Lipids
What are Lipids?
Lipids are non-polar (hydrophobic) organic
compounds, insoluble in water, soluble in
organic
solvents
(ether,
acetone,
carbontetrachloride).
They contain carbon, hydrogen, and oxygen;
sometimes nitrogen and phosphorus.
In most cases they yield fatty acids on
hydrolysis.
They take
metabolism.
place
in
lipid
and
plant
Fatty acids
Fatty acids (FAs) consist of hydrocarbon chain with a
carboxylic acid at one end  straight-chain organic acids
Most naturally occurring fatty acids have an even
number of carbon atoms
They can be saturated and unsaturated.
Unsaturated fatty acids have lower melting points than
saturated fatty acid.
Fatty acids
Monounsaturated FAs  one double bond
Polyunsaturated FAs many double bonds
Eicosanoids (include prostaglandins,
prostacyclins, thromboxanes)
leukotriens,
Double bonds in fatty acids are usually in the cis
configuration.
Linoleic acid
Linoleic acid is a nutritionally essential fatty acid.
that must be ingested by humans and other animals
because the body requires it but cannot synthesize it.
It is found in large conc. in corn, peanut, soyabean
oils but not in olive oil.
Absence of linoleic acid by infants  weight loss
and ezema.
Classification of lipids according to their structures
Classification of lipids according to their structures
Simple lipids  esters of FAs (FAT, OIL, WAX) [One or two chemical
identities)
Hydrolysis of a simple lipid  Simple lipid + H2Ofatty acid + alcohol
If the alcohol is glycerol (FAT or OIL)
If the alcohol is a monohydric alcohol WAX
Hydrolysis of complex lipids more fatty acids + alcohol +other
compound
Phospholipid + H2O (hydrolysis) FA + alcohol + phosphorus +
nitrogen compound.
Phospholipids phosphoglyceride or phosphosphingoside
Glycolipid + H2O (hydrolysis)  FA +a carbohydrate + sphingosine
Classification of lipids
according to their structures
Precursor lipids compounds resulting
from hydrolysis of simple or complex lipids
(FA, sphingosine)
Derived lipids lipids which are formed
due to the transformation of fatty acids
(Prostaglandins, Fat-soluble vitamins)
Fats and oils
Fats with a melting point below room temperature are called
oils.
Iodine number
The iodine number of a fat or an oil is the
umber of grams of iodine that will react with the
double bond present in 100 g of fat or oil
Higher iodine number higher degree of
unsaturation
Generally iodine number of animal fats < iodine
number of vegetable oils
Iodine number of fats <70
Iodine number of oils > 70
Some uses of lipids in the body
Fats serve as fuel.
Fats serve as reserve supply of food and energy.
Fats are stored in special adipose tissues and
serve as a protector for vital organs.
Fats act as heat insulators.
Some lipids allow rapid propagation of electrical
signals.
Physical properties
White or yellowish solid or liquids
Pure fats and oils are odorless and tasteless. Over a
period of time they become rancid and develop an
unpleasant odor and tatse.
Lighter than water.
When shaken with water  temporarily emulsion.
Emulsion can made permanent by addition of
emulsifying agent such soap.
Fats and oils must be emulsified before they can be
digested.
Chemical reactions
Hydrolysis
3. Enzyme
Saponification
Hydrogenation
In Practice not all double bonds are hydrogenated.
Hydrogenation lowers the iodine number.
Acrolein test: Test for fats or oils which contain glycerol
Glycerol (KHSO4) (heat)Acrolein (strong odor)
Rancidity: unpleasant odor or taste developed when fats
stand at room temperature for a short period of time.
Rancidity is due to hydrolysis and oxidation reactions.
Oxidation of double bonds  short chain aldehydes and
acids bad odor and taste (Antioxidant Vit. E and C.)
Fats
+
Water
in
butter
(in
microorganisms)hydrolysis of fats
disagreeable odor.
presence
of
Butyric acid
Fats and foods containing fats have to be covered and
stored in the refrigerator
Cleansing action of soaps
CH3-(CH2)16-COONa (Sodium stearate)
Non-Polar
Hydrophopic
Polar
Hydrophilic
Mechanical Washing causes
the oil to break down into
small drops
Soap emulsifies then the oil
and prevents it from
coalescing.
Soap acts also as surfactant
 lowers surface tension
Micelle
Detergents
Synthetic compounds used as cleansing agents.
Soaps do not work in hard water  insoluble Ca and Mg
salts
Detergents work also in hard water
Soaps (alkaline); Detergents (neutral)  Detergents can be
used on silks and wool; Sops not.
Detergents: Sodium salts if long chain alcohol sulfates
Example: Sodium laurylsulfate
C12H23OH + H2SO4 C11H23CH2OSO3H + H2O
C11H23CH2OSO3H + NaOH  C11H23CH2OSO3Na + H2O
Complex lipids and cell Membranes: an overview
Some functions of membranes (40-50% lipids; 50-60%
Proteins)
1. Mechanical support.
2. Seperate contents of the cells from the environment
3. Structural support for proteins (pumps; receptors)
Introduction to lipids
Self aggregation of lipids
non-polar end
hydrophobic end)
Polar end
(hydrophilic end)
Biochemistry II
Glycerophospholipids
Glycerophospholipids
(phosphoglycerides), are common
constituents of cellular membranes.
They have a glycerol backbone.
Hydroxyls at C1 & C2 are esterified
to fatty acids.
An ester forms when a
hydroxyl reacts with a
carboxylic acid, with loss
of H2O.
CH2OH
H
C
OH
CH2OH
glycerol
Formation of an ester:
O
R'OH + HO-C-R"
O
R'-O-C-R'' + H2O
Phosphatidate
O
O
R1
C
H2C
O
O
CH
H2C
C
R2
O
O
phosphatidate
P
O
O
In phosphatidate:
 fatty acids are esterified to hydroxyls on C1 & C2
 the C3 hydroxyl is esterified to Pi.
O
O
R1
C
H2C
O
O
CH
H2C
C
R2
O
O
P
O
X
O
glycerophospholipid
In most glycerophospholipids (phosphoglycerides),
Pi is in turn esterified to OH of a polar head group (X):
e.g., serine, choline, ethanolamine, glycerol, or inositol.
The 2 fatty acids tend to be non-identical. They may differ
in length and/or the presence/absence of double bonds.
O
O
R1
C
H2 C
O
O
CH
H2 C
C
R2
O
O
P
O
O
H
OH
OH
H
OH
phosphatidylinositol
OH
H
H
H
H
OH
Phosphatidylinositol, with inositol as polar head group,
is one glycerophospholipid.
In addition to being a membrane lipid,
phosphatidylinositol has roles in cell signaling.
O
O
R1
C
H2C
O
O
CH
H2C
C
R2
O
O
P
CH3
O
CH2
O
CH2
+
N CH3
CH3
phosphatidylcholine
Phosphatidylcholine, with choline as polar head
group, is another glycerophospholipid.
It is a common membrane lipid.
O
Each glycerophospholipid
includes
 a polar region:
glycerol, carbonyl O
of fatty acids, Pi, & the
polar head group (X)
O
R1
 non-polar hydrocarbon
tails of fatty acids (R1, R2).
C
H2C
O
O
CH
H2C
C
R2
O
O
P
O
X
O
glycerophospholipid
polar
"kink" due to
double bond
non-polar
Structure of phospholipids
Sphingolipids
are derivatives of the
lipid sphingosine, which has a long
hydrocarbon tail, and a polar domain that
includes an amino group.
OH
H2C
OH
H
C
CH
H3N+
CH
HC
O

O
P
O
(CH2 )12

sphingosine
O
H2C
OH
H
C
CH
H3N+
CH
HC
(CH2 )12
sphingosine-1-P
CH3
CH3
Sphingosine may be reversibly
phosphorylated to produce the signal
molecule sphingosine-1-phosphate.
Other derivatives of sphingosine are
commonly found as constituents of
biological membranes.
OH
The amino group of sphingosine can
form an amide bond with a fatty acid
carboxyl, to yield a ceramide.
H2C
OH
H
C
CH
H3N+
CH
HC
(CH2 )12
OH
OH
H2C
O
H
C
CH
NH
CH
C
R
ceramide
HC
(CH2 )12
CH3
sphingosine
CH3
In the more complex sphingolipids, a
polar “head group" is connected to
the terminal hydroxyl of the
sphingosine moiety of the ceramide.
Sphingomyelin has
a phosphocholine or
phosphethanolamine
head group.
Sphingomyelins are
common constituent
of
plasma
membranes.
CH3
H3C
+
N
O
H2
C
H2
C
O
CH3
P

O
O
phosphocholine
H2C
sphingosine
Sphingomyelin
OH
H
C
CH
NH
CH
O
C
fatty acid
R
HC
(CH2 )12
CH3
Sphingomyelin, with a phosphocholine head group, is
similar in size and shape to the glycerophospholipid
phosphatidyl choline.
Cholesterol, an
important constituent
of cell membranes,
has a rigid ring system
and a short branched
hydrocarbon tail.
HO
Cholesterol
Cholesterol is largely
hydrophobic.
But it has one polar group,
a hydroxyl, making it
amphipathic.
PDB 1N83
cholesterol
Structural features of cholesterol (Chol)
and cholesteryl esters (Chol-esters)
Cholesterol
Four fused hydrocarbon rings (A, B,
C, and D, called the "steroid nucleus"
C8 branched hydrocarbon chain
attached to C17
Hydroxyl group at C-3
 Double bond between C-5 and C-6
Sterols: Steroids with 8 to 10 C in
sides chain and hydroxyl group at C-3
Cholesterol does not occur in plants
Cholesteryl esters
Most plasma cholesterol is in an
esterified form.
More hydrophobic than Chol
Not in membranes
HO
Cholesterol
Cholesterol
in membrane
Cholesterol inserts into bilayer membranes with its
hydroxyl group oriented toward the aqueous phase &
its hydrophobic ring system adjacent to fatty acid
chains of phospholipids.
The OH group of cholesterol forms hydrogen bonds
with polar phospholipid head groups.
Two strategies by which phase changes of membrane
lipids are avoided:
 Cholesterol is abundant in membranes, such as
plasma membranes, that include many lipids with
long-chain saturated fatty acids.
In the absence of cholesterol, such membranes would
crystallize at physiological temperatures.
 The inner mitochondrial membrane lacks cholesterol,
but includes many phospholipids whose fatty acids
have one or more double bonds, which lower the
melting point to below physiological temperature.
Introduction to lipids
Membrane lipids / Cholesterol
Biochemistry II
Testosterone, the male sex hormone, is produced in the testes.
Estradiol, one of the female sex hormones, is produced in the ovaries and placenta.
Cortisol and aldosterone are hormones synthesized in the cortex of the adrenal
gland; they regulate glucose metabolism and salt excretion.
Prednisolone and prednisone are synthetic steroids used as antiinflammatory agents.
• Anabolic steroids (Athletes)
Testosterone
Increase of body mass, strength
Side effects (men)  liver cancer, impotence
Hypercholesterolemia
Breast growth
Side effects (women) increased amount of
body hair
Voice deepening
Menstrual irregularities
Introduction to lipids
Membrane lipids / Cholesterol
Biochemistry II
Atherosclerosis
Form of ateriosclerosis resulting from the
deposition of lipids, primarily TAGs, and Chol,
from the blood stream
Chol. is the larger threat
We have to reduce lipid intake
Unstaurated fish and vegetable oil 
Loweing of Chol level
Normal Chol level = 200-220 mg/dl
Elevated Chol level should be cotrolled by
diet
In extreme cases  cholesterol lowering
drungs (pravastatin, lovastatin)
Structure Of glycosphingolipids
GM2
Sphingomyelin
Glycosphingolipids differ from sphingomyelin in that they do not
contain phosphate.
The polar head function is provided by a monosaccharide or
oligosaccharide attached directly to the ceramide by an o-glycosidic
bond.
OH
HO
OH
OH
O
HO
Neutral glycosphingolipids
O
O
O
NHA c
OH
O
OH
HO
O
GalNAc- b1,3-Gal- a1,4globo-
O
O
HO
O
OH
HN
(C H 2 ) 1 6 C H 3
O
OH
(C H 2 ) 1 2 C
OH
OH
Lactosylceramide (GalO
O H
HO
HO
O
H N
O H
Glucosylceramide
O H
(C H
O
2 )1 6
C H
(C H
O H
b1,4-Glc- b1,1'-Cer)
O
3
2 )1 2
O
O H
C H
3
HO
H N
(C H
O
O H
Galactosylceramide
2 )1 6
C H
(C H
3
2 )1 2
C H
O H
The simplest neutral (uncharged) glycosphingolipids are the cerebrosides (ceramide +
galactose or ceramide + glucose).
They serves primarily as an intermediate in the synthesis and degradation of the more
complex glycosphingolipids).
The cerebroside are found predominantly in the brain and peripheral nervous tissue.
Ceramide oligosaccharides (or globosides) are produced by attaching additional
monosaccharides (including GalNAc).
3
Functions of the Eicosanoids
Eicosanoids participate in many processes in the body:
Inflammatory response that occurs after infection or
injury with symptoms such as pain, swelling, and fever.
An exaggerated or inappropriate expression of the normal
inflammatory response may occur in individuals who have
allergic or hypersensitivity reactions
Contraction of smooth muscles (particularly in the
intestine and uterus)
Increase in the excretion of water and sodium by the
kidney
Regulation of blood pressure
Regulation of bronchoconstriction and bronchodilation
(modulators)
Biosynthesis of the Eicosanoids
Cyclooxygenase Pathway: Synthesis of the
Prostaglandins and Thromboxanes
1. Synthesis of PGH2
Oxidative cyclization of free arachidonic acid
by prostaglandin endo-peroxide synthase 
PGH2 !!!!
PGH2!!!!  variety of prostaglandins and
thromboxanes
Prostaglandin endoperoxide
activities (COX and peroxidase)
synthase-2
2 isoenzymes (COX1 and COX2) [2 O2
molecules]
COX1: (in most tissues): maintenance of
healthy gastric tissue, renal homeostasis, and
platelet aggregation.
COX2: (inducible in a limited number of
tissues) in response to products of activated
immune and inflammatory cells.
Cyclooxygenase Pathway: Synthesis of the
Prostaglandins and Thromboxanes
2. Inhibition of prostaglandin synthesis
Cortisol (a steroidal anti-inflammatory agent
inhibition of PLA2, COX2 but not COX1.
NSAIDS (nonsteroidal anti-inflammatory
agents (e.g. Aspirin) inhibition of COX1 and
COX2 damage to the stomach and the
kidneys, and impaired clotting of blood, is the
basis of aspirin's toxicity.
Specific inhibitors for COX2 (for example,
celecoxib1) are designed to reduce pathologic
inflammatory processes while maintaining the
physiologic functions of COX2.