12/14/2023
Dr.Shaymaa Galal lecturer of Biochemistry
Dr. Shaymaa Galal
lecturer of Biochemistry
LIPIDS (Greek: lipos, means fat or lard)
❑ The lipids are a heterogeneous group of compounds, including fats, oils,
steroids, waxes, and related compounds, that are related more by their physical
than by their chemical properties (have a distinguished functional group or
structural features).
❑ Lipids are insoluble in water and highly soluble in one or more of the solvents:
ether, chloroform, benzene and acetone. This property sets them apart from
proteins, carbohydrates,, nucleic acids and other biomolecules.
❑ Lipids are important feature in cell membranes, fatsteroid hormones.
soluble vitamins, and
Hydrophobic in nature!
Main Composition
⚫Mainly contains C, H & O atoms.
⚫Constituents of:
⚫Cell membranes of animal & plant cells
⚫Food storage molecules
⚫Intermediaries in signaling pathways
⚫Vitamins A, D, E and K
⚫Cholestrol
,
❑Make up 18–25% of body mass in lean adults.
❑Formed of long-chain hydrocarbon groups, also contain oxygen,
phosphorus, nitrogen and sulfur.
Properties of Lipids
❑Insoluble in water, but soluble in organic solvent.
❑Actually or potentially related to fatty acids.
❑It can be used as a source of energy by animals.
Functions and Biological Importance of Lipids
❑
❑
❑
❑
❑
❑
Storage form of energy and acts as fuel to the body (9 kcal/gm)
Important dietary components because of their high energy value
and also because of the fat-soluble vitamins and the essential fatty
acids contained in the fat of natural foods.
Structural components of biomembranes.
Serve as thermal insulators in the subcutaneous tissues and
around certain organs.
The Nervous system is particularly rich in lipids. Nonpolar lipids
act as electrical insulators, allowing rapid propagation of waves
and depolarization along myelinated nerves.
Provide shape and contour to the body.
Functions and Biological Importance of Lipids
Source of energy/Fuel to
body
Lipoproteins/Phospholi pids
Bile salts
Importance of
LIPIDS
Protection & Paddling of
internal Organs
Thermal & Electrical
insulator
Prostaglandins
Vitamins
Building
materials(Hormones)
CLASSIFICATION OF LIPIDS
1.Simple lipids: Esters of fatty acids with various alcohols.
a)Triacylglycerols/Triglycerides
• Fats: Esters of short or medium chain fatty acids with glycerol. Eg.triolein, tripalmitin.
▪ Oils are fats in the liquid state. Eg.- corn, groundnut oil.
b)Waxes:
▪ True Waxes: Esters of fatty acids (C14 – 36) with higher
molecular weight monohydric long chain alcohols (C16 - 30). e.g.
Bees wax, lanolin, spermaceti oil.
▪ Other waxes: cholesterol ester, Vit. A ester, Vit. D ester.
Fats & Oils – Triglycerides Synthesis (Dehydration synthesis)
⚫Two kinds of molecules
⚫Glycerol
⚫Fatty acids
2. Complex/Compound lipids: Esters of fatty acids containing
groups in addition to an alcohol and a fatty acid.
a) Phospholipids: Lipids containing, in addition to fatty acids and
an alcohol, a phosphoric acid residue. They frequently have
nitrogen- containing bases and other substituents, eg, in
i)Glycerophospholipids: the alcohol is glycerol
ii)Sphingophospholipids: the alcohol is sphingosine.
b) Glycolipids (glycosphingolipids): Lipids containing a fatty acid,
sphingosine, and carbohydrate. –Cerebosides
– Gangliosides
c)Lipoproteins: macromolecular complexes of lipids with proteins.
d) Other complex lipids: Lipids such as sulfolipids, aminolipids and
Lipopolysachharides may also be placed in this category.
3. Derived and Precursor lipids: Derived from simple lipids or
complex lipids on hydrolysis. These include
o Fatty acids and Glycerol, Monoacyl and Diacylglycerols
Steroids lipids with cyclopentanoperhydrophenanthrene (steroid)
ring. e.g. cholesterol and its derivatives- bile acids, hormones,
Ergosterol.
o Lipid-soluble vitamins, eicosanoids-arachidonic acid derivativesPG,TXA2,
4.Miscellaneous lipids: These include a large number of compounds
possessing the characteristics of lipids e.g., carotenoids, squalene,
hydrocarbons such as pentacosane (in bees wax), terpenes etc.
➢ Neutral Lipids: the lipids which are uncharged are referred to as
neutral lipids. These are mono, di, and triacylglycerols, cholesterol
Fatty acids
▪ Fatty acids are simplest form of lipids. Fatty acids are aliphatic
carboxylic acid with hydrocarbon side chain.
Have the general formula R-(CH2)n-COOH where, R -Alkyl /
hydrocarbon chain and COOH- Carboxyl end.
Occurrence:
▪ They occur mainly as esters in natural fats and oils but do occur in
the unesterified form as free fatty acids (Free fatty acids are formed
only during metabolism), a transport form found in the plasma.
▪ Fatty acids that occur in natural fats are usually straight-chain
derivatives containing an even number of carbon atoms.
Even and odd carbon fatty acids:
❑ Most of the Fatty acids that occur in natural lipids are of even
carbons (usually 14C – 20C). This is due to biosynthesis of fatty
acids mainly occurs with the sequential addition of 2 carbon units.
Palmitic acid (16C) and Stearic acid (18C) are most common.
Propionic acid (3C) and valeric acid (5C) are common odd chain
fatty acids.
Nomenclature:
➢ It is based on hydrocarbon from which it is derived. After the name of the
parent hydrocarbon with suffix –anoic acid for saturated fatty acid, –enoic acid
for unsaturated fatty acid.
8
7
6 5
4
3
2 1
CH3-CH2-CH2-CH2-CH2-CH2-CH2-COOH Carboxyl group
Hydrocarbon chain
Octane + acid = Octanoic acid Common name – Caprylic acid
➢ For example, the C18 saturated fatty acid is called octadecanoic acid
because the parent hydrocarbon is octadecane.
➢ A C18 fatty acid with one double bond is called octadecenoic acid;
with two double bonds, octadecadienoic acid; and with three double
bonds, octadecatrienoic acid.
❑The notation 18:0 denotes a C18 fatty acid with no double bonds,
whereas 18:2 signifies that there are two double bonds.
❑ The Carbon atoms are numbered from COOH group as 1. The carbons
adjacent to this are 2,3,4 etc or α, β, γ.
❑ Carboxyl group carbon is C1, next carbon atom is C2/ α-carbon, next is β
and so on.
❑ The position of a double bond is represented by the symbol ∆ followed by
a superscript number counting from carboxyl group end. eg, ∆ 9 indicates a
double bond between carbons 9 and 10 of the fatty acid.
❑ Alternatively, the position of a double bond can be denoted by counting
from the distal end, with the ω- carbon atom (the methyl carbon) as
number 1.
➢ ω9 indicates a double bond on the ninth carbon counting from the ωcarbon.
❑ In animals, additional double bonds are introduced only between the
existing double bond (eg, 9, 6, or 3) and the carboxyl carbon, leading to three
series of fatty acids known as the ω9, ω6, and ω3 families, respectively.
CH3 – CH2 - CH2 - COOH
1
Butyric acid
(Arabic numbers)
4
3
2



(Greek alphabetical numbers)
ω1
ω2
ω3
(Omega numbers)
Polyunsaturated fatty acid of ω6 family
E.g., linoleic acid (18: 2 ; Δ9,12 ) ω6.
12
9
CH3 - (CH2)4 - CH = CH - CH2- CH = CH - (CH2)7 – COOH
In (18: 2 ; Δ9,12 ) ω6 or Δ6.
where, 18= total no of carbon atom, 2= no of double bonds,
(Δ 9,12) OR 9,12= first carbon position of double bonds, starting from
the carboxyl end,
➢ ω6 = first carbon position of double bonds starting from terminal
methyl group (ω,omega carbon)
Poly-unsaturated
Essential Fatty acids
α-Linolenic ALA) EPA DHA
nuts - flaxseed oil soybean and canola
oil- fatty fish (tuna &
salmon)
Omega-3 Fatty acids
Omega-6 Fatty acids
Linoleic (18:2)
Arachidonic (2o:4)
corn oil - sunflower oilsafflower, soybean
meat, eggs
12/14/2023
Dr.Shaymaa Galal lecturer
of Biochemistry
General structure of Fatty Acid:
❑ Fatty
acids are amphipathi molecules composed of a hydrophilic
(polar, ionized) head (formed by the carboxyl group) and a hydrophobic
(non-polar, non-ionized) tail (formed by the hydrocarbon chain).
❑ -The degree of solubility of a fatty acid depends on the length of the
hydrocarbon chain.
H+
CH3 – (CH2)n –COOH
Ionization (at pH:7)
CH3 – (CH2)n –COO-
Classification of fatty acids:
1. According to chain length: short, medium and long
2. According to degree of saturation: saturated & unsaturated
3. According to chain type: branched and cyclic.
4.According to Biological value: essential & non-essential
Classification of fatty acids:
1. According to chain length: short, medium and long
A)Low or short chain fatty acids: Contain 8 carbon atoms or less (from 2-
8) Acetic acid (2 C): CH3-COOH
Butyric (4 C): CH3-CH2-CH2-COOH
B)Medium-chain fatty acids: Contain from 10-12 carbon atoms
C)High or Long chain fatty acids: Contain more than 12 carbon atoms
Palmitic (16 C): CH3-(CH2)14-COOH
Stearic (18 C): CH3-(CH2)16-COOH
Lignoceric (24 C): CH3-(CH2)22COOH
2. According to degree of saturation: saturated & unsaturated
A) Saturated Fatty Acids: They do not contain double bonds
❑ Saturated fatty acids may be envisaged as based on acetic acid
(CH3 —COOH) as the first member of the series in which —
CH2— is progressively added between the terminal CH3 — and —
COOH groups.
❑ Fatty acids in biological systems usually contain an even
number of carbon atoms, typically between 14 and 24. The 16and 18-carbon fatty acids are most common.
❑ The hydrocarbon chain is almost invariably unbranched in
animal fatty acids. A few branched-chain fatty acids have also been
isolated from both plant and animal sources.
Palmitic acid (16 C)
CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH
[ CH3-(CH2)14-COOH ]
Stearic acid (18 C)
CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2 CH2-CH2-CH2-CH2-COOH
[ CH3-(CH2)16-COOH ]
Number of C
atoms
Common Name
Systemic Name
Formula
2
Acetic acid
Ethanoic acid
CH3COOH
4
Butyric acid
Butanoic acid
CH3(CH2)2COOH
6
Caproic acid
Hexanoic acid
CH3(CH2)4COOH
8
Caprylic acid
Octanoic acid
CH3(CH2)6COOH
10
Capric acid
Decanoic acid
CH3(CH2)8COOH
12
Lauric acid
Dodecanoic acid
CH3(CH2)10COOH
14
Myristic acid
Tetradecanoic acid
CH3(CH2)12COOH
16
Palmitic acid
CH3(CH2)14COOH
18
Stearic acid
20
Arachidic acid
Hexadecanoic
acid
Octadecanoic
acid
Eicosanoic acid
22
Behenic acid
DocBoiosaenostriycfoarceiddics
CH3(CH2)16COOH
CH3(CH2)18COOH
C6/H29/2(0C12H) COOH
3 2 20
A) Unsaturated Fatty Acids: They contain one or more double bonds
They are named by adding suffix “enoic”
(1)Monounsaturated (monoethenoid, monoenoic) acids, containing one
double bond.
e.g. Oleic acid (18: 1; 9 )ω9 or Δ9
CH3-(CH2)7-CH = CH-(CH2)7-COOH
In (18: 1; 9 ) ω9 , 18= total no of carbon atom, 1= no of double
bonds, 9= first carbon position of double bonds, starting from the
carboxyl end, ω9/ Δ9 = first carbon position of double bonds
starting from terminal methyl group (ω,omega carbon)
(2) Polyunsaturated (polyethenoid, polyenoic) acids, containing two or
more double bonds. The configuration of the double bonds in most
unsaturated fatty acids is cis. The double bonds in polyunsaturated
fatty acids are separated by at least one methylene group.
Nuts contain high content of PUFA, low saturated fats and high conte
of vitamin E.
e.g. peanuts, almonds and cashews
1. Dienoic fatty acids (contain 2 double bonds) •
e.g. linoleic acid (18: 2 ; 9,12 ) ω6.
12
9
CH3 - (CH2)4 - CH = CH - CH2- CH = CH - (CH2)7 – COOH
2. Trienoic fatty acids (contain 3 double bonds)
e.g. α-Linolenic acid (18: 3; 9,12, 15) ω3
9
15
12
CH3 - CH2 - CH = CH - CH2 - CH = CH - CH2 - CH = CH - (CH2)7 -COOH
CH3 - (CH2 - CH = CH)3 - (CH2)7 - COOH
3. Tetraenoic fatty acids (contain 4 double bonds)
e.g. Arachidonic acid (20: 4; 5, 8, 11, 14) ω6
CH3 - (CH2)3 - (CH2 - CH = CH)4 - (CH2)3 - COOH
Polyunsaturated fatty acid of ω3 & ω6 family
4. According to Biological value: essential & non-essential
Essential Fatty Acids
▪ The Fatty Acids that cannot be synthesized by the body, should be supplied through
diet known as essential fatty acids. They are polyunsaturated fatty acids, linoleic acid
and linolenic acid.
▪ Mammals can synthesize saturated fatty acids (FAs) and monounsaturated FAs,
but they are unable to synthesize FAs containing more than one double bond
because they lack the enzyme system that is responsible for introduction of more
than one double bond.
▪ Arachidonic acid is synthesized in the body from linoleic acid, so it is a nonessential fatty acid.
▪ It is also found in animal fats and peanut oil.
▪ Arachidonic acid becomes essential if its precursor, linoleic acid, is missing in the
Significanceof Essential Fatty Acids
❑ Components of cell membranes, structural elements of
membrane.
❑ Required for brain growth and development gonads.
❑ Precursors for synthesis of Eicosanoids
❑ They have a cardio protective role- Lower serum cholesterol
and increase HDL levels through cholesterol esterification.
➢
Deficiencies of essential polyunsaturated fatty acids
may cause a wide variety of symptoms, including
retarded growth in children, reduced fertility and
pathologic changes in the skin.
Non Essential Fatty Acids
▪ They can be synthesized by mammals, so it is not essential to take
them in diet.
▪ They include saturated fatty acids and mono- unsaturated fatty acids.