Lipids

DEPARTMENT OF VETERINARY BIOCHEMISTRY
SUBMITTED BY ;-
BHAGRAJ GODARA
M.V.Sc 1st year
RAJASTHAN UNIVERSITY OF VETERINARY AND ANIMAL SCIENCES,BIKANER
LIPIDS
SUBMITTED TO ;-
DR ANIL MOOLCHANDANI
ASSOCIATE PROFESSOR
VETY. BIOCHEMISTRY

LIPID
 Lipids are organic compounds formed mainly from alcohol and
fatty acids combined together by ester
 Lipids are insoluble in water, but soluble in fat or organic solvents
(ether, chloroform, benzene, acetone).
 Lipids include fats, oils, waxes and related compounds.
 They are widely distributed in nature both in plants and in
animals.

BIOLOGICAL IMPORTANCE OF LIPIDS :
• They are more palatable and storable to unlimited amount compared
to carbohydrates.
• They have a high-energy value (25% of body needs) and they provide
more energy per gram than carbohydrates and proteins but carbohydrates
are the preferable source of energy.
• Supply the essential fatty acids that cannot be synthesized by the body.
• Supply the body with fat-soluble vitamins (a, d, e and k).
• They are important constituents of the nervous system.
• Tissue fat is an essential constituent of cell membrane and nervous
system. It is mainly phospholipids in nature that are not affected by
starvation.

Function of Lipids
1. They are rich source of energy
2. Protect and insulate internal organs
3. Other type of lipids are found in nerve fibers and in hormones ,
which acts as chemical messenger.
4. Provide polyunsaturated fatty acids.
5. A major function of lipids is to build the cell membranes that
separate the internal contents of the cells from the surrounding
aqueous environment.

Fatty alcohols
• (Glycerol & sphingosine)
•Glycerol:
 A trihydric alcohol (i.E., Containing three OH groups) and has
the popular name glycerin.
 It is synthesized in the body from glucose.

It has the following properties:
• Colorless viscous oily liquid with sweet taste.
• On heating with sulfuric acid or khso4 (dehydration) it gives acrolein that has
a badodor.
• This reaction is used for detection of free glycerol or any compound
containing glycerol.
• It combines with three molecules of nitric acid to form trinitroglycerin (tnt)
that is used as explosive and vasodilator.
• 4-on esterification with fatty acids it gives: monoglyceride or monoacyl-
glycerol: one fatty acid + glycerol.
• Diglyceride or diacyl-glycerol: two fatty acids + glycerol.
• Triglyceride or triacyl-glycerol: three fatty acids + glycerol.
• it has a nutritive value by conversion into glucose and enters in structure of
phospholipids.

Uses of Glycerol :
• pharmaceutical and cosmetic preparations.
• Reduces brain edema in cerebrovascular disease.
• Nitroglycerin is used as vasodilator especially for the coronary arteries,
thus it is used in treatment of angina pectoris.
• explosives manufacturing.
• treatment of glaucoma (increased intraocular pressure)due to its ability
to dehydrate the tissue from its water content.

Sphingosine:
 The alcohol(monohydric) present in sphingolipids.
 Synthesized in the body from serine and palmitic acid.
 It is not positive with acrolein test.

Fatty acids
• It is the simplest type of lipid and are found as
components in more complex lipids.
• It contains a long carbon chain attached to carboxylic
acid group at one end.
• Although the carboxylic acid is hydrophilic, the long
hydrophobic carbon chain makes long-chain fatty acids
insoluble in water.
• Fatty acids have even number of carbon atoms, usually
between 10-20.

Example
• Lauric Acid – a 12-carbon acid found in coconut oil.

Structure of fatty acids
• A fatty acid consists of a hydrophobic hydrocarbon chain with a
terminal carboxylgroup

Classification of fatty acidsClassification of fatty acids
Fatty
acids
saturated unsaturated
monounsaturated polyunsaturated

Fatty acids
• Saturated Fatty Acids such as lauric acid contain only single bonds
between carbons.
• Monounsaturated Fatty Acids have one double bond in the carbon chain.
• Polyunsaturated Fatty Acids have two or more double bonds.
 Appear to raise the level of LDL(“bad”) cholesterol in the bloodstream
 Food sources: meat, poultry skin, whole- milk dairy products, and
the tropicaloils- coconut oil, palm oil, and palm kernel oil.

Polyunsaturated FattyAcids
 Fats that seem to lowertotal cholesterol levels.
 Food sources: many vegetable oils, such as corn
oil, soybean oil and safflower oil.

Physical Properties of Saturated Fatty
Acids
• Saturated fatty acids have:
 Molecules that fit closely together in a
regular pattern
 Strong attractions (dispersion forces)
between fatty acid chains
 High melting points that makes them
solids at roomtemperature.

Classification of Lipids
•Simple lipids ( fats & waxes )
•Complex (compound or conjugated
lipids )
•Derived lipids
•Lipid - associating substances

Simple lipids
• A - Neutral Fats and oils (Triglycerides)
• Definition:
 Neutral- uncharged due to absence of ionizable groups in it.
 most abundant lipids in nature.
 constitute about 98% of the lipids of adipose tissue, 30% of plasma or liver
lipids, less than 10% of erythrocyte lipids.
 They are esters of glycerol with various fatty acids.
• Since the 3 hydroxyl groups of glycerol are esterified, the neutral
fats are also called “Triglycerides”.

Waxes, Fats, and Oils
• A wax is an ester of unsaturated fatty acid and long- chain alcohol,
each containing from 14-30 carbon atoms.
• Bees wax obtained from honey combs and carnauba wax obtained
from palm trees are used to give a protective coating to furniture,
car and floors.
• Jojoba wax is used in making candles and cosmetics such as
lipstick.
• Lanolin, a mixture of waxes obtained from wool, is used in hand and
facial lotions to aid retention of water, which softens the skin.

Fats and Oils: Triacylglycerols
• In the body, fatty acids are stored as fats and oils known as
triacylglycerols.
• These substances, also called triglycerides, are triesters of glycerol
and fatty acids.

Triacylglycerols
• A triacylglycerol is produced by esterfication, a reaction in which the
hydroxylgroups of glycerol form ester bonds with carboxyl groups of
fatty acids.

Triacylglycerols
• A triacylglycerol are the major form of energy storage for animals.
• Animals that hibernate eat large quantities of plants,seeds and nuts
that contain large amount of fats and oils.
• They gain as much 14 Kg a week. As the external temperature drops,
the animal goes into hibernation. The body temperature drops to
nearly freezing and there is a dramatic reduction in cellular activity,
respiration and heart rate.
• Animals who live in extremely cold climates will hibernate for
4-7 months.

Triacylglycerols
• However, most fats and oils are mixed triacyglycerols that contain two
or three different fatty acids.
• For example a mix tricylglycerol might be made from lauric
acid,myristic acid and palmitic acid.

Melting Points of Fats and Oils.
• A fat is a triacylglycerol that is solid at room
temperature, such as fats in meat, whole milk, butter
and cheese. Most fats come from animal sources.
• An oil is a triacylglycerol that is liquid at room
temperature. The most commonly used oils come from
plant sources. Olive oil and peanut oil are
monounsaturated because they contain large amounts
of oleic acid.
• Oils from corn,cotton seed, safflower and sunflower are
polyunsaturated because they contain large amounts of
fatty acids with two or more double bonds.

Diagram of Triacylglycerol with
Unsaturated FattyAcids
Unsaturated
fatty acid chains
with kinks
cannot pack
closely.

Melting Points of Fats and Oils.
• Saturated fatty acids have higher melting points than unsaturated
fatty acids because they pack together more tightly.
• Vegetable oils have low melting points because they have a higher
percentage of unsaturated fatty acids than do animal fats.

Chemical Properties of Triacylglycerols
• The chemical reactions of triacylglycerols are similar to those of
alkenes and esters.
• In hydrogenation, double bonds in unsaturated fatty acids react with
H2 in the presence of a Ni or Pt catalyst.
• In hydrolysis, ester bonds are split by water in the presence of an
acid, a base, or an enzyme.

1.Hydrogenation of Oils
• The hydrogenation of oils
• adds hydrogen (H2) to the carbon atoms of double bonds.
• converts double bonds to single bonds.
• increases the melting point.
• produces solids such as margarine and shortening.

Hydrogenation
(CH2)5CH CH(CH2)7CH3
CH(CH2)7CH3(CH2)5CH
O
C (CH2)5CHCH(CH2)7CH3
O
C
O
C
OCH2
CH2 O
CH O
glyceryl tripalmitoleate
(tripalmitolean)
2 14 3
O
C (CH ) CH
O
2 14 3C (CH ) CH
O
CH2 O C (CH2)14CH3
CH O2
CH O+ 3H2
Ni
glyceryl tripalmitate
(tripalmitin)

Olestra a Fat Substitute
Olestra is
• used in foods as an artificial fat.
• sucrose linked by ester bonds to several long-
chain fatty chains.
• not broken down in the intestinal tract.

2.Hydrolysis
CH O
CH2
CH OH
CH2 OH
OHCH2 O
HO C (CH2)14CH3
H2O
In hydrolysis,
• triacylglycerols split into glycerol and three fatty
acids.
• an acid or enzyme catalyst is required.
O
O C (CH2)14CH3
O
C (CH2)14CH3
O
CH2 O C (CH2)14CH3
H+

3.Saponification and Soap
Saponification
• is the reaction of a fat with a strong base.
• splits triacylglycerols into glycerol and the salts of fatty
acids.
• is the process of forming “soaps” (salts of fatty acids).
• with KOH gives softer soaps.

Saponification
O
C (CH2)14CH3
O
CH O C (CH2)14CH3
CH2O
O
C (CH2)14CH3
CH2O
+ 3NaOH CH OH
CH2 OH
CH OH2
Na+ -O
O
C (CH2)14CH3+
Glyceryl
tripalmitate
Glycerol
3 sodium
palmitate

(CH2)7 COOHCH3 (CH2)4 CH CH CH2 CH CH
Linoleic acid
2 I2
CH CH (CH2)7 COOHCH CH CH2CH3 (CH2)4
I I I I
Stearate-tetra-iodinate
 Neutral fats containing unsaturated fatty acids have the
ability of adding halogens (e.g., hydrogen or
hydrogenation and iodine or iodination) at the double
bonds.
 very important property to determine the degree of
unsaturation of the fat or oil that determines its biological
value
4.Halogenation

5.Oxidation (Rancidity)
 This toxic reaction of triglycerides leads to unpleasant odour or
taste of oils and fats developing after oxidation by oxygen of air,
bacteria, or moisture.
 Also this is the base of the drying oils after exposure to
atmospheric oxygen.Example is linseed oil, which is used in
paints and varnishes manufacturing = RANCID
Definition:
 physico-chemical change
 development of unpleasant odor or taste or abnormal color particularly on
aging
 exposure to atmospheric oxygen, light, moisture, bacterial or fungal
contamination and/or heat.
 Saturated fats resist rancidity more thanunsaturated fats that have
unsaturated double bonds.

Types and causes of rancidity
1. Hydrolytic rancidity
2. Oxidative rancidity
3. Ketonic rancidity
1-Hydrolytic rancidity:
• from slight hydrolysis of the fat by lipase bacterial
contamination leading to the liberation of free fatty
acids and glycerol at high temp and moisture.
• Volatile short-chain fatty acids have unpleasant
odor.

2-Oxidative Rancidity:
 oxidation of fat or oil
 by exposure to oxygen, light and/or heat producing peroxide derivatives
 e.g., peroxides, aldehydes, ketones and dicarboxylic acids that are toxic and have bad odor.
 due to oxidative addition of oxygen at the unsaturated double bond of unsaturated fatty
acid of oils.
3-Ketonic Rancidity:
 due to the contamination with certain fungi such as Aspergillus
niger on fats such as coconut oil
 Ketones, fatty aldehydes, short chain fatty acids and fatty alcohols
are formed.
 Moisture accelerates ketonic rancidity.

1-Iodine number (or value):
 Definition: It is the number of grams of iodine absorbed by 100
grams of fat or oil.
 Uses: It is a measure for the degree of unsaturation of the fat, as a
natural property for it.
 Unsaturated fatty acids absorb iodine at their double bonds,
therefore, as the degree of unsaturation increases iodine number
and hence biological value of the fat increase.
 It is used for identification of the type of fat, detection of
adulteration and determining the biological value of fat.

2-Saponification number (or value):
 Definition: It is the number of milligrams of KOH
required to completely saponify one gram of fat.
 Uses:
 Since each carboxyl group of a fatty acid reacts with one
mole of KOH during saponification, therefore, the
amount of alkali needed to saponify certain weight of fat
depends upon the number of fatty acids present per
weight.
 Thus, fats containing short-chain acids will have more
carboxyl groups per gram than long chain fatty acids and
consume more alkali, i.e., will have higher saponification
number.

3-Acids Number (or value):
 Definition: It is the number of milligrams of KOH required
to neutralize the free fatty acids present in one gram of fat.
 Uses: It is used for detection of hydrolytic rancidity because
it measures the amount of free fatty acids present.

4-Reichert- Meissl Number (or value):
 Definition: It is the number of milliliters of 0.1 NKOH
required to neutralize the water-soluble fatty acids distilled
from 5 grams of fat. Short-chain fatty acid (less than 10
carbons) is distillated by steam.
 Uses: This studies the natural composition of the fat and is
used for detection of fat adulteration.
 Butter that has high percentage of short-chain fatty acids has
highest Reichert-Meissl number compared to margarine.

5-Acetyl Number (or value):
 Definition: It is number of milligrams of KOH needed to neutralize the
acetic acid liberated from hydrolysis of 1 gram of acetylated fat (hydroxy
fat reacted with acetic anhydride).
 Uses: The natural or rancid fat that contains fatty acids with free hydroxyl
groups are converted into acetylated fat by reaction with acetic anhydride.
 Thus, acetyl number is a measure of number of hydroxyl groups present.
 It is used for studying the natural properties of the fat and to detect
adulteration and rancidity.

B-Waxes
 Definition: Waxes are solid simple lipids containing a monohydric alcohol
(with a higher molecular weight than glycerol) esterified to long-chain fatty
acids. Examples of these alcohols are palmitoyl alcohol, cholesterol,
vitamin A or D.
 Properties of waxes: Waxes are insoluble in water, but soluble in fat
solvents and are negative for acrolein test.
 Waxes are not easily hydrolyzed as the fats and are indigestible by lipases
and are very resistant to rancidity.
 Thus they are of no nutritional value.

Type of Waxes:
 - Waxes are widely distributed in nature such as the secretion of certain
insects as bees-wax, protective coatings of the skins and furs of animals
and leaves and fruits of plants. They are classified into true- waxes and
wax-like compounds as follows:
A-True waxes: include:
 Bees-wax is secreted by the honeybees that use it to form the combs. It
is a mixture of waxes with the chief constituent is mericyl palmitate.

Waxes Neutral lipids
1.Digestibility:
2-Type of
alcohol:
Indigestible (not Digestible (hydrolyzed by lipase).
hydrolyzed by lipase).
Long-chain monohydric Glycerol (trihydric) + 3 fatty acids
alcohol + one fatty acid.
3-Type of fatty
acids:
4-Acrolein test:
5-Rancidability:
6-Nature at
room
temperature.
Fatty acid mainly palmitic Long and short chain fatty acids.
or stearic acid.
Negative. Positive.
Never get rancid. Rancidible.
Hard solid. Soft solid or liquid.
7-Saponification Nonsaponifiable. Saponifiable.
8-Nutritive
value:
No nutritive value. Nutritive.
9-Example: Bee & carnuba waxes. Butter and vegetable oils.
Differences between neutral lipids and waxes:

2-Compound Lipids
They are lipids that contain additional substances, e.g., sulfur,
phosphorus, amino group, carbohydrate, or proteins beside fatty
acid and alcohol.
Compound or conjugated lipids are
classified into the following types according to the nature of
the additional group:
Phospholipids
Glycolipids.
Lipoproteins
Sulfolipids and amino lipids.

Phospholipids
• Definition: Phospholipids or phosphatides are compound lipids, which contain
phosphoric acid group in their structure.
• Importance:
• They are present in large amounts in the liver and brain as well as blood.Every
animal and plant cell containsphospholipids. The membranes bounding cells and
subcellular organelles are composed mainly of phospholipids. Thus, the transfer
of substances through these membranes is controlled by properties of
phospholipids.
• They are important components of the lipoprotein coat essential for secretion and
transport of plasma lipoprotein complexes. Thus, they are lipotropic agents that
prevent fatty liver.
• Myelin sheath of nerves is rich withphospholipids.

Glycerophospholipids
Glycerol
Fatty acid
Fatty acid
PO4
Amino
alcohol

Structure: phospholipids are composed of:
Fatty acids (a saturated and an unsaturated fatty acid).
Nitrogenous base (choline, serine, threonine, or ethanolamine).
Phosphoric acid.
Fatty alcohols (glycerol, inositol or sphingosine).
Sources: They are found in all cells (plant and
animal), milk and egg- yolk in the form of lecithins

Classification of Phospholipids
• Are classified into 2 groups according to the type of the alcohol present into
two types:
• A-Glycerophospholipids: They are regarded as derivatives of phosphatidic
acids that are the simplest type of phospholipids and include:
• Phosphatidic acids.
• Lecithins
• Cephalins.
• Plasmalogens.
• Inositides.
• Cardiolipin.
• B-Sphingophospholipids: They contain sphingosine as an alcohol and are
named Sphingomyelins.

A-Glycerophospholipids
1.Phosphatidic acids: They are metabolic intermediates in synthesis of
triglycerides and glycerophospholipids in the body and may have
function as a second messenger. They exist in two forms according to
the position of the phosphate

2-Lecithins:
 Definition : Lecithins are glycerophospholipids that contain
choline as a base beside phosphatidic acid. They exist in 2
forms  - and  - lecithins.
 Lecithins are a common cell constituent obtained from brain ( -
type), egg yolk ( - type), or liver (both types).
 Lecithins are important in the metabolism of fat by the liver.
 Structure: Glycerol is connected at C2 or C3 with a
polyunsaturated fatty acid, at C1 with a saturated fatty acid, at C3
or C2 by phosphate to which the choline base is connected. The
common fatty acids in lecithins are stearic, palmitic, oleic, linoleic,
linolenic, clupandonic or arachidonic acids.

Lysolecithin
• causes hemolysis of RBCs. This partially explains toxic effect of snake
venom,. The venom contains lecithinase, which hydrolyzes the
polyunsaturated fatty converting lecithin into lysolecithin.
Lysolecithins are intermediates in metabolism of phospholipids.

Lung surfactant
• Is a complex of dipalmitoyl-lecithin, sphingomyelin and a group of
apoproteins called apoprotein A, B, C, and D.
• It is produced by type II alveolar cells and
• is anchored to the alveolar surface of type II and I cells.
• It lowers alveolar surface tension and improves gas exchange besides
activating macrophages to kill pathogens.
• In premature babies, this surfactant is deficient and they suffer from
respiratory distress syndrome.
• Glucocorticoids increase the synthesis of the surfactant complex and
promote differentiation of lung cells.

3-Cephalins (or Kephalins):
 Definition:
 They are phosphatidyl- ethanolamine or serine. Cephalins occur in
association with lecithins in tissues and are isolated from the brain
(Kephale = head).
 Structure: Cephalins resemble lecithins in structure except that
choline is replaced by ethanolamine, serine or threonine amino acids.
• Certain cephalins are constituents of the complex mixture of
phospholipids, cholesterol and fat that constitute the lipid component
of the lipoprotein “thromboplastin” which accelerates the clotting of
blood by activation of prothrombin to thrombin in presence of
calcium ions.

4-Plasmalogens:
 Definition: Plasmalogens are found in the cell membrane
phospholipids fraction of brain and muscle (10% of it is
plasmalogens), liver, semen and eggs.
 Structure: Plasmalogens resemble lecithins and cephalins in structure
but differ in the presence of , - unsaturated fatty alcohol rather
than a fatty acid at C1 of the glycerol connected by ether bond.
• At C2 there is an unsaturated long-chain fatty acid, however, it may be
a very short-chain fatty acid

5-Inositides:
They are phosphatidyl inositol.
 Structure: They are similar to lecithins or cephalins but they have the cyclic
sugar alcohol, inositol as the base. They are formed of glycerol, one saturated
fatty acid, one unsaturated fatty acid, phosphoric acid and inositol
 Source: Brain tissues.
 Function: Phosphatidyl inositol is a major component of cell membrane
phospholipids particularly at the inner leaflet of it.
• They play a major role as second messengers during signal transduction
for certain hormone..
 On hydrolysis by phospholipase C, phosphatidyl-inositol-4,5-diphosphate
produces diacyl-glycerol and inositol- triphosphate both act to liberate calcium
from its intracellular stores to mediate the hormone effects.

6-Cardiolipins:
 Definition: They are diphosphatidyl- glycerol. They are found in the
inner membrane of mitochondria initially isolated from heart muscle
(cardio). It is formed of 3 molecules of glycerol, 4 fatty acids and 2
phosphate groups.
 Function: Used in serological diagnosis of autoimmunity
diseases.

B-Sphingophospholipids
• 1-Sphingomyelins
 Definition: Sphingomyelins are found in large amounts in brain and
nerves and in smaller amounts in lung, spleen, kidney, liver and
blood.
 Structure: Sphingomyelins differ from lecithins and cephalins in that
they contain sphingosine as the alcohol instead of glycerol, they contain
two nitrogenous bases: sphingosine itself and choline.
 Thus, sphingomyelins contain sphingosine base, one long-chain fatty
acid, choline and phosphoric acid.
 To the amino group of sphingosine the fatty acid is attached by an amide
linkage.

Ceramide
 Ceramide This part of sphingomyelin in which the
amino group of sphingosine is attached to the fatty
acid by an amide linkage.
 Ceramides have been found in the free state in the
spleen, liver and red cells.

B-Glycolipids
• Definition: They are lipids that contain carbohydrate residues with
sphingosine as the alcohol and a very long-chain fatty acid (24 carbon series).
• They are present in cerebral tissue, therefore are called cerebrosides
• Classification: According to the number and nature of the carbohydrate
residue(s) present in the glycolipids the following are
• Cerebrosides. They have one galactose molecule (galactosides).
• Sulfatides. They are cerebrosides with sulfate on the sugar (sulfated
cerebrosides).
• Gangliosides. They have several sugar and sugaramine residues.

1-Cerebrosides:
• Occurrence: They occur in myelin sheath of nerves and white matter
of the brain tissues and cellular membranes.They are important for
nerve conductance.
• Structure: They contain sugar, usually  -galactoseand may be glucose
or lactose, sphingosine and fatty acid, but no phosphoric acid.

• Types: According to the type of fattyacid and carbohydrate present,
there are 4 different types of cerebrosides isolated from the white
matter of cerebrum and in myelin sheaths of nerves. Rabbit
cerebrosides contain stearic acid.
• Kerasin contains lignoceric acid (24carbons) and galactose.
• Cerebron (Phrenosin) contains cerebronic acid (2-hydroxylignoceric
acid) and galactose.
• Nervon contains nervonic acid(unsaturated lignoceric acid at C15) and
galactose.
• Oxynervon contains oxynervonic acid (2-hydroxynervonic acid) and
galactose.

2-Sulfatides:
• They are sulfate esters of kerasin or phrenosin in which the sulfate
group is usually attached to the –OH group of C3 or C6 of galactose.
Sulfatides are usually present in the brain, liver, muscles and testes.

3-Gangliosides:
• They are more complex glycolipids that occur in the gray matter of
the brain, ganglion cells, and RBCs. They transfer biogenic amines
across the cell membrane and act as a cell membrane receptor.
• Gangliosides contain sialic acid (N-acetylneuraminic acid), ceramide
(sphingosine + fatty acid of 18-24 carbon atom length), 3 molecules of
hexoses (1 glucose + 2 galactose) and hexosamine.

C-Lipoproteins
• Definition: Lipoproteins are lipids combined with proteins in the tissues.
The lipid component is phospholipid, cholesterol or triglycerides.
The holding bonds are secondary bonds.
• They include: Structural lipoproteins: These are widely distributed in tissues
being present in cellular and subcellular membranes. In lung tissues acting
as a surfactant in a complex of a protein and lecithin. In the eye, rhodopsin
of rods is a lipoprotein complex.
• Transport lipoproteins:
• These are the forms present in blood plasma. They are composed of a
protein called apolipoprotein and different types of lipids. (Cholesterol,
cholesterol esters, phospholipids and triglycerides). As the
• lipid content increases, the density of plasma lipoproteins decreases

Plasma lipoproteins can be separated by two methods
• Ultra-centrifugation: Using the rate of floatation in sodium chloride
solution leading to their sequential separation into chylomicrons, very
low density lipoproteins (VLDL or pre-  -lipoproteins), low density
lipoproteins (LDL or  - lipoproteins), high density lipoproteins
(HDL or  -lipoproteins) and albumin-free fatty acids complex.
• Electrophoresis: is the migration of charged particles in an electric
field either to the anode or to the cathode.

• a) Chylomicrons: They have the largest diameter and the least
density. They contain 1-2% protein only and 98-99% fat. The main
• lipid fraction is triglycerides absorbed from the intestine and they
contain small amounts of the absorbed cholesterol and phospholipids.
b)Very low-density lipoproteins (VLDL) or pre-  -lipoproteins:
Their diameter is smaller than chylomicrons. They contain about 7-10%
protein and 90-93% lipid. The lipid content is mainly triglycerides formed
in the liver. They contain phospholipid and cholesterol more than
chylomicrons.
c)Low-density lipoproteins (LDL) or  - lipoproteins: They contain
10-20% proteins in the form of apolipoprotein B. Their lipid
content varies from 80-90%. They contain about 60% of total blood
cholesterol and 40% of total blood phospholipids. As their percentage
increases, the liability to atherosclerosis increases.

d)High-density lipoproteins (HDL) or  - Lipoproteins: They contain
35-55% proteins in the form of apolipoprotein A. They contain 45-
65% lipids formed of cholesterol (40% of total blood content) and
phospholipids (60% of total blood content). They act as cholesterol
scavengers, as their percentage increases, the liability to
atherosclerosis decreases. They are higher in females than in males.
Due to their high protein content they possess the highest density.
e)Albumin-free fatty acids complex: It is a proteolipid complex with
99% protein content associated with long-chain free fatty acids for
transporting them.

• Steroids: Cholesterol and
Steroid Hormones
C H 3
C H 3
C H 3
C H 3
H O
C H 3

Steroid Nucleus
A steroid nucleus consists of
• 3 cyclohexane rings.
• 1 cyclopentane ring.
• no fatty acids.
steroid nucleus

Cholesterol in the Body
Cholesterol
• is obtained from meats,
milk, and eggs.
• is synthesized in the liver.
• is needed for cell
membranes, brain and
nerve tissue, steroid
hormones, and vitamin D.
• clogs arteries when high
levels form plaque.
A normal, open
artery.
An artery clogged
by cholesterol
plaque

Lipoproteins
Lipoproteins
• combine lipids
with proteins
and
phospholipids.
• are soluble in
water because
the surface
consists of polar
lipids.

Types of Lipoproteins
Lipoproteins
• differ in density, composition, and function.
• include low-density lipoproteins (LDLs) and high-
density lipoproteins (HDLs).

Steroid Hormones
Steroid hormones are
• chemical messengers in cells.
• sex hormones.
- androgens in males (testosterone)
- estrogens in females (estradiol)
• Adrenocortical hormones from adrenal glands.
- mineralocorticoids (electrolyte balance)
- glucocorticoids (regulate glucose level)

Steroid Hormones
Steroid hormones
• are produced from
cholesterol.
• include sex hormones
such as androgens
(testosterone) in
males and estrogens
(estradiol) in females.

Anabolic Steroids
Anabolic steroids
• are derivatives of testosterone.
• are used illegally to increase muscle mass.
• have side effects including fluid retention, hair growth, sleep
disturbance, and liver damage.

Adrenal Corticosteroids
Steroid hormones called adrenal corticosteroids
• are produced by the adrenal glands located on the top of each kidney.
• include aldosterone, which regulates electrolytes and water balance
by the kidneys.
• include cortisone, a glucocorticoid, which increases blood glucose
level and stimulates the synthesis of glycogen in the liver.

Cell Membranes
Cell membranes
• separate cellular contents from the external
environment.
• consist of a lipid bilayer made of two rows of
phospholipids.
• have an inner portion made of the nonpolar tails of
phospholipids with the polar heads at the outer and inner
surfaces.

Fluid Mosaic Model of Cell Membranes
The lipid bilayer
• contains proteins, carbohydrates, and cholesterol.
• has unsaturated fatty acids that make cell
membranes fluid-like rather than rigid.
• has proteins and carbohydrates on the surface that
communicate with hormones and neurotransmitters.

Fluid Mosaic Model of Cell Membranes

Transport Through Cell Membranes
• The transport of substances through cell membranes involves
•simple diffusion (passive transport), which moves particles
from a higher to a lower concentration.
•facilitated transport, which uses protein channels to
increase the rate of diffusion.
•active transport, which moves ions against a
concentration gradient.

Transport Pathways Through Cell Membranes

Lipids

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