Lipid ChemistryPresented By

Ayman Elsamanoudy

Salwa Abo El-khair

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1. By the end of this chapter the student should be able to:

define lipids.

describe the biological importance of lipids.

point out basic lipid chemistry.

classify lipids.

explain the chemistry and main function of simple, compound

and derived lipids.

2. By the end of this chapter the student should be able to

apply biochemical knowledge on analyzing biochemical bases of

the diseases through case study.

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Objectives:

Introduction

Lipids are heterogeneous compounds related

to fatty acids.

They are insoluble in water

They are soluble in nonpolar solvents such as

>>>> ether, acetone and chloroform.

They are hydrophobic: due to predominance

of hydrocarbon chain

( – CH2 – CH2 – CH2 --) in their structure

Biological importance of lipids:

1- Lipids act as a source of energy: they yield

twice the energy produced by the same weight

of carbohydrates or proteins.

2- Lipids in adipose tissue serve as energy store.

3- They contain essential fatty acids.

4- They are the natural solvent for fat-soluble

vitamins.

Biological importance of lipids

5- Lipids have a role in protection and fixation of

internal organs as kidneys.

6- Lipids in myelin sheath of nerve fibers serve as

electrical insulator.

7- Lipids under the skin serve as thermal insulator.

Biological importance of lipids

8. Lipoproteins :

- Share in the structure of cell membrane

and mitochondria.

-They are important for lipid transport in

the blood.

9. Acetyl CoA: derived from fatty acids

oxidation is used for biosynthesis of many

important compound e.g. steroids.

Lipids Chemistry

Classification of

Lipids

Simple lipids Compound Lipids Derived Lipids

Classification of lipids

Simple lipids Compound lipids Derived lipids

-They are formed of fatty acids and alcohol

-They are formed of :

-Lipid component

+-Non-lipid component

-These are substances derived from simple lipids and compound lipids by hydrolysis.

Also, include

substance related to

lipids

1- Fats and Oils

2- Waxes

1- Phospholipids.

2- Glycolipids.

3- Sulpholipids.

4. lipoproteins

1- Fatty acids.

2- glycerol.

3- Steroid.

4- Isoprenoids.

5- Eicosanoids

Simple Lipids

Simple Lipids

Simple lipids are esters of fatty acids with different

types of alcohols.

The alcohol may be glycerol (trihydric alcohol) OR

other long alcohol.

R1 – COOH + R1 – OH RCOOR1 + H2O

Fatty acid + Alcohol Ester + Water

Simple lipids are classified into:

fats, oils and waxes, according to the type of alcohol they contain.

Simple Lipids

1-Fats and oils(neutral fats)

They are esters of :

fatty acids with glycerol.

They are similar chemically, but they differ in

physical properties:

as oils are liquid while

fats are solid at room temperature.

They are called triglycerides because they are

triesters formed of glycerol and 3 fatty acids.

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Simple Lipids

Triglycerides (TG) may be :

a- Simple TG: The fatty acids are the same

e.g. palmitic or stearic acids

forming>>>>

tripalmitate or tristearate respectively.

b- Mixed TG: Triglycerides with 3 different

fatty acids.

CH2 – OH

• 3R COOH + CH – OH

CH2 – OH

H2OO

CH 2 O C R

O

CH 2 O C R

O

CH 2 O C R

O

CH 2 O C R1

O

CH 2 O C R2

O

CH 2 O C R3

Triglycerides with 3

different fatty acids

3 fatty acids

glycerol

Simple

TAG

Mixed

TAG

Triglycerides

Triacylglycerols are composed of three

fatty acids each in ester linkage with

a single glycerol.

Triacylglycerol (TG)

Simple Lipids

2- Waxes

They are esters of

fatty acids + Long chain Monohydric alcohol.

They are solid at room temperature.

The most important waxes in human body are

cholesterol esters, which are present in blood and other

tissues.

WaxesFats and oils

SolidFats are solid

Oils are liquid

Consistency at room

temperature

Long chain alcohol & fatty

acid

Glycerol and 3 fatty acids Structure

AbsentPresent Glycerol

PresentAbsent Long chain alcohol

NegativePositiveAcrolein test

Not undergo rancidity undergo rancidityRancidity

Not Digested by lipase digested by lipase Digestion

Can not be utilizedCan be utilizedUtilization by human

body

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Activity

1-Give the hydrolytic product of :

- Tripalmitin.

- Cholesterol wax.

2-Compare between neutral fat and waxes.

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Choose the best correct answer :

Lipids are formed mainly of alcohol and fatty acids

combined together by:

a) ether link.

b) peptide bond.

c) glycosidic bond.

d) ester bond .

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Waxes :

a) are liquid at room temperature.

b) have positive acrolin test.

c) ester of long chain alcohol with a single fatty

acid

d) can be digested by human

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Ayman Elsamanoudy

Salwa Abo El-khair

Lipid ChemistryPresented By

Ayman Elsamanoudy

Salwa Abo El-khair

2

Glycerol Chemistry : trihydric alcohol

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Physical properties:

1- It is colourless

2- viscid fluid

3- with sweet taste.

4- It is miscible with water in all proportions.

Chemical properties

1- Can combine with one or more fatty acids by

ester bonds forming >>>> mono, di or

triacylglycerol.

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2- Acrolin Test:

With strong dehydrating agents, as concentrated

sulphuric acid, glycerol can be converted to >>>>

acrolein that has very irritating pungent odour.

Importance of glycerol

It is used in pharmaceutical and cosmetic

preparations.

It is used as explosive in the form of

trinitroglycerine.

It is used in medicine as a vasodilator agent in

coronary heart diseases in the form of

nitroglycerine.

Fatty acids

These are monocarboxylic organic acids, which

usually contain an even number of carbon atoms.

The general formula of fatty acid is R-COOH

CH3 – CH2 – CH2 – CH2 – CH2 – COOH

They are further classified into:

Saturated & Unsaturated fatty acids

according to absence or presence of double bonds.

Fatty acids

Fatty acids

The carbon chain of fatty acids are numbered as:

1- starting from carboxylic group: there are

two systems:

a- the carboxylic group is number 1 and

proceed toward the CH3

b- by using the α C adjacent to COOH and

continue β , γ , δ , ε , etc.

Fatty acids

6 5 4 3 2 1

CH3 – CH2 – CH2 – CH2 – CH2 – COOH

ε δ γ β α

Fatty acids

2- starting from the terminal CH3 group or

omega carbon:

ώ1 ώ2 ώ3 ώ4 ώ5 ώ6

CH3 – CH2 – CH2 – CH2 – CH2 – COOH

Fatty acids

6 5 4 3 2 1

CH3 – CH2 – CH2 – CH2 – CH2 – COOH

ε δ γ β α

ώ1 ώ2 ώ3 ώ4 ώ5 ώ6

Fatty acids

A. Saturated fatty acids

They have no double bonds.

They have the general formula :

CH3 – (CH2)n – COOH.

They are further classified, according to the

number of carbon atoms, into:

Short chain & Long chain fatty acids.

Long chain FAShort chain FA

More than 10

carbons

Less than 10

carbons ( 2C to

10C )

Number of carbon

atoms

Solid Liquid Consistency at room

temperature

Nonvolatile Volatile Volatility

Insoluble Soluble Solubility in water

Palmetic (16 C)

Stearic (18 C)

Acetic (2 C)

Butyric (4 C)

Examples

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A fatty acid is composed of a

long hydrocarbon chain

(“tail”) and a terminal

carboxyl group (or “head”).

16:0 palmitic acid

The following table shows the formula of the most common saturated fatty acids.

Common name Formula

Short chain FA

Acetic acid (2C) CH3 – COOH

Butyric acid (4C) CH3 – (CH2)2 – COOH

Caproic acid (6C) CH3 – (CH2)4 – COOH

Long chain FA

Palmitic acid (16C) CH3 – (CH2)14 – COOH

Stearic acid (18C) CH3 – (CH2)16– COOH

Arachidic acid (20C) CH3 – (CH2)18– COOH

Lignoceric acid (24C) CH3 – (CH2)22– COOH

B- Unsaturated fatty acids• They have one or more double bonds.

• Most of the double bonds are of cis type.

• cis isomer trans isomer

• In case of >2 double bonds, each 2 double bonds are separated by methylene (CH2) group.

•

-CH=CH-CH2-CH=CH-CH2-

Eliadic acid (trans form)Oleic acid (cis form)

For example:

Fatty acids

B- Unsaturated fatty acids

They have one or more double bonds.

I. Mono-unsaturated (monoethenoid) fatty

acids:

Contains one double bond

Their general formula is

CH3 – (CH2)n – CH = CH – (CH2)x –COOH

Fatty acidsB- Unsaturated fatty acids

I. Mono-unsaturated (monoethenoid) fatty acids:

contains one double bond e.g.:

Palmitoleic acid :(16:1Δ9,ω7)

CH3 – (CH2)5 – CH = CH – (CH2)7 –COOH

n = 5 x = 7

Contain 16 C , one double bond

Double bond between C9 and C10 from COOH

ώ7 means: double bond between C7 and C8

from terminal CH3 ( ώ1 )

Fatty acidsB- Unsaturated fatty acids

I. Mono-unsaturated (monoethenoid) fatty

acids:

contains one double bond e.g.:

Palmitoleic acid :(16:1Δ9,ω7)

CH3 – (CH2)5 – CH = CH – (CH2)7 –COOH

Oleic acid : (18:1Δ9,ω9)

CH3 – (CH2)7 – CH = CH – (CH2)7 –COOH

Nervonic acid :(24:1Δ15,ω9)

CH3 – (CH2)7 – CH = CH – (CH2)13 –COOH

II. Polyunsaturated (polyethenoid) fatty acids:

Contains more than one double bond.

Linoleic acid : (18C:2 Δ9,12, ω6)

CH3 – (CH2)4 – CH = CH – CH2 – CH = CH – (CH2)7 – COOH

Linolenic acid : (18C:3 Δ9,12,15, ω3)

CH3–CH2–CH=CH–CH2–CH=CH–CH2–CH=CH–(CH2)7–COOH

13 12 11 10 9

16 15 14 13 12 11 10 9

Arachidonic acid :

(20C: 4 Δ5,8,11,14, ω6)

CH3–(CH2)4–CH=CH–CH2–CH=CH–CH2–CH=CH–CH2CH=CH–(CH2)3–COOH

15 14 13 12 11 10 9 8 7 6 5

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The packing of

fatty acids into

stable aggregates

Essential fatty acids Def:

They are polyunsaturated fatty acids

i.e. fatty acids, which contain more than one

double bond.

They must be taken in diet because the body cannot

synthesize them, as the enzymes that are needed for

their synthesis are absent in humans.

Examples :

Linoleic (18C+ 2double bonds),

Linolenic (18C+ 3double bonds) and

Arachidonic acids (20C+ 4double bonds).

Importance of Essential Fatty Acids

1. They are essential for growth.

2. They are essential for phospholipids formation.

3. Arachidonic acid, which is one of the essential fatty

acids, is important for biosynthesis of

prostaglandins.

4. They form cholesterol esters (less liable to be

deposited in blood vessels)>>>>

So, protect against Atheroscelerosis.

Fatty AcidsSaturated FA

Short chain

Saturated FA

Long chain

Mono-

unsaturated

Poly-

unsaturated

Acetic acid

(2C)

Palmitic acid

(16C)

Palmitoleic acid

(16:1Δ9,ω7)

Linoleic acid :

(18C:2 Δ9,12, ω6)

Butyric acid

(4C)

Stearic acid

(18C)

Oleic acid :

(18:1Δ9,ω9)

Linolenic acid

(18C:3 Δ9,12,15, ω3)

Caproic acid

(6C)

Arachidic acid

(20C)

Nervonic acid

(24:1Δ15,ω9)

Arachidonic acid

(20C: 4 Δ5,8,11,14, ω6)

Lignocericacid (24C)

Ayman Elsamanoudy

Salwa Abo El-khair

Lipid ChemistryPresented By

Ayman Elsamanoudy

Salwa Abo El-khair

3

General properties of fatty acids They usually contain an even number of carbon

atoms.

They have straight chains.

They may be saturated or unsaturated.

Unsaturated fatty acids are more reactive than

saturated fatty acids.

Some fatty acids are hydroxylated eg. cerebronic

acid.

Lower FAs are soluble in water & this solubility

decreases with increasing chain length.

Palmitic, stearic and oleic acids make up the bulk of

animal depot fat.

Physical properties of fatty acids

1. They are colourless, odourless and tasteless.

2. Solubility in water:

Short chain fatty acids are soluble in water.

The solubility decreases with the increase in

chain length.

Long chain fatty acids are insoluble in water

but soluble in nonpolar solvents.

3. Melting point:

It depends on:

- The length of the chain of fatty acid

- The degree of unsaturation.

Short chain and unsaturated fatty acids:

- They have lower melting point.

- They are liquid at room temperature.

Long chain saturated fatty acids:

-They have higher melting point.

- They are solid at room temperature.

4. Optical (Geometric) stereoisomerism:

Fatty acids that contain double bond can bepresent in cis (mostly) and trans stereoisomericforms.

Cis configuration means that the groups aroundthe double bond are on the same side of the bond.

Trans configuration means that the groupsaround the double bond are on the opposite sidesof the bond.

4. Optical (Geometric) stereoisomerism:

Fatty acids that contain double bond: cis (mostly)

and trans forms.

For example:

oleic acid, which is a cis form, and its isomer

eliadic acid, which is a trans form.

Eliadic acid (trans form)Oleic acid (cis form)

For example:

Eliadic acid (trans form)Oleic acid (cis form)

For example:

Rancidity

Def:

Rancidity is a condition in which fat attains

a bad taste and disagreeable odour.

Types of rancidity

There are 2 types of rancidity:

Hydrolytic rancidity

Oxidative rancidity

There are 2 types of rancidity:

Hydrolytic rancidity

Fats are hydrolyzed into glycerol and fatty acids in

presence of :

- Moisture .

- Warm temperature

- Bacterial enzymes

Oxidative rancidity

It occurs by oxidation of unsaturated fatty acids

present in fats and oils forming lipid peroxides,

fatty aldehydes, ketones and short chain fatty

acids.

Predisposing factors of rancidity

Rancidity is predisposed by:

Light.

Moisture.

Warm temperature.

Effects of rancidity

Rancidity leads to:

Fats and oils attain bad taste.

Fats and oils attain disagreeable odour.

Production of toxic compounds as lipid

peroxidies, aldehydes and ketones.

Prevention of rancidity:

Avoid exposure of fats to light, moisture and high

temperature.

Addition of antioxidants to fats and oils specially the

natural antioxidant tochopherol (vitamin E).

Activity 1- Differentiate between short and long chain FA.

2- Differentiate between saturated and unsaturated

FA.

3- Essential FA (def. examples and importance).

4- What is acrolin test ,mention its biochemical use.

5- Mention three uses of glycerol.

6- Rancidity (types, effects and prevention)

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Choose the correct answer:

Example of saturated FA:

a) arachidonic acid

b) Oleic acid

c) palmitic acid

d) Linoleic acid

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The following are essential fatty acids except:

a) palmitoleic acid

b) arachidonic

c) linolenic

d) Linoleic acid

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Regarding Eliadic acid (18C:1Δ9,ω9), all are

true EXCEPT

a) It is non-essential FA

b) It is the trans isomer form of linoleic

acid

c) It is 18 C

d) It is monounsaturated FA

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Rancidity is a process of oxidation concerning :

a) short chain FA

b) saturated FA.

c) hydroxy FA

d) unsaturated FA

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Concerning Linoleic acid (18C:2Δ9,12,ω6) ,what

is not true:

a) it is unsaturated FA

b) It contains 2 double bonds

c) The last double is 6 carbon atom from its last C.

d) The first double bond lies between C8-C9.

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Rancidity can be prevented by addition of :

a) vitamin B

b) vitamin D

c) Vitamin E

d) vitamin K

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Ayman Elsamanoudy

Salwa Abo El-khair