LIPIDSLIPIDS

DefinitionDefinition:: Made up of C, H and O

Lipids are hydrophobic compounds. Lipids are hydrophobic compounds.

insoluble or poorly soluble in water, insoluble or poorly soluble in water,

Readily soluble in non-polar solvents Readily soluble in non-polar solvents such as ( ether, benzene, acetone, such as ( ether, benzene, acetone, chloroform)chloroform)

Biological Functions of Biological Functions of LipidsLipids

As an As an energy sourceenergy source, lipids provide 9 kcal of , lipids provide 9 kcal of energy per gramenergy per gram

Triglycerides provideTriglycerides provide energy storageenergy storage in adipocytes in adipocytes Phosphoglycerides, sphingolipids, and steroids are Phosphoglycerides, sphingolipids, and steroids are

structural componentsstructural components of cell membranes of cell membranes SteroidSteroid hormoneshormones are critical intercellular are critical intercellular

messengersmessengers Lipid-soluble Lipid-soluble vitaminsvitamins (A, E, D, K) (A, E, D, K) Dietary fat acts as a Dietary fat acts as a carrier of lipid-solublecarrier of lipid-soluble

vitamins into cells of small intestinevitamins into cells of small intestine Provide Provide shock absorptionshock absorption and and insulationinsulation

Biomedical importance of Biomedical importance of lipidslipids::

1.1. They are a major source of energy; the They are a major source of energy; the yield from the oxidation of fatty acids is yield from the oxidation of fatty acids is

9 kcal/g fat compared to 4 kcal/g protein 9 kcal/g fat compared to 4 kcal/g protein or carbohydrate.or carbohydrate.

2. Fat stored in adipose tissue serves as 2. Fat stored in adipose tissue serves as thermal insulator in the subcutaneous thermal insulator in the subcutaneous tissue and protective around certain tissue and protective around certain organs (e.g. kidney).organs (e.g. kidney).

3. Lipids act as electrical insulators in 3. Lipids act as electrical insulators in myelinated nerves to allow rapid myelinated nerves to allow rapid propagation of nerve impulses.propagation of nerve impulses.

4. 4. Cholesterol is an important constituent Cholesterol is an important constituent of the cell membrane and is essential for of the cell membrane and is essential for the synthesis of steroid hormones, bile the synthesis of steroid hormones, bile acids and vitamin D.acids and vitamin D.

5. 5. Fat-soluble vitamins, steroid hormones Fat-soluble vitamins, steroid hormones and eicosanoids play important and eicosanoids play important regulatory roles in the body.regulatory roles in the body.

7. Lipoproteins (e.g. LDL & HDL) are a mean7. Lipoproteins (e.g. LDL & HDL) are a mean

for transporting lipids in blood.for transporting lipids in blood.

8. Imbalance in lipid metabolism can lead to8. Imbalance in lipid metabolism can lead to

major clinical problems such as obesity major clinical problems such as obesity and atherosclerosisand atherosclerosis

Fatty AcidsFatty Acids Fatty acids are water-insoluble. Fatty acids are water-insoluble. Long straight-chain carboxylic acids Long straight-chain carboxylic acids

– no branchingno branching Most common chains range from 10–20 carbons in Most common chains range from 10–20 carbons in

lengthlength Can be saturated (containing no double bonds) or Can be saturated (containing no double bonds) or

unsaturated (containing one or more double bonds unsaturated (containing one or more double bonds that are always separated at 3 carbon intervals), but that are always separated at 3 carbon intervals), but usually no other functional groups presentusually no other functional groups present

The general formula of saturated fatty acids is:The general formula of saturated fatty acids is: CH CH3 3 - ( CH- ( CH22))n n – COOH – COOH– Any fatty acid that cannot be synthesized by the Any fatty acid that cannot be synthesized by the

body is called an body is called an essential fatty acidessential fatty acid

Fatty Acid Fatty Acid NomenclatureNomenclature

Nomenclature reflects location of Nomenclature reflects location of double bondsdouble bonds

also used are common names (e.g., also used are common names (e.g., oleic, stearic, palmitic)oleic, stearic, palmitic)

Carbon atoms in a fatty acid are Carbon atoms in a fatty acid are numbered by 2 different systemsnumbered by 2 different systems::

1.1. Beginning from the carboxyl carbonBeginning from the carboxyl carbon

((ΔΔ delta end) as carbon 1, where delta end) as carbon 1, where numeric designation of the fatty acid shows the numeric designation of the fatty acid shows the

number of carbon atomsnumber of carbon atoms

2- followed by the number of double bonds,2- followed by the number of double bonds,

3- then the site of unsaturation.3- then the site of unsaturation.

COOH

2

1 3

4

15

16

Palmitic acid: Palmitic acid:

CHCH33(CH(CH22))1414COOH ; 16:0COOH ; 16:0 (16:0 indicates a fatty acid with 16 (16:0 indicates a fatty acid with 16

carbons and no double carbons and no double bonds).bonds).

Oleic acid: Oleic acid:

CHCH33(CH(CH22))77C=C(CHC=C(CH22))77COOH ; 18:1 COOH ; 18:1 ΔΔ 99 (18:1 (18:1 ΔΔ 9 indicates a fatty acid with 9 indicates a fatty acid with

18 carbons and one double bond 18 carbons and one double bond between carbons 9 and 10).between carbons 9 and 10).

Linoleic acid:Linoleic acid:

CHCH33 (CH (CH22) ) 44C=CCHC=CCH22C=C(CHC=C(CH22) ) 77COOH ; 18:2 COOH ; 18:2 ΔΔ 9,129,12

(18:2 (18:2 ΔΔ 9,12 indicates a fatty acid with 18 9,12 indicates a fatty acid with 18 carbons and 2 double bonds between carbons and 2 double bonds between carbons 9 and 10 and carbons 12 and13).carbons 9 and 10 and carbons 12 and13).

Linolenic acid: Linolenic acid:

CHCH33CHCH22C=CCHC=CCH22C=CCHC=CCH22C=C(CHC=C(CH22) ) 77COOH; 18:3 COOH; 18:3 ΔΔ 9,12,15 9,12,15

(18:3 (18:3 ΔΔ 9,12,15 indicates a fatty acid with 9,12,15 indicates a fatty acid with 18 carbons and 3 double bonds between 18 carbons and 3 double bonds between carbons 9 and 10, carbons 12 and 13 and carbons 9 and 10, carbons 12 and 13 and carbons 15 and 16).carbons 15 and 16).

Arachidonic acid:Arachidonic acid:

CHCH33 (CH (CH22) ) 33(CH(CH22C=C) C=C) 44(CH(CH22) ) 33COOH; 20:4 COOH; 20:4 ΔΔ 5,8,11,145,8,11,14

(20:4 (20:4 ΔΔ 5,8,11,14 indicates a fatty acid with 20 5,8,11,14 indicates a fatty acid with 20 carbonscarbons

and 4 double bonds between carbons 5 and 6,and 4 double bonds between carbons 5 and 6,

carbons 8 and 9, carbons 11 and 12 and carbons 8 and 9, carbons 11 and 12 and

carbons 14 and 15).carbons 14 and 15).

2. Beginning with the terminal methyl 2. Beginning with the terminal methyl carbon carbon

(known as omega (known as omega ώώ carbon) as carbon 1, carbon) as carbon 1, where where ώώ-3 for example indicates that;-3 for example indicates that; The closest double bond to the terminal The closest double bond to the terminal

methyl methyl group begins after 3 carbons from that end. group begins after 3 carbons from that end. Therefore,Therefore, linoleic acid ; is an linoleic acid ; is an ώώ -6 fatty acid -6 fatty acidCHCH33 (CH (CH22) ) 44C=CCHC=CCH22C=C(CHC=C(CH22) ) 77COOHCOOH ώώ -6,18:2 -6,18:2 ΔΔ 9,12 9,12

linolenic acid ;is an linolenic acid ;is an ώώ -3 fatty acid. -3 fatty acid.CHCH33CHCH22C=CCHC=CCH22C=CCHC=CCH22C=C(CHC=C(CH22) ) 77COOHCOOH ώώ -3,18:3 -3,18:3ΔΔ9,12,159,12,15

Fatty Acid PropertiesFatty Acid Properties Melting point increases with increasing carbon Melting point increases with increasing carbon

numbernumber Melting point of a saturated fatty acid is higher Melting point of a saturated fatty acid is higher

than an unsaturated fatty acid with the same than an unsaturated fatty acid with the same number of carbonsnumber of carbons

Typical saturated fatty acids are tightly packed Typical saturated fatty acids are tightly packed togethertogether

ciscis double bonds prevent good alignment of double bonds prevent good alignment of molecules in unsaturated fatty acids leading to molecules in unsaturated fatty acids leading to poor packingpoor packing

Double bonds lower melting point relative to Double bonds lower melting point relative to saturated acidsaturated acid

Common Fatty AcidsCommon Fatty Acids

Saturated & Unsaturated Fatty AcidsSaturated & Unsaturated Fatty AcidsA. Saturated Fatty Acids:A. Saturated Fatty Acids:

NameName No of No of CarbonCarbon Atoms Atoms

No of DoubleNo of Double Bonds Bonds

Lauric (12:0)Lauric (12:0) 1212 00

Myristic (14:0)Myristic (14:0) 1414 00

Palmitic (16:0)Palmitic (16:0) 1616 00

Stearic (18:0)Stearic (18:0) 1818 00

Saturated fatty acids do not have double bondsSaturated fatty acids do not have double bonds..

They are formed inside the bodyThey are formed inside the body..

Saturated Fatty Acids CH3 CH2 CH2 CH2 CH2 CH2 CH2 C OH

O1245678 3

Octanoic Acid

B.B. Unsaturated Unsaturated FattyFatty Acids: Acids:NameName No of CarbonNo of Carbon

Atoms Atoms No of DoubleNo of Double Bonds Bonds

Palmitoleic (16:1)Palmitoleic (16:1) 1616 11

Oleic (18:1)Oleic (18:1) 1818 11

Linoleic (18:2)Linoleic (18:2) 1818 22

Linolenic (18:3)Linolenic (18:3) 1818 33

Arachidonic (20:4)Arachidonic (20:4) 2020 44

The first double bond is usually at the ninth carbonThe first double bond is usually at the ninth carbonThe double bond is normally in a The double bond is normally in a cis cis configuration configurationDouble bonds lower the melting temperatureDouble bonds lower the melting temperatureThe The ciscis configuration doesn’t allow fatty acids to configuration doesn’t allow fatty acids to pack as close togetherpack as close together

Saturated vs. Unsaturated Fatty Saturated vs. Unsaturated Fatty AcidsAcids

saturatedsaturated: the SFA’s of a lipid have no : the SFA’s of a lipid have no double bonds between carbons in chaindouble bonds between carbons in chain

polyunsaturatedpolyunsaturated: more than one : more than one double bond in the chaindouble bond in the chain

most common polyunsaturated fats most common polyunsaturated fats contain the polyunsaturated fatty acids contain the polyunsaturated fatty acids (PUFAs) (PUFAs) oleicoleic, , linoleiclinoleic and and linoleniclinolenic acid acid

unsaturated fats have lower melting unsaturated fats have lower melting points points

stearic (SFA) melts at 70stearic (SFA) melts at 70ooC, oleic (PUFA) C, oleic (PUFA) at 26at 26ooCC

Unsaturated fatty acids have one or more Unsaturated fatty acids have one or more double bonds. There are 2 types:double bonds. There are 2 types:

Essential fatty acidsEssential fatty acids::

These fatty acids are with more than one These fatty acids are with more than one double bond, e.g. linoleic, linolenic and double bond, e.g. linoleic, linolenic and arachidonic,arachidonic,

they are not formed in the body and should they are not formed in the body and should be obtained from the diet.be obtained from the diet.

Non-essential fatty acidsNon-essential fatty acids: : These can be synthesized in the body.These can be synthesized in the body.

Unsaturated Fatty Acids CH3 CH2 CH2 CH2 CH2 CH2 CH2 C OH

O1245678 3

CH3 CH2 CH2 CH2 CH2 CH2 CH2 C OH

O1245678 3

3 - Octenoic Acid

3, 6 - Octadienoic Acid

Short hand: 8:1 (3)

8:2 (3,6)

Polyunsaturated Fatty Acids

Linoleic acid: Cis, cis, 9, 12 - Octadecadienoic acid

Linolenic acid: Cis, cis, cis 9, 12, 15 - Octadecatrienoic acid

Arachidonic acid: Cis, cis, cis, cis 5, 8, 11, 14 - Eicosatetraenoic acid

 

Linoleic Acid

Linolenic Acid

Arachidonic Acid

Saturated vs. Unsaturated Saturated vs. Unsaturated FatsFats

saturated fats tightly packed, clog saturated fats tightly packed, clog arteries as arteries as atherosclerosisatherosclerosis

because of double bonds, because of double bonds, polyunsaturated fats do not pack well polyunsaturated fats do not pack well -- like building a wall with bricks vs. -- like building a wall with bricks vs. irregular-shaped objectsirregular-shaped objects

plant fats are much higher in PUFA’s plant fats are much higher in PUFA’s than animal fatsthan animal fats

Cis 9 - Octadecenoic Acid (oleic)

Trans 9 - Octadecenoic Acid (elaidic acid)

O

CH3(CH2)7 C C (CH2)7 C OH

HH

910 O

CH3(CH2)7 C C (CH2)7 C OH

H

H

Cis And Trans Fatty Acids

Naturally-occurring fatty acids R CH2 CH CH CH2 CH CH CH2 C OH

O

7 6 5 4 3

1. Cis form

2. Not conjugated --- isolated double bond.

3. Even numbered fatty acids.

CLASSIFICATION OF FATTY ACIDS PRESENT AS GLYCERIDES IN FOOD FATS

 

I. Saturated Fatty Acids  

Butyric Butanoic CH3(CH2)2COOH butterfat

Caproic Hexanoic CH3(CH2)4COOH butterfat, coconut and palm nut oils

Caprylic Octanoic CH3(CH2)6COOH coconut and palm nut oils, butterfat

Capric Decanoic CH3(CH2)8COOH coconut and palm nut oils, butterfat

Lauric Dodecanoic CH3(CH2)10COOH coconut and palm nut oils, butterfat

Myristic Tetradecanoic CH3(CH2)12COOH coconut and Palm nut oil, most animal and plant fats

Palmitic Hexadecanoic CH3(CH2)14COOH practically all animal and plant fats

Stearic Octadecanoic CH3(CH2)16COOH animal fats and minor component of plant fats

Arachidic Eicosanoic CH3(CH2)18COOH peanut oil

Common Name

Systematic Name

Formula Common source

 Common Name

Systematic Name

Formula Common source

II. Unsaturated Fatty Acids  A. Monoethenoic Acids

 Oleic Cis 9-octadecenoic C17H33COOH plant and animal fats

Elaidic Trans 9-Octadecenoic C17H33COOH animal fats

B. Diethenoic Acids

Linoleic 9,12-Octadecadienoic C17H31COOH peanut, linseed, and cottonseed oils

C. Triethenoid Acids Linolenic 9,12,15-Octadecatrienoic C17H29COOH linseed and other seed

oilsEleostearic 9,11,13-Octadecatrienoic C17H29COOH peanut seed fats

D. Tetraethenoid AcidsMoroctic 4,8,12,15-Octadecatetraenoic C17H27COOH fish oils

Arachidonic 5,8,11,14-EicosatetraenoicC19H31COOH traces in animal fats

Common and Systematic Names of Fatty Common and Systematic Names of Fatty AcidsAcids  

Common Name

Systematic Name

Formula Common source 

A. Monoethenoic Acids 

Oleic Cis 9-octadecenoic C17H33COOH plant and animal fats

Elaidic Trans 9-Octadecenoic C17H33COOH animal fats

B. Diethenoic Acids

Linoleic 9,12-Octadecadienoic C17H31COOH peanut, linseed, and cottonseed oils

C. Triethenoid Acids Linolenic 9,12,15-Octadecatrienoic C17H29COOH linseed and other seed

oils

Eleostearic9,11,13-Octadecatrienoic C17H29COOH peanut seed fats

D. Tetraethenoid Acids

Moroctic 4,8,12,15-Octadecatetraenoic C17H27COOH fish oils

Arachidonic5,8,11,14-Eicosatetraenoic C19H31COOH traces in animal fats

Biomedical importance of fatty acids:Biomedical importance of fatty acids: Human body can synthesize various fatty acids Human body can synthesize various fatty acids

with the exception of;with the exception of;

““linoleic” and “linolenic” acids; this is because linoleic” and “linolenic” acids; this is because body tissues cannot introduce double bonds body tissues cannot introduce double bonds beyond the beyond the ΔΔ 9 position. 9 position.

In contrast, plants are able to introduce double In contrast, plants are able to introduce double

bonds at the bonds at the ΔΔ 12 and 12 and ΔΔ 15 positions. 15 positions.

Therefore, linoleic acid and linolenic acid are Therefore, linoleic acid and linolenic acid are considered as nutritionally essential fatty acids,considered as nutritionally essential fatty acids,

and must be supplied in a diet of plant origin or and must be supplied in a diet of plant origin or from animals that have consumed these plant from animals that have consumed these plant fats.fats.

1. Dietary 1. Dietary ώώ -3 fatty acids (in fish oil and plant -3 fatty acids (in fish oil and plant fats)fats)

can reduce serum triglycerides, thrombosis andcan reduce serum triglycerides, thrombosis and the risk of cardiovascular mortality. the risk of cardiovascular mortality.

2- 2- ώώ -6 fatty acids (in olive oil and corn oil) -6 fatty acids (in olive oil and corn oil)

lower plasma cholesterol and protect against lower plasma cholesterol and protect against coronary heart disease.coronary heart disease.

3-Generally, a high ratio of polyunsaturated fatty3-Generally, a high ratio of polyunsaturated fatty

acids to saturated fatty acids in the diet is a acids to saturated fatty acids in the diet is a major factor to prevent coronary heart disease.major factor to prevent coronary heart disease.

Eicosanoids: Eicosanoids: Prostaglandins, Prostaglandins, Leukotrienes, and Leukotrienes, and

ThromboxanesThromboxanes Fatty acids which can’t be synthesized by Fatty acids which can’t be synthesized by

the body are the body are essential fatty acidsessential fatty acids– Linoleic acid Linoleic acid is an essential fatty acid required is an essential fatty acid required

to make arachadonic acidto make arachadonic acid Arachidonic acid (20 C) is the eicosanoid Arachidonic acid (20 C) is the eicosanoid

precursorprecursor Eicosanoids are three groups of structurally Eicosanoids are three groups of structurally

related compoundsrelated compounds– Prostaglandins Prostaglandins – LeukotrienesLeukotrienes– ThromboxanesThromboxanes

COO-

arachadonic acid

ProstaglandinsProstaglandins Potent biological moleculesPotent biological molecules They act like hormones in controlling the They act like hormones in controlling the

body’s processes body’s processes StructureStructure

– Synthesized from 20-carbon unsaturated fatty Synthesized from 20-carbon unsaturated fatty acidsacids

– Cyclic compounds including a 5-carbon ring Cyclic compounds including a 5-carbon ring Names are based on ring substituents and Names are based on ring substituents and

number of side-chain double bondsnumber of side-chain double bonds Made in most tissuesMade in most tissues

– Exert their effects on cells that produce them Exert their effects on cells that produce them and cells in the immediate vicinityand cells in the immediate vicinity

Biological Processes Biological Processes Regulated by EicosanoidsRegulated by Eicosanoids

1.1. Blood clottingBlood clotting– Thromboxane AThromboxane A22 stimulates constriction stimulates constriction

of blood vessels and platelet aggregationof blood vessels and platelet aggregation– Prostacyclin dilates blood vessels and Prostacyclin dilates blood vessels and

inhibits platelet aggregationinhibits platelet aggregation

2.2. Inflammatory responseInflammatory response– Prostaglandins mediate aspects of Prostaglandins mediate aspects of

inflammatory responseinflammatory response

3.3. Reproductive systemReproductive system– Stimulation of smooth muscle by PGEStimulation of smooth muscle by PGE22

Biological Processes Biological Processes Regulated by EicosanoidsRegulated by Eicosanoids

4.4. Gastrointestinal tractGastrointestinal tract– Prostaglandins inhibit gastric secretionProstaglandins inhibit gastric secretion– Inhibition of hormone-sensitive lipasesInhibition of hormone-sensitive lipases– Prostaglandins increase secretion of protective Prostaglandins increase secretion of protective

mucusmucus

5.5. KidneysKidneys– Prostaglandins dilate renal blood vesselsProstaglandins dilate renal blood vessels– Results in increased water and electrolyte Results in increased water and electrolyte

excretionexcretion

6.6. Respiratory tractRespiratory tract– Leukotrienes promote the constriction of bronchiLeukotrienes promote the constriction of bronchi– Prostaglandins promote bronchodilationProstaglandins promote bronchodilation

Structures of Four Structures of Four ProstaglandinsProstaglandins

Aspirin and ProstaglandinsAspirin and ProstaglandinsAspirin inhibits prostaglandin synthesis by Aspirin inhibits prostaglandin synthesis by acetylating cyclooxygenase, an enzyme acetylating cyclooxygenase, an enzyme necessary for prostaglandin synthesisnecessary for prostaglandin synthesis

Overview of Prostaglandin Overview of Prostaglandin Synthesis From Arachidonic Synthesis From Arachidonic

AcidAcid