
3-Gangliosides:3-Gangliosides: They are more complex glycolipids that They are more complex glycolipids that
occur in the gray matter of the brain, occur in the gray matter of the brain, ganglion cells, and RBCs. They transfer ganglion cells, and RBCs. They transfer biogenic amines across the cell membrane biogenic amines across the cell membrane and act as a cell membrane receptor. and act as a cell membrane receptor.
GangliosidesGangliosides contain contain sialic acid (N-sialic acid (N-acetylneuraminicacetylneuraminic acid),acid), ceramide ceramide (sphingosine + fatty acid of 18-24 carbon (sphingosine + fatty acid of 18-24 carbon atom length), 3 molecules of hexoses (1 atom length), 3 molecules of hexoses (1 glucose + 2 galactose) and hexosamine. The glucose + 2 galactose) and hexosamine. The most simple type of it the most simple type of it the monosialoganglioside,. It works as a monosialoganglioside,. It works as a receptor for cholera toxin in the human receptor for cholera toxin in the human intestine.intestine.Ceramide-Glucose-Galactose-N-acetylgalactosamine-Galactose
Monosialoganglioside
Sialic acid
C-LipoproteinsC-Lipoproteins DefinitionDefinition: Lipoproteins are lipids combined Lipoproteins are lipids combined
with proteins in the tissues. The lipid with proteins in the tissues. The lipid component is phospholipid, cholesterol or component is phospholipid, cholesterol or triglycerides. The holding bonds are triglycerides. The holding bonds are secondary bonds.secondary bonds.
They include:They include:1.1. Structural lipoproteinsStructural lipoproteins: These are widely : These are widely
distributed in tissues being present in distributed in tissues being present in cellular and subcellular membranes. In lung cellular and subcellular membranes. In lung tissues acting as a surfactant in a complex tissues acting as a surfactant in a complex of a protein and lecithin. In the eye, 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 These are the forms present in blood
plasma. They are composed of a protein plasma. They are composed of a protein called called apolipoprotein apolipoprotein and different types of and different types of lipids. (Cholesterol, cholesterol esters, lipids. (Cholesterol, cholesterol esters, phospholipids and triglycerides). As the phospholipids and triglycerides). As the lipid content increases, the density of lipid content increases, the density of plasma lipoproteins decreasesplasma lipoproteins decreases
Plasma lipoproteins can be separated by Plasma lipoproteins can be separated by two methodstwo methods:
1.1. Ultra-centrifugationUltra-centrifugation: Using the rate of : Using the rate of floatation in sodium chloride solution floatation in sodium chloride solution leading to their sequential separation into leading to their sequential separation into chylomicronschylomicrons, very low density , very low density lipoproteins (lipoproteins (VLDL or pre-VLDL or pre--lipoproteins-lipoproteins), ), low density lipoproteins (low density lipoproteins (LDL or LDL or --lipoproteinslipoproteins), high density lipoproteins ), high density lipoproteins ((HDL or HDL or -lipoproteins-lipoproteins) and ) and albumin-free albumin-free fattyfatty acids complex. acids complex.
2.2. ElectrophoresisElectrophoresis:: is the migration of is the migration of charged particles in an electric field either charged particles in an electric field either to the anode or to the cathode. It to the anode or to the cathode. It sequentially separates the lipoproteins sequentially separates the lipoproteins into into chylomicronschylomicrons, , pre-pre--, -, -, and -, and --lipoprotein and lipoprotein and albumin-free fattyalbumin-free fatty acids acids complexcomplex.
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 They have the largest diameter and the least density. They contain diameter and the least density. They contain 1-1-2% protein2% protein only and only and 98-99% fat98-99% fat. The main lipid . The main lipid fraction is triglycerides absorbed from the fraction is triglycerides absorbed from the intestine and they contain intestine and they contain small amountssmall amounts of the of the absorbed cholesterol and phospholipids.absorbed cholesterol and phospholipids.
b) Very low-density lipoproteins (VLDL) or b) Very low-density lipoproteins (VLDL) or pre-pre--lipoproteins-lipoproteins: Their diameter is smaller Their diameter is smaller than chylomicrons. They contain about than chylomicrons. They contain about 7-10% 7-10% proteinprotein and and 90-93% lipid90-93% lipid. The lipid content is . The lipid content is mainly triglycerides formed in the liver. They mainly triglycerides formed in the liver. They contain phospholipid and cholesterol contain phospholipid and 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 in the form of apolipoprotein B. Their the form of apolipoprotein B. Their lipid lipid content varies from 80-90%.content varies from 80-90%. They contain about They contain about 60% of total blood cholesterol and 40% of total 60% of total blood cholesterol and 40% of total blood phospholipids. As their percentage blood phospholipids. As their percentage increases, the liability to atherosclerosis increases, the liability to atherosclerosis increases.increases.
d) High-density lipoproteins (HDL) or d) High-density lipoproteins (HDL) or --LipoproteinsLipoproteins: They contain They contain 35-55% 35-55% proteinsproteins in the form of apolipoprotein A. in the form of apolipoprotein A. They contain They contain 45-65% lipids45-65% lipids formed of formed of cholesterol (cholesterol (40% of40% of total blood contenttotal blood content) ) and phospholipids (and phospholipids (60%60% of total blood of total blood contentcontent). They act as cholesterol ). They act as cholesterol scavengersscavengers, as their percentage , as their percentage increases, the liability to atherosclerosis increases, the liability to atherosclerosis decreases. They are higher in females decreases. They are higher in females than in males. Due to their high protein than in males. Due to their high protein content they possess the highest content they possess the highest density.density.
e) Albumin-free fatty acids complex:e) Albumin-free fatty acids complex: It is It is a proteolipid complex with a proteolipid complex with 99% protein99% protein content associated with long-chain free content associated with long-chain free fatty acids for transporting them.fatty acids for transporting them.
Cholesterol:Cholesterol:Importance:Importance: - - It is the most important sterol in animal It is the most important sterol in animal
tissues as tissues as free alcoholfree alcohol or in an esterified or in an esterified form (form (with linoleicwith linoleic, , oleic, palmitic acids or oleic, palmitic acids or other fatty acidsother fatty acids).).
Steroid hormones, bile salts and vitamin D Steroid hormones, bile salts and vitamin D are derivatives from it. are derivatives from it.
Tissues contain different amounts of it that Tissues contain different amounts of it that serve a structural and metabolic role, e.g., serve a structural and metabolic role, e.g., adrenal cortexadrenal cortex content is 10%,content is 10%, whereas, whereas, brain is 2%,brain is 2%, others 0.2-0.3%. others 0.2-0.3%.
SourceSource:: - It is synthesized in the body from It is synthesized in the body from acetyl-CoA (1gm/day, cholesterol does not acetyl-CoA (1gm/day, cholesterol does not exist in plants) and is also taken in the diet exist in plants) and is also taken in the diet ((0.3 gm/day as in, butter, milk, egg yolk, 0.3 gm/day as in, butter, milk, egg yolk, brain, meat and animal fat).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 Intestinal bacteria reduce cholesterol into reduce cholesterol into coprosterol and coprosterol and dihydrocholesteroldihydrocholesterol. .
- It is also oxidized into- It is also oxidized into 7- 7-DehydrocholesterolDehydrocholesterol and further unsaturated and further unsaturated cholesterol with a second double bond cholesterol with a second double bond between between C7 and C8.C7 and C8. When the skin is When the skin is irradiated with ultraviolet light 7-irradiated with ultraviolet light 7-dehydrocholesterol is converted to vitamin dehydrocholesterol is converted to vitamin D3.D3. This explains the value of sun light in This explains the value of sun light in preventing 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-differs from 7-dehydrocholesterol in the side chain. dehydrocholesterol in the side chain. Ergosterol is converted to vitamin D2 by Ergosterol is converted to vitamin D2 by irradiation with UV Ergosterol and 7- irradiation with UV Ergosterol and 7- dehydrocholesterol are called Pro-vitamins dehydrocholesterol are called Pro-vitamins D or precursors of vitamin D. D or precursors of vitamin D.
- It was first isolated from ergot, a fungus - It was first isolated from ergot, a fungus then from yeast. Ergosterol is less stable then from yeast. Ergosterol is less stable than cholesterol (than cholesterol (because of having 3 because of having 3 double bondsdouble 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 Steroids constitute an important
class of biological compounds.class of biological compounds. Steroids are usually found in Steroids are usually found in
association with fat. They can be association with fat. They can be separated from fats after separated from fats after saponification since they occur in saponification since they occur in the unsaponifiable residue.the unsaponifiable residue.
They are They are derivatives of cholesterolderivatives of cholesterol that is formed of steroid ring or that is formed of steroid ring or nucleus.nucleus.
Biologically important groups of Biologically important groups of substances, which contain this ring, are:substances, which 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 General consideration about naturally occurring steroidssteroids:
A typical member of this group A typical member of this group is cholesterolis cholesterol. . Certain facts have to be considered when drawing Certain facts have to be considered when drawing steroid formulasteroid formula:
1) There is always oxygen in the form of 1) There is always oxygen in the form of hydroxyl or hydroxyl or ketone on C3ketone 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 at C19 becomes a methylene group group at C19 becomes a methylene group (=CH2) and the ring B is opened, whereas, (=CH2) and the ring B is opened, whereas, this this methyl group is absent in female sex hormones methyl group is absent in female sex hormones (estrogens).(estrogens).
4) In estrogens (female sex hormones) ring A is 4) In estrogens (female sex hormones) ring A is aromatic and there is aromatic and 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 They are produced from oxidation of
cholesterol in the liver producing cholesterol in the liver producing cholic and cholic and chenodeoxycholic acidschenodeoxycholic acids that are conjugated that are conjugated with with glycine or taurineglycine or taurine to produce to produce glycocholic,glycocholic, glycochenodeoxycholic, glycochenodeoxycholic, taurocholictaurocholic and taurochenodeoxycholic and taurochenodeoxycholic acids. They react with sodium or potassium acids. They react with sodium or potassium to produce 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 Solubilizing cholesterol in bile and prevent
gall stone formation.gall stone formation.6.6.Choleretic action (stimulate their own Choleretic action (stimulate their own
secretion).secretion).7.7.Intestinal antiseptic that prevent Intestinal antiseptic that prevent
putrefactionputrefaction
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
