Basics of Lipid Biochemistry

 Lipids are water insoluble biomolecules that are highly soluble in organic
solvents like chloroform.
 Lipids are heterogeneous group of compounds related to fatty acids and include
fats, oils, waxes and other related substances.
 Lipids are hydrophobic in nature.
 The term ‘lipid’ was first coined by German biochemist, Bioor, in 1943.
 Chemically fats are defined as the esters of glycerol and fatty acids or
triglycerides of fatty acids.
LIPIDS
Dr. Riddhi Datta

 Diverse range of functions in biological systems
 Important constituents of diet because of their high energy value
 Serve as source of fat soluble vitamins and essential fatty acids in natural food stuffs
 Serve as stored form of energy in adipose tissues
 Serve as insulating material in sub-cutaneous tissues and around certain organs
 Lipoproteins are important constituents of biological membranes
 Plays crucial roles as:
 enzyme cofactors,
 electron carriers,
 light absorbing pigments,
 emulsifying agent in digestive tracts,
 hormones and intracellular messengers
 May act as chaperones to help membrane proteins fold.
FUNCTIONS OF LIPIDS
Dr. Riddhi Datta

 The carbons in the fatty acids (mostly –CH2 group) is almost completely
reduced compared to the carbon in other simple biomolecules (sugars,
amino acids, etc.). Therefore, oxidation of fatty acids will yield more
energy (in form of ATP) than any other form of carbon.
 Fatty acids are not hydrated as mono- and polysaccharides and thus can be
packed more closely in storage tissues.
ADVANTAGE OF ENERGY STORAGE AS FATTY ACIDS
Dr. Riddhi Datta

 Fatty acids are hydrocarbon chains of various lengths and degrees of unsaturation
that terminate with carboxyl group.
 Fatty acids which occur in natural fats are usually monocarboxylic.
 They contain an even number of carbon atoms as they are synthesized from
condensation of 2 carbon units.
 These range from 4 to 36 C-atoms.
FATTY ACIDS
 The chain may be saturated (no double bonds)
or unsaturated (contain one or more double
bonds).
 Some fatty acids may have hydroxyl groups in
the chain (hydroxy-fatty acid) and still others
may possess ring structures (cyclic-fatty acids).
Dr. Riddhi Datta

 Alcohols present in lipid molecules commonly include glycerol, cholesterol and
higher alcohols like cetyl alcohol and mericyl alcohol.
 In the structural formula of glycerol, the C-atoms are numbered 1, 2, 3 from any
end. Since C1 and C3 are identical, they are also denoted as α, β and α’.
ALCOHOLS IN LIPID MOLECULES
Dr. Riddhi Datta

 The systematic nomenclature of fatty acids is based on Genevan System under
the instruction of IUPAC.
 The fatty acid is named after the hydrocarbon with the same number of carbon
atoms, the suffix –oic is written in place of the final letter ‘-e’ in the name of the
hydrocarbon.
 The names of the saturated fatty acids end with the suffix –anoic and those of
unsaturated fatty acids with the suffix –enoic.
 The positions of the carbon atoms are denoted by numbering (carboxyl carbon
atom is C1, the adjacent carbon atom is C2 and so on) or by using Greek letters
(C2 is denoted as α-carbon, C3 is denoted as β-carbon and so on)
ε γ δ β α
R-CH2-CH2-CH2-CH2-CH2-COOH
6 5 4 3 2 1
NOMENCLATURE OF FATTY ACIDS
Dr. Riddhi Datta

 A widely used convention is to indicate the carbon atom number followed by the
number and position of double bonds in the case of unsaturated fatty acids
(position of a double bond is indicated by lower number of the two carbon
atoms involved in double bonding).
a. Oleic acid has 18 carbon atoms and a double bond between C9 and C10:
18:1(Δ9)
b. Linoleic acid has 18 carbon atoms and two double bonds between C9 and C10 as
well as between C12 and C13:
18:2(Δ9,12)
 Generally monounsaturated fatty acids have double bonds at C9 and
polyunsaturated fatty acids at C9, C12 and C15.
Arachidonic acid is an exception:
20:4(Δ5,8,11,14)
NOMENCLATURE OF FATTY ACIDS
Dr. Riddhi Datta

 In nearly all naturally occurring unsaturated fatty acids, the double bonds are in
the cis configuration.
 Trans fatty acids are produced by fermentation in the rumen of dairy animals
and are obtained from dairy products and meat.
 They are also produced during hydrogenation of fish or vegetable oils.
 Diets high in trans fatty acids correlate with increased blood levels of LDL
(bad cholesterol) and decreased HDL (good cholesterol).
 French fries, doughnuts, fast foods and cookies tend to be high in trans fatty
acids.
Dr. Riddhi Datta

 Bioor (1943) classified lipids on the basis of their chemical composition:
 Simple lipids or homolipids
 Compound lipids or heterolipids
 Derived lipids
 Conn and Stumpf (1976) traditionally classified lipids into the following
categories:
 Acyl glycerols
 Waxes
 Phospholipids
 Sphingolipids
 Glycolipids
 Terpenoid lipids including carotenoids and steroids
LIPID CLASSIFICATION
Dr. Riddhi Datta

 Simple lipids or homolipids
 Fats and oils (Triglycerides)
 Simple triglycerides
 Mixed triglycerides
 Waxes
 Sperm whale wax
 Bee wax
 Carnauba wax
LIPIDS
 Complex lipids or heterolipids
 Phospholipids (Phosphatids)
 Phosphoglycerides
 Lecithins
 Cephalins
 Plasmalogens
 Phosphoinositides
(Phosphatidyl inositols)
 Phosphosphingosides
(Sphingomyelins)
 Glycolipids (Cerebrosides)
 Kerasin
 Phrenosin
 Nervon
 Oxynervon
 Derived lipids
 Steroids
 C29, C28, C27 steroids
 C24 steroids
 Terpenes
 Monoterpene
 Sesquiterpenes
 Diterpenes
 Triterpenes
 Tetraterpenes
 Polyterpenes
 Carotenoids
 Lycopene
 Carotenes
 Xanthophylls
Dr. Riddhi Datta

LIPID TYPES (ON THE BASIS OF FUNCTION)
Dr. Riddhi Datta

 These are triglycerides or triacylglycerols.
 These are esters of 3 fatty acid molecules with
a trihydroxy alcohol, glycerol.
 A fat is solid at room temperature while oil is
liquid.
 Triglycerides are most abundant among all lipids,
constituting about 98% of total dietary lipids.
 They are major storage components or depot fats
in plant and animal cells but are not normally
found in membranes.
 They are non-polar, hydrophobic molecules
since they contain no electrically charged or
highly polar functional groups.
SIMPLE LIPIDS: FATS AND OILS
(STORAGE LIPIDS)
D-isomer L-isomer
CH2-OOCR1
H-C-OOCR2
CH2-OOCR3
CH2-OOCR1
R2COO-C-H
CH2-OOCR3
Dr. Riddhi Datta

 Triglycerides which contain same kind of fatty acids in all three positions are
called simple triacylglycerols and are named after the fatty acid they contain.
 Simple triacylglycerols of 16:0, 18:0, and 18:1, for example, are tristearin,
tripalmitin, and triolein, respectively.
 Triglycerides which contain two or more different fatty acids are called as mixed
triacylglycerols.
 To name these compounds unambiguously, the name and position of each fatty
acid must be specified.
Dr. Riddhi Datta

 In eukaryotic cells, triacylglycerols form a separate phase of microscopic, oily droplets in the
aqueous cytosol, ser ving as depots of metabolic fuel.
 Adipocytes or fat cells store large amounts of triacylglycerols as fat droplets.
 Triacylglycerols are also stored as oils in the seeds of many types of plants, providing energy
and biosynthetic precursors during seed germination.
 Adipocytes and germinating seeds contain lipases that catalyze the hydrolysis of stored
triacylglycerols, releasing fatty acids for export to sites where they are required as fuel.
 Humans have adipocytes under the skin, in the abdominal cavity, etc.
 Seals, walruses, penguins, and other warm-blooded polar animals are amply padded with
triacylglycerols which provides insulation.
 In hibernating animals, the huge fat reserves accumulated before hibernation serve the dual
purposes of insulation and energy storage.
 In sper m whales, a store of triacylglycerols and waxes (low density) allows the animals to
match the buoyancy of their bodies to that of their surroundings during deep dives in cold
water.
FUNCTIONS OF FATS AND OILS
Dr. Riddhi Datta

 Waxes are esters of fatty acids with high molecular weight monohydroxy alcohols.
 Fatty acids range between C14 and C36 while alcohols range from C16 to C36.
 Melting varies from 60° - 100ºC.
 The term ‘wax’ originated from old English ‘weax’ meaning ‘material of the
honeycomb’.
 Carnauba wax is the hardest known wax. It consists of fatty acids esterified with
tetracosanol [CH3(CH2)22CH2OH] and tetratriacontanol [CH3(CH2)32CH2OH].
 Waxes are unusually inert due to their saturated nature of the hydrocarbon chain.
However, they can be slowly split with hot alcoholic KOH.
SIMPLE LIPIDS: WAXES
(ENERGY STORES AND WATER REPELLENTS)
Dr. Riddhi Datta

 In planktons, the chief storage form of metabolic fuel.
 Certain skin glands of vertebrates secrete waxes to protect hair and skin and
keep it pliable, lubricated, and waterproof.
 Some aquatic birds, secrete waxes from their preen glands to keep their feathers
water-repellent.
 Leaves of many tropical plants are coated with a thick layer of waxes, which
prevents excessive evaporation of water and protects against parasites.
 Biological waxes find a variety of applications in the pharmaceutical, cosmetic,
and other industries.
 Lanolin (from lamb’s wool), beeswax, carnauba wax (from a Brazilian palm tree),
and wax extracted from spermaceti oil (from whales) are widely used in the
manufacture of lotions, ointments, and polishes.
FUNCTIONS OF WAXES
Dr. Riddhi Datta

 Phospholipids are the most abundant membrane lipids.
 They serve primarily as structural components of membranes and are never stored in
large quantities.
 Phospholipids contain phosphorus in the form of phosphoric acid groups. They differ
from triglycerides in possessing usually one hydrophilic polar ‘head’ group and
usually two hydrophobic nonpolar ‘tail’ groups. They are often called polar lipids.
Thus, phospholipids are amphipathic.
 In phospholipids, two of the –OH groups in glycerol are linked to fatty acids while
the third –OH group is linked to phosphoric acid. The phosphate is further linked
to one of a variety of small polar head groups (alcohols).
 Phospholipids can be classified into:
 Phosphoglycerides
 Phosphoinositides
 Phosphosphingosides
COMPOUND LIPIDS: PHOSPHOLIPIDS
(STRUCTURAL LIPIDS)
Dr. Riddhi Datta

 Major phospholipids found in membranes.
 It consists of two fatty acid molecules or ‘tails’ esterified with the first and second
–OH groups of glycerol.
 The third –OH group of glycerol forms ester bond with phosphoric acid. An additional
substituent group is esterified with the phosphoric acid. This is referred to as ‘head
group’ as it is present at one end of the long phosphoglyceride molecule.
 Of the two fatty acid molecules, the one on C1 is saturated (C16-C18) while the one on
C2 is unsaturated (C18-C20).
 C2 of glycerol is asymmetric in nature.
 All phosphoglycerides contain a negative charge on the phosphoric acid at pH 7. In
addition, the head group may also have one or more electrical charges at pH 7.
PHOSPHOGLYCERIDES
Dr. Riddhi Datta

 Phosphoglycerides are of 3 types:
 Lecithins (Phosphatidyl cholines)
 Cephalins (Phosphatidyl ethanolamine and phosphatidyl serine)
 Plasmalogens (Phosphoglyceracetals)
PHOSPHOGLYCERIDES
Dr. Riddhi Datta

 Found in various oil seeds like soybeans and yeasts. In animals, glandular and nervous
tissues are rich in lecithins.
 Required for normal transport and utilization of other lipids in liver. In its absence,
accumulation of lipids occur in the liver to as much as 30% (against 3-4% in normal)
giving rise to a condition called ‘fatty liver’. This may lead to fibrotic changes.
 Lecithins contain two fatty acids esterified with any two –OH groups of glycerol
while the third –OH group is esterified with a phosphoric acid group. The
phosphoric acid group is again linked to a nitrogen base, choline.
LECITHINS (PHOSPHATIDYL CHOLINES)
CH2-OOCR1
R2COO-CH O
CH2-O-P-O-CH2-CH2-N+(CH3)3
O-
Dr. Riddhi Datta

 On complete hydrolysis, lecithins yield a mixture of choline, phosphoric acid,
glycerol and two moles of fatty acids.
 But partial hydrolysis of lecithins by lecithinase (active components of snake
venom) causes removal of one fatty acid to yield lysolecithins.
 When subjected into blood stream (as a result of snake bite), lysolecithins cause
rapid rupture of RBC (hemolysis).
HYDROLYSIS OF LECITHINS
CH2-OOCR1
HO-CH O
O-
Dr. Riddhi Datta

 These are closely associated with lecithins in animal tissues. They are also structurally
similar to lecithins except that the choline is replaced by either ethanolamine or
serine.
 Accordingly, two types of cephalins are recognized:
 Phosphatidyl ethanolamine
 Phosphatidyl serine
 Since the primary amino group is weaker base than the quaternary ammonium group of
choline, the cephalins are more acidic than lecithins. Cephalins are also
comparatively less soluble in alcohol than lecithins.
 Snake venoms containing lecithiase can also split off fatty acids from cephalins leaving
hemolytic lysocephalins.
CEPHALINS
CH2-OOCR1
R2COO-CH O
CH2-O-P-O-CH2-CH2-N+H3
O-
Phosphatidyl ethanolamine
CH2-OOCR1
R2COO-CH O
CH2-O-P-O-CH2-CH-N+H3
O- COO- Phosphatidyl serine
Dr. Riddhi Datta

 Plasmalogens constitute about 10% of phospholipids in brain and muscles. About
half of heart phospholipids is plasmalogens.
 These ether phospholipids are common in membranes of halophilic bacteria because
they are resistane to phospholipases.
 Structurally they are similar to lecithins and cephalins but have one of the fatty
acid chains replaced by an unsaturated ether.
 Since nitrogen base can be choline, ethanolamine or serine, plasmalogens can be of
three types:
 Phosphatidal choline
 Phosphatidal ethanolamine
 Phosphatidal serine
PLASMALOGENS (PHOSPHOGLYCERACETALS)
Dr. Riddhi Datta

CH2-O-CH=CHR1
R2COO-CH O
CH2-O-P-O-CH2-CH-N+H3
O- COO-
Phosphatidal serine
CH2-O-CH=CHR1
R2COO-CH O
CH2-O-P-O-CH2-CH2-N+H3
O-
Phosphatidal ethanolamine
CH2-O-CH=CHR1
R2COO-CH O
O-
Phosphatidal choline
PLASMALOGENS (PHOSPHOGLYCERACETALS)
Dr. Riddhi Datta

 Phosphoinositides have been found to occur in phospholipids of brain tissues
and soybeans. They play an important role in transport process as well as a
signaling intermediate in cells.
 They have a cyclic hexahydroxy alcohol called inositol which replaces the base.
The inositol is present as the stereoisomer, myo-inositol.
 Number of phosphate groups may be one, two or three. Accordingly, mono-, di-
and triphosphoinositides are found.
PHOSPHOINOSITIDES
(PHOSPHATIDYL INOSITOLS)
Dr. Riddhi Datta

 Commonly found in nerve tissues, specially in the myelin sheaths. Absent in
plants and microrganisms.
 In a syndrome called Niemann-Pick disease, the sphingomyelins are stored in the
brain in large quantities.
 They lack glycerol and instead contain sphingosine or a closely related
dihydrosphingosine.
 They are electrically charged molecules and contain phosphocholine as polar
head group.
PHOSPHOSPHINGOSIDES
(SPHINGOMYELINS)
Dr. Riddhi Datta

 In association with proteins, phospholipids form the structural components of
membranes and regulate membrane permeability
 Phospholipids in the mitochondria maintain the conformation of electron transport
chain components and thus cellular respiration
 They participate in the absorption of fats from the intestine
 They are essential for the synthesis of different lipoproteins and thus participate in
transport of lipids
 They prevent accumulation of fats in liver (lipotropic factors)
 They participate in the transport of cholesterol and thus help in the removal of
cholesterol from the body
 They act as surfactants (respiratory distress syndrome)
 Cephalin participate in the blood clotting
 Phosphatidyl inositol is the source of second messenger that are involved in the
action of some hormones.
FUNCTIONS OF PHOSPHOLIPIDS
Dr. Riddhi Datta

 They are important constituents of brain (8% of solid matter).
 They are composed of a hydrophobic region, containing two long hydrocarbon tails
and a polar region which contains one or more sugar residues and no phosphate.
 Glycolipids form self-sealing lipid bilayer that are the basis for all cellular
membranes.
 In Gaucher disease, cerebrosides appear in relatively large amount in liver and
spleen. In Niemann-Pick disease, cerebrosides are present in large quantities in
brain.
GLYCOLIPIDS
(CEREBROSIDES OR GLYCOSPHINGOSIDES
Dr. Riddhi Datta

 Cerebrosides contain a high molecular weight fatty acid, sphingosine and either
galactose or glucose instead of choline but no phosphoric acid. They are
electrically neutral.
 The Acyl-sphingosine part is called ceramide.
 The sphingosine carries galactose by glycosidic linkage on its primary
alcohol group and the fatty acid by amide linkage on its primary amino
group.
GLYCOLIPIDS
(CEREBROSIDES OF GLYCOSPHINGOSIDES
Dr. Riddhi Datta

 On the basis of their fatty acid components, cerebrosides are of the following
types:
 Kerasin: Contains saturated C24 lignoceric acid
 Phrenosin (cerebron): Contains a 2-hydroxy derivative of lignoceric acid, called
cerebronic acid
 Nervon: Contains an unsaturated homologue of lignoceric acid, called nervonic acid
 Oxynervon: Contains a 2-hydroxy derivative of nervonic acid called oxynervonic
acid.
GLYCOLIPIDS
Dr. Riddhi Datta

 Sulfolipid: A glycolipid that contains sulfur as sulfonic acid group in a hexose is
called sulfolipid. It is localized in chloroplasts of plants and chromatophores in
photosynthetic bacteria.
 Sulphatides: These are sulphate ester analogues of phrenosin, abundant in white
matter of brain. Sulfate is present in ester linkage at C3 of galactose part of the
molecule.
 Gangliosides: Found in ganglion cells, parenchymatous tissues of spleen and
erythrocytes. Constitutes 6% of membrane lipids in gray matter in brain. Contains
N-acylsphingosine linked to glucose or galactose. Also contains N-
acetylgalactosamine and N-acetylneuraminic acid.
GLYCOLIPIDS
Dr. Riddhi Datta

 A ‘catch all’ group in Bioor’s classification.
 These are substances derived from simple and complex lipids by hydrolysis.
 They include:
 fatty acids
 alcohols
 mono- and diglycerides
 sterols
 terpenes
 carotenoids.
DERIVED LIPIDS
Dr. Riddhi Datta

 They contain no fatty acid and are non -saponifiable.
 They are derivatives of a fused and fully saturated ring system, called sterane. This system
consists of 3 cyclohexane rings fused in non -linear manner and a terminal cyclopentane
ring.
 Classes of steroids:
 C29, C28 and C27 steroids:
 Cholesterol: Important component of cell membranes and plasma lipoproteins, precursor
of bile acid and various steroid hormones. Molecular formula: C27H46O
 Cholestanol
 Ergosterol
 Lanosterol
 Stigmasterol
 Sitosterol
 C24 steroids or bile acids
DERIVED LIPIDS: STEROIDS
Dr. Riddhi Datta

 Non-saponifiable lipids found in plants.
 These group includes:
 Monoterpenes
 Sesquiterpenes
 Diterpenes
 Phytol
 Triterpenes
 Polyterpenes
DERIVED LIPIDS: TERPENES
Dr. Riddhi Datta

 These are tetraterpenes.
 Exclusively of plant origin
 Non-saponifiable
 They are isoprene derivatives with a high degree of unsaturation
 Example: Lycopene (in tomato), carotene (in carrot), etc.
DERIVED LIPIDS: CAROTENOIDS
Dr. Riddhi Datta

 State: Saturated fatty acids are solid at room temperature while unsaturated fatty
acids are liquid, in general
 Colour, odour and taste: Pure fats are colourless, odourless and bland taste.
 Solubility: Soluble in organic solvent. Longer the fatty acyl chain and fewer the
double bonds, the lower is its solubility in water.
 Specific gravity: Less than 1
 Geometric isomerism: Present
 Emulsification: Found
 Melting point: Depends on the chain length of the constituent fatty acyl chain
and the degree of unsaturation.
PHYSICAL PROPERTIES OF LIPIDS
Dr. Riddhi Datta

 Hydrolysis: Fats are hydrolyzed by enzyme lipase to yield fatty acids and
glycerol.
 Saponification: Hydrolysis of fats by alkali is called saponification which results
in the formation of glycerol and salts of fatty acids (called soaps).
 Hydrogenation: Unsaturated fatty acids react with gaseous hydrogen to yield
saturated fatty acids.
 Halogenation: Unsaturated fatty acids and their esters can take up halogens
(Br2, I2, etc.) at their double bonds at room temperature in acetic acid or
methanol solution. This reaction is the basis of ‘iodine number determination’.
 Oxidation: Unsaturated fatty acids are susceptible to oxidation at their double
bonds.
CHEMICAL PROPERTIES OF LIPIDS
Dr. Riddhi Datta

 Acid number: It is the number of milligrams of KOH required to neutralize the
free fatty acids present in 1 gram of fat. The acid number indicates the quantity of
free fatty acid present in a fat.
 Saponification number: It is the number of milligrams of KOH required to
saponify 1 gram of fat. The saponification number provides information on the
average chain length of the fatty acids in fats.
 Iodine number: It is the number of grams of iodine absorbed by 100 grams of
fat. The iodine number indicates the degree of unsaturation of the fatty acids
present in a fat.
Dr. Riddhi Datta

 Acetyl number: It is the number of milligrams of KOH required to neutralize the
acetic acid obtained by saponification of 1 gram of fat after it has been acetylated.
The acetyl number indicates the number of –OH groups present in fat.
 Rancidity: When lipid rich foods are exposed for too long in air (oxygen), they
may spoil and become rancid. The unpleasant taste and smell associated with
rancidity results from oxidative cleavage of the double bonds in unsaturated fatty
acids, producing aldehydes and carboxylic acids of shorter chain length which are
volatile.
Dr. Riddhi Datta

 Our body can synthesize most of the fatty acids except a few. These fatty acids
must be supplied through diet and are termed as essential fatty acids.
 Example-α-Linolenic acid (ω-3 fatty acid), Linoleic acid (ω-6 fatty acid)
 It is recommended that essential fatty acids make up 3% to 6% of your daily
caloric intake. Of this percentage, you should consume 2 to 4 times more omega-
6 fatty acids than omega-3 fatty acids.
ESSENTIAL FATTY ACIDS
Dr. Riddhi Datta

 Omega-3 sources include:
 Nuts
 Soybeans
 Walnut oil
 Canola oil
 Flaxseed oil
 Cold water fatty fish such as salmon, herring, cod, flounder, tuna, bluefish and shrimp
 Omega-6 sources include:
 Leafy vegetables
 Seeds
 Nuts
 Grains
 Vegetable oils (corn, safflower, soybean, cottonseed, sesame, sunflower)
ESSENTIAL FATTY ACIDS
Dr. Riddhi Datta

 Help with cellular development and the formation of healthy cell membranes.
 Blocks tumour formation and growth of cancer cells
 Assist in the development and function of the brain and nervous system.
 Regulates proper thyroid and adrenal activity.
 Plays a role in thinning your blood, which prevents blood clots, heart attacks and
stroke.
 Regulates blood pressure, immune responses and liver function.
 Deficiency causes skin problems, including eczema, dandruff, split nails and
brittle hair.
 Forms Lipid rafts which affects cellular signalling.
 Acts on DNA, activates or inhibits transcription factors.
ROLES OF ESSENTIAL FATTY ACIDS
Dr. Riddhi Datta

Basics of Lipid Biochemistry

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