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PTT103
BIOCHEMISTRY
LIPID
Week 7: 21/10/2013
Sem 1, 2012/2013
Department of Chemical Engineering Technology, UniMAP
[email protected]
Course outcome
Able to differentiate basic structure,
properties, functions and classification of
important biomolecules.
 Content:
- Structure and function of lipids and their
derivatives
- Classification of lipids
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Outline
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Lipid Classes
Fatty acids and their derivatives
Triacylglycerols
Wax esters
Phospholipids
Sphingolipids
Isoprenoids
Introduction
diverse group of biomolecules
 eg. Fats, oils, phospholipids, steroids,
carotenoids- which differ in structure and
function are considered as lipids
 Lipids – Those substances from living
organisms that dissolve in nonpolar solvents
eg. Ether, chloroform, acetone but not in
water.
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Role & function as :
◦ structural components in cell membranes
(e.g phospolipids and sphingolipids)
◦ Fats and oil means to store energy (e.g
triacylglycerols)
◦ chemical signals, vitamins, or pigments,
◦ protective molecules (outer coatings for
cells).
Lipid classes
Lipids may be classified into following
classes:
 Fatty acids and their derivatives
 Triacylglycerols
 Wax esters
 Phospholipids
 Sphingolipids
 Isoprenoids

Fatty acids and their
derivatives
Fatty acids – monocarboxylic acids that
contain hydrocarbon chains of variable
length (12-20 C), R-COOH
 Fatty acids are important components of
several types of lipid molecules
 Occur primarily in
- triacylglycerols
- several types of membrane bound lipid
molecules.

Fatty acids and their derivatives

Naturally occurring fatty acids have an even no of C
atoms that form unbranched chain.

2 types
saturated
(only carbon-carbon single bond)
unsaturated
(one/more double bonds)
- can occur in two isomeric forms; cis/trans
- cis : identical groups are on the same side of a double
bond
- Trans : identical groups are on opposite sides of a double
bond
Cis-isomers : Both R groups are
on the same side of the
carbon-carbon double bond
Trans-isomers : Have R groups
on different sides.
Monounsaturated : 1 double bond
Polyunsaturated : > 1 double bonds
Fatty acid structure
Naturally occurring FA are in cis-configuration
The presence of cis double bond causes ‘kink’ in FA chain
Thus, unsaturated FA do not pack closely together as saturated
FA.
Less energy is required to disrupt the intermolecular forces
between unsaturated FA- lower melting points and liquid in R.T
Examples of fatty acids
number of double bonds.
position of a double bond
Tot number of C
Fatty acid with one double bond are
referred to as monounsaturated
molecules
 When two or more double bonds occur
in FA usually separated by methyl grouppolyunsaturated.

Plants & bacteria synthesize all fatty acids
they need from acetyl-CoA.
 Mammals can synthesize saturated &
some monounsaturated fatty acid. Other
unsaturated FA obtain from dietary
source.
 Nonessential FA – can be synthesized
 Essential FA – eg: linoleic and linolenic
acids are obtained from diet (vege
oils,nuts,seeds)

Linoleic and linolenic acids: membrane
structure, precursors for several
important metabolites.
 Symptoms of low-fat diets – deficient in
essential FA:
 Dermatitis (scally skin)
 Poor wound healing
 Reduced resistant to infection
 Hair loss
 Thrombocytopenis (reduction in no of
platelets)

Triacylglycerols
Ester of glycerol with 3 fatty acids
molecules
 Neutral fats – no charge
 Most contain FA of varying lengths, which
may be saturated, unsaturated or a
combination of both
 Referred as fats or oils depend on FA
composition
 Fats – solid at room temp, contain mostly
saturated FA

Fats – solid at room temp, mostly saturated FA
 Oils – liquid at room temp, high unsaturated FA
 In animals triacylglycerols (fats)
- store energy > efficiently than glycogen:
1. TAGs are hydrophobic, they coalesce into compact,
anhydrous droplets within cells. Adipocyte stores
TAG.
- Glycogen binds to water- the anhydrous TAG store
equivalent amount of energy in about 1-8th of
glycogen vol.
2. TAG are less oxidized than carbohydrate. TAG release
more energy when they are degraded.
 provide insulation at low temp- poor conductor of
heat. Adipose tissue prevent the heat loss.
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In plants triacylglycerols (oils)
- energy reserve in fruits and seeds
- high amounts of unsaturated FA- plant
oils (eg oleic & linoleic) soybean, peanut,
olive
Wax esters
are esters formed from fatty acids and long
chain alcohols
 Nonpolar lipid
 Function – protective coating on leaves, stems,
fruits, skin and fur of animals
 carnauba wax produced by the leaves of
Brazilian wax palm – 32C carboxylic acid &
34C alcohol component.
 Beeswax – 26C carboxylic acid & 30C alcohol
component

Phospholipids
Roles :
1) Structural components of membranes
2) Emulsifying agents
3) Surface active agents (substance that
lowers surface tension of a liquid)
 Amphipathic molecule
 Have hydrophobic and hydrophilic
domains

Hydrophobic domain
- composed of hydrocarbon chains of fatty acids
 Hydrophilic domain (polar head group)
- composed of phosphate & other charged or
polar group
 Suspended in water they spontaneously
rearrange into ordered structures

◦ Hydrophobic group exclude water
◦ Hydrophilic group exposed to water (Next slide)
◦ They form bimolecular layers: (Basis of membrane
structure)
Phospholipid in aqueous solution

2 types phospholipids :

phosphoglycerides – mol contain glycerol,
fatty acids, phosphate, alcohol (eg choline).
Found in cell membrane

Sphingomyelins – contain sphingosine
instead of glycerol, fatty acids, phoshate,
alcohol
(classified as sphingolipid)
Phosphoglycerides
The simplest phosphoglyceridephosphotidic acid (precursor for all
phosphoglyceride molecules).
 Phosphatidic acid is composed of
glycerol-3-phosphate that is esterified
with 2 FAs.

O
O H2C
R
2
CO
O
R
CH
H2C
O
O
P
O
O
X
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Basic Structure of phosphoglyceride
Sphingolipids

Important membrane components of animal
& plant membranes

Contain long-chain amino alcohol (either
sphingosine or phytosphingosine) linked to
fatty acid mol by amide bond

3 subclasses – ceramide (core of
sphingolipid), sphingomyelin (found in
animal cells), glycosphingolipid
Sphingolipid Components

Sphingomyelin
– animal cell membrane: found in greatest
abundance in myelin sheath of nerve cells.
- have a phosphorylcholine or
phosphoethanolamine molecule with an
ester linkage to the 1-hydroxy group of a
ceramide.
Ceramide are also precursors for glycolipids or
refered as glycosphingolipid
- In glycolipids: monosaccharide, disaccharide and
oligosaccharide is attached to ceramide thru Oglycosidic linkage.
- Glycolipids differ from sphingomyelin: contain
no phosphate.
Classes :- Cerebrosides
- Sulfatides
- Gangliosides

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Cerebrosides have a single glucose or galactose (monosaccharide)
at the 1-hydroxy position
Galactocerebrosides: Found in cell membranes of brain.
Sulfatides are sulfated cerebrosides
Gangliosides sphingolipids that possess oligosaccharide groups, one
of which must be sialic acid
Gangliosides 1st isolated from nerve tissue
Role of glycolipids is still unclear. Some may bind to bacterial toxins
to animal cell membranes.
For eg: toxins that cause cholera, tetanus and botulism bind to
glycolipid cell membrane receptors
E. coli, S. pneumoniae and N. gonorrhoeae the causative agents of
urinary tract infections, pneumonia and gonorrhea, respectively.
sulfatides
gangliosides
Isoprenoids

Biomolecules contain repeating 5 carbon
structural units (isoprene units)
isoprene
Biosynthetic pathway begin with
formation of isopentenyl pyrophosphate
from acetyl-CoA
 Consist of terpenes and steroids

terpenes
Enormous group of
biomolecules found in
essential oil of plants
steroids
Derivatives of
hydrocarbon ring
system of cholesterol
Isoprenoids
Terpenes
monoterpenes
sesquiterpenes
Diterpenes
Triterpenes
tetraterpenes
polyterpenes
Composed of two
isoprene units (10
carbons)
Composed of 3 isoprene
units (15 C)
Composed of 4 isoprene
units (20 C)
Composed of 6 isoprene
units (30 C)
Composed of 8 units (40
C)
High molecular weight
molecules composed of
hundreds or thousands
of isoprene units
Eg: Geraniol found in oil
of geranium
Eg: Farnesene found in
citronella oil used in soap
and perfumes making
Eg: phytol- a plant alcohol
Eg: squalene- found in
large quantities in shark
liver oil, olive oil and
yeast
Carotenoids- orange
pigments found in plants
Eg: natural rubber
composed of 3000-6000
isoprene units
Intermediate in the
synthesis of cholesterol
Carotenes- hydrocarbon
member of this group.
Xantrophylls- oxygenated
derivatives of carotenes
Steroids
Steroids
Complex
derivatives of
triterpenes- 6
isoprene units
(30 C)
- Composed of
4 fused rings
Steroids are
distinguished by
the placement
of C-C double
bonds and
various
substituents
(OH, C=O and
alkyl groups)
Found in all
eukaryotes and
small no of
bacteria.
Eg: cholesterol,
progesterone,
testosterone,
estradiol
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Cholesterol
Important mol in animals cell membrane
& precursor for synthesis of all steroid
hormones, vit D & bile salts.
Possesses 2 methyl (C-18 & C-19),
attached to C-13 & C-10 & a double
bond
Has a OH group (sterol)
Cholesterol often stored in the cells as a
fatty acid ester.
The esterification reaction is catalyzed by
the enzyme acyl-CoA acyltransferase.
Cholesterol
Functions:
- Essential component of animal
cell membranes
- Precursor in the synthesis of all
steroid hormones, vit D and bile
salts
Cholesterol
Usually stored as
fatty acids ester
Cholesterol possesses 2 methyl
substituents (C-18 and C-19)
attached to C-13 and C-10 and a
double bond (C-5)
A branched hydrocarbon side chain
attached to C-17
Has a OH group attached to C-3: it’s
a sterol
Animal Steroids
LIPOPROTEINS
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Lipoproteins- describe the protein that is
covalently linked to lipid groups
Commonly found in the blood plasma of
mammals.
Plasma lipoproteins transport lipid molecules
(TAG, phospholipids & cholesterol) thru the
bloodstream from 1 organ to the other.
Protein components of lipoprotein- apoprotein
Lipoproteins are classified according their
density
Classes of lipoproteins
Chylomicrons
High density
lipoproteins
(HDL)
lipoproteins
Low density
lipoproteins
(LDL)
Very low
density
lipoproteins
(VLDL)
Chylomicrons
VLDL
LDL
HDL
•large lipoproteins of extremely low density.
•Transport dietary TAG and cholesteryl esters from intestine to
muscle and adipose tissues.
• synthesized in the liver, transport lipids to tissues.
•As VLDL are transported thru the body, they become depleted of
TAGs and some apoprotein and phospholipids.
•Eventually, the TAG-depleted VLDL remnants are either picked up
by the liver or converted to LDL.
•LDL carry cholesterol to tissues.
•LDL are engulfed by cells after binding to LDL receptors.
•also produced in liver.
•Cholesteryl esters are formed when the plasma enzyme
lecithin:cholestero acyltransferase transfers a FA residue from
lecithin to cholesterol.
•HDL transport these cholesteryl ester to liver.
•Liver can dispose cholesterol, convert most of it to bile salts.
Atheroscelerosis
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Chronic disease in which soft masses/plague
accumulate on the inside of arteries.
During plaque formation- smooth muscle cells,
macrophages and various cell debris built up.
As they are filled with lipid- they take a foam
like appearance.
Eventually, the plaque may calcify and protrude
sufficiently into arterial lumens that blood flow
impeded.
Common consequences of atherosclerosiscoronary artery disease- damages heart muscle.
Most of the cholesterol found in plaque is
obtained by the ingestion of LDL by foam
cells- directly correlated with high risk for
coronary heart disease.
 High plasma HDL- low risk for coronary
artery disease.
 Liver cells are the only cells that possess
HDL receptors.
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Questions
Classify and differentiate lipid classes
 What role do plasma lipoproteins play in
human body? Why do plasma lipoproteins
require a protein component to
accomplish their role?
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