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PTT103
BIOCHEMISTRY
LIPID
Pn Khadijah Hanim Abdul Rahman
School of Bioprocess Engineering
Week 5: 8/10/2012
Sem 1, 2012/2013
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

Outline
Lipid Classes
- Fatty acids and their derivatives
- Triacylglycerols
- Wax esters
- Phospholipids
- Sphingolipids
- Isoprenoids
 Membranes
- Membrane structure
- Membrane function

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 and
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 cisconfiguration
 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 point

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, 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.


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) – discuss later
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
-
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 have a single glucose or galactose
at the 1-hydroxy position
- Sulfatides are sulfated cerebrosides
- Gangliosides sphingolipids that possess
oligosaccharide groups, one of which must be
sialic acid

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
molecules that are found largely in
essential oils of plants)
Classified according to number of isoprene
residues they contain :
Monoterpenes (2 isoprene units- 10 Cs)
eg. geraniol in oil of geranium
Sesquiterpenes (3 isoprenes)
eg. Farnesene (part of citronella oilused in soaps and perfumes)
Diterpenes (4 isoprenes)
eg. Phytol, a plant alcohol
- Triterpenes (6 isoprene)
eg. Squalene in shark liver oil, olive oil
- Tetraterpenes (8 isoprene)
eg. Carotenoids, orange pigment
- Polyterpene (Thousands isoprene)
eg. Rubber (3000-6000 isoprene)

-
-
-
Steroids (derivatives of the
hydrocarbon ring system of
cholesterol)
Complex derivatives of triterpenes (6 Cs)
Eukaryotes & some bacteria
Composed of 4 fused rings
Distinguished from each other by placement
of carbon-carbon double bonds and various
constituents (OH, Carbonyl & alkyl groups)
Eg cholesterol, progesterone, testosterone,
estradiol

-
-
-
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.
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
Types of lipoproteins


-
-
-
Chylomicrons- large lipoproteins of extremely low
density.
Transport dietary TAG and cholesteryl esters from
intestine to muscle and adipose tissues.
Very low density lipoproteins (VLDL)- 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.

-
-
High-density lipoprotein (HDL)- 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.

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?
