BioChemistry of Lipids......... By Shapi.

BIOCHEMISTRY
• BIOCHEMISTRY OF LIPIDS
Dr. Chongo Shapi (Bsc.HB, MBChB)
Medical Doctor
2/26/2024 1
Dr. Chongo Shapi, BSc.HB, MBChB.

STRUCTURAL FEATURES OF
LIPIDS
2/26/2024 Dr. Chongo Shapi, BSc.HB, MBChB. 2

What are lipids?
• The lipids constitute a very important
heterogeneous group of organic substances in
plant and animal tissues, and related either
actually or potentially to the fatty acids.
• Chemically they are various types of esters of
different alcohols.
• In addition to alcohol and fatty acids, some of
the lipids may contain phosphoric acid,
nitrogenous and carbohydrates.

Bloor’s Criteria
• They are insoluble in water.
• Solubility in one or more organic solvents,
such as ether, chloroform, benzene, acetone,
so called fat solvents.
• Some relationship to the fatty acids as esters
either actual or potential.
• Possibility of utilization by living organisms

Biomedical Importance
• Lipids are important dietary constituents and
acts as fuel in the body. In some respects lipid
is even superior to carbohydrates as a raw
material for combustion, since, it yields more
energy per gm.(9,5C/gm as compared to
carbohydrates 4.0C/gm)
• Can be stored in the body in almost unlimited
amount in contrast to carbohydrates.

Biomedical importance cont.
• Some deposits of lipids may exert an
insulating effect in the body, while lipids
around internal organs like kidney, may
provide padding and protect the organs.
• Building materials: Breakdown products of
fats can be utilized for building biological
active materials.

• Lipids supply so called Essential fatty
acids(EFA), which cannot by synthesized in the
body and are essential in the diet for normal
health and growth.
• The nervous system is particularly rich in lipids
especially certain types and are essential for
proper functioning.

• Some vitamins like A, D, E and K are fat
soluble, hence lipids is necessary for these
vitamins.
• Lipoproteins and phospholipids are important
constituents of many natural membranes such
as cell walls and cell organelles like
mitochondrion.
• Lipoproteins are also carriers of tri glycerides,
cholesterol and PL in the body.

CLASSIFICATION OF LIPIDS
I. Simple lipids: Esters of FA with various alcohols
a. Neutral fats (Triacylglycerol, TG): These are triesters of fatty
acids with glycerol.
b. Waxes are ester fatty acids with higher monohydroxy
aliphatic alcohols.
▪ True waxes are esters of higher fatty acids whit cetyl
alcohol (C16H33OH) or other higher straight chain alcohol.
▪ Cholesterol esters are esters of fatty acids whit
cholesterol.
▪ Vit A and Vit D esters are palmitc or stearic acids esters of
Vit A (retinol) or Vit D respectively.

II. Compound lipids: esters of fatty acids containing groups, other than,
and in addition, to an alcohol and fatty acids.
a. Phospholipids: they are substituted fats containing in addition to
fatty acid and glycerol, a phosphoric acid residue, a nitrogenous base
and other substituents.
b. Glycolipids: lipids containing carbohydrate moiety are called
glycolipids. They contain a especial alcohol called sphingosine or
sphingol and nitrogenous base addition to fatty acids but does not
contain phosphoric acid or glycerol.
▪ Cerebrosides
▪ Gangliosides
c. Sulpholipids: lipid characterized by possessing sulphate groups.
d. Aminolipids (proteolipids)
e. Lipoproteins
CLASSIFICATION OF LIPIDS cont.

III. Derived lipids Derivatives obtained by hydrolysis of those given in group I and II, which
still possess the general characteristics of lipids.
a) Fatty acids may be saturated, unsaturated or cyclic.
b) Monoglycerides and diglycerides.
c) Alcohols
▪ Straight chain alcohol are water insoluble alcohol of higher molecular weight obtained
on hydrolysis of waxes.
▪ Cholesterol and other steroids including Vit D .
▪ Alcohols containing the Vit A and certain carotenoids.
▪ Glycerol

IV. Miscellaneous
▪ Aliphatic hydrocarbons.
▪ Carotenoids.
▪ Squalene is a hydrocarbon found in
shark and mammalian liver and in
human sebum.
▪ Vitamins E and K.

DERIVED LIPIDS

APOLAR
FATTY ACIDS
• A fatty acids (FA) may be defined as an
organic acid that occurs in a natural
triglyceride and is a monocarboxylic
acid ranging in chain length from C4 to
about 24 carbon atoms(C4 to C24).
• FA are obtained from hydrolysis of fats.

Fatty Acids

SATURATED FA: Those
which contain no double
bonds.
UNSATURATED FA:
Those which contain
one or more double
bonds.
CH3(CH2)14-COOH
Palmític acid
CH3-(CH 2)5-CH=CH-(CH2)7-COOH
Palmitoleic acid
TYPES OF FATTY ACIDS
Straight chain

(a) Saturated FA: Their formula is
CnH2n+1COOH.
• Having 10 carbons or less number of
carbon atoms called as lower fatty acids,
e.g. acetic acid, butyric acid. Saturated
fatty acids having more than 10 carbon
atoms are called higher fatty acids, e.g.
palmitic acid, stearic acid.
• Milk contains significant amount of lower
fatty acids.

Saturated FA
• Are found in animal
products such as
butter, cheese,
whole milk, ice
cream, cream, fatty
meats and oils such
as coconut, palm
and palm kernel oil.

(b) Unsaturated FA
They are classified further according to degree of
unsaturation.
(1) Monounsaturated FA: they contain one double
bond. CnH2n-1COOH
Example: Oleic acid C17H33COOH is found in nearly
all fats (formula 18:1;9)

Monounsaturated Fats
• In general, are considered to
be relatively healthy.
• Are more vulnerable to lipid
peroxidation (rancidity).
• Some monounsaturated fatty
acids (in the same way as
saturated fats) promote
insulin resistance, whereas
polyunsaturated fatty acids
are protective against insulin
resistance.

Polyunsaturated fatty acids
• Linoleic acid (18C ω-6):
seeds, nuts and the richest
source, common vegetable oils
• Linolenic acid (18C ω-3):
Soybean oil, canola oil, walnuts
and fatty fish
• EPA and DHA (20-22C
ω-3): fatty fish
(salmon, tuna and mackerel)
These are three polynsatured FA of biological importance.

Polyunsaturated fatty acids.
• Linoleic acid series (18C ω-6): It contains 2
double bonds between C9 and C10, and between
C12 and C13.
• Dietary sources: is present in sufficient amounts
in peanut oil, corn oil, cottonseed oil, soybean oil
and egg yolk.

CH3-(CH 2)4-CH=CH-CH2-CH=CH-(CH2)7-COOH
Linoleic acid
18(9,12)
6
Carbon
atoms
number
Double bonds
positions

• Linolenic acid series (18: 3;9,12,15): it contains 3
double bonds between 9 and 10;12 and 13;and
15 and 16.Their general formula is CnH2n-5COOH
• Dietary source: found frequently whit linoleic
acid, but particularly present in linseed oil,
rapeseed oil, soybean oil, fish viscera and liver
oil.

CH3-(CH 2)4-CH=CH-CH2-CH=CH-(CH2)7-COOH
Linolenic acid
18:3(9,12,15)
Carbon
atoms
number Double bonds
number
Double bonds
positions

• Arachidonic acid series ( 20:4;5,8,11,14): it contain
4 double bonds. Their general formula:CnH2n-7COOH
Dietary source: found in small quantities whit linoleic
and linolenic acid but particularly found in peanut oil.
• Also found in animal fats including liver fats.

(c) Branched chain FA: Odd and even carbon branched chain FA occur in animal and plant
lipids, e.g.
• Sebaceous gland
• Branched chain FA is present in certain foods
(d) Substituted FA: In hydroxy FA and methyl FA, one or more of the H atoms have been
replaced by OH group or CH3 group respectively.
(e) Cyclic FA: FA bearing cyclic groups are present in some seeds.
(f) Eicosanoids: These are derived from eicosapolyenoic FA.
TYPES OF FATTY ACIDS CONT

PROSTANOIDS LEUKOTRIENES (LTs)
LIPOXINS (LXs)
Prostaglandins(PGs)
Prostacyclins (PGIs)
Thromboxanes (TXs)
Arachidonic acid
Eicosanoids

Ácido prostanoico (hipotético)
Derivan estructuralmente del:
PROSTAGLANDINS(PGS)

PGG2 PGH2
PGD2
PGE2 PGI2
TxA2
6-ceto-PGF1
PGF2
PROSTANOIDS

ESSENTIAL FA

• Linoleic acid is most important as, arachidonic
acid (AA) can be synthetized from linoleic acid by
a 3 stage reaction by addition of acetyl CoA.
Piridoxal phosphate is necessary for tis
conversion.
• Biologically AA ire synthesized very important as it
is precursor from which prostaglandins and
leukotrienes are synthesized in the body.
Which EFA is important?

Why EFA cannot be synthesized?
• Introduction of additional double bonds in
unsaturated FA is limited to the area between -
COOH group and existing double bond and that it
is not possible to introduce a double bond
between the CH3 group at the opposite end of the
molecule and the first unsaturated linkage.
• This would explain body inability to synthesize an
EFA from oleic acid.

EFA. Biomedical importance
• Structural elements of tissues.
• Structural elements of gonads.
• Synthesis of prostaglandins and other compounds.
• Structural element of mitochondrial membrane.
• Serum level of cholesterol.
• Effect on clotting time.
• Effect on fibrinolytic activity.
• Deficiency of EFA produces fatty liver.
• Linolenic acid is necessary in the diet for optimal vision.

Steroids and sterols
1. The steroids are often found in association whit fat.
2. They may by separated from the fat, after the fat is
saponified, since they occur in unsaponifiable residue.
3. All of the steroids have a similar cycic nucleus resembling
phenanthrene (ring A, B,C) to which a cyclopentane ring
(D) is attached (cyclopentano perhydro-phenantrene
nucleus.
4. Methyl side chains occur typically at positions 10 and 13.
5. A side chain at position 17 is usual.
6. Most important sterol in human body is cholesterol.

Cholesterol
• Only in foods of
animal origin.
– ↑↑↑ brain
– ↑↑ liver and
other organ meat,
egg yolks
– ↑ muscle tissue,
breast milk, dairy
products.

CHOLESTEROL STRUCTURE
• Molecular formula: C27H45OH
• It possesses cyclopentano-perhidrophenantreno
nucleus.
• It has an –OH group at C3.
• It has an unsaturated double bond between C5and
C6.
• It has two CH3 groups at C10 and C13.
• It has an eight carbon side chain attached to C17.

The Structure of cholesterol
CH3
CH3
HO
H3C CH3
CH3
1
A B
C D
2
3
4
5
6
7
8
9
10
11
12
13
14 15
16
17
18
19
20
21
22
23
24
25
26
27

Cholesterol

Properties
• The name cholesterol is derived from de Greek
words meaning solid bile. It occurs as a white or
faintly yellow , almost odourless, pearly leaflets
or granules.
• Insoluble in water, sparingly soluble in alcohol
and soluble in ether, chloroform, hot alcohol,
ethyl acetate and vegetable oils.
• It is not saponificable
• It is melting point is 147 to 150° C.
• Since it has an unsaturated bond, it can take up 2
halogen atoms.

Source
• Exogenous: dietary cholesterol, approximately
0,3 gm/day. Diet rich in cholesterol are butter,
cream, milk, egg yolk, meat, etc. A hen’s egg
weighing 2 oz gives 250 mg cholesterol.
• Endogenous: Synthesized in the body from
acetyl CoA, approximately 1.0 gm/day

Occurrence
• It is widely present in body tissues.
• Cholesterol is found in largest amounts in normal human adults brain
and nervous tissue 2%.
• In the liver about 0.3%,
• Skin 0.3%
• Intestinal mucosa 0.2%,
• Certain endocrine glands,viz. adrenal cortex contain some 10% or
more.
• Corpus luteum is also rich in cholesterol.
• The relatively high content of cholesterol in skin may be related to vit
D formation by UV rays and that in the adrenal gland and gonads to
steroid hormone synthesis.
• Cholesterol is present in blood and bile and usually a major
constituent of gallstones.

Forms of cholesterol
• Cholesterol occurs both in free form and in ester
form, in which it is esterified whit FA at –OH group
at C3 position. The ester form of cholesterol is also
referred as bound form. The various FA, which form
cholesterol esters, are as follows:
• Linoleic acid: 50%
• Oleic acid: 18%
• Palmitic acid: 11%
• Arachidonic acid:5%
• And other FA: 16%

Esterification of cholesterol
• Some cholesterol esters are formed in tissues by
the transfer of acyl groups from acyl CoA to
cholesterol by acyl transferases.
• But most of the plasma cholesterol esters are
produced in the plasma itself by the transfer of an
acyl group from the β position of lecithin
cholesterol acyl transferase (LCAT)
Lecithin + cholesterol→ Lysolecithin+cholesterol
ester LCAT

Obesity
Excessive accumulation of body fat leading to a
body weight in relation to height that is
substantially greater than some accepted
standards (as BMI).

Obesity
Patterns of body
fat distribution

Obesity
• High-fat diets contribute
to weight gain and obesity.
• Fat makes food taste good
and is often unnoticed in
foods.

Obesity
• Obesity is a risk
factors for many
health problems
such as
hypertension,
atherosclerosis,
stroke, heart and
kidney failure.

Heart disease
• High blood
cholesterol is
associated with
atherosclerosis
• Diet could affect
blood cholesterol
levels

Heart disease
• Scientific evidences indicate that:
– High LDL cholesterol levels poses a greater risk than
high total cholesterol.
– Low HDL cholesterol levels are also considered a risk
factor for heart disease, as are high levels of
triglycerides.
– Elevated blood triglycerides levels are associated with
low HDL levels.
– Even with high HDL levels, people are at increased risk
for heart disease when they have elevated
triglyceride levels.

Other sterol of biological importance
• 7-Dehydrocholesterol: It is an important sterol
present in the skin.
• Ergosterol: It is a plant sterol, is called as
Provitamin-D2.
• Stigmasterol and Sitosterol
• Coprosterol (Coprostanol)
• Other important steroids of biomedical
importance: these include the bile acids,
adrenocortical hormones, gonadal hormones, D
vitamins, cardiac glycosides.

SIMPLE LIPIDS

NEUTRAL FATS. TRIGLYCERIDES
• Neutral fats(TG) are triesters of the trihydric
alcohol, glycerol whit various FA. The type
formula for a neutral fat is:
R1,R2,R3 represent
FA chains which
may or may not all
be the same.

Triacyl
glicerides

Physical properties
1. Neutral fats are colorless, odorless and tasteless
substances.
2. Solubility: they are insoluble in water but soluble
in organic fat solvents.
3. Specific gravity: the specific gravity of all fat is less
than 1.0, consequently all fats float in water.

4. Emulsification: emulsification of fat may by
made by shaking vigorously in water and by
emulsifying agents such as gums, soaps and
protein which produce more stable emulsions.
5. Melting point and consistency: the hardness or
consistence of fats is related to their MP glycerides
of lower FA melt at lower temperature than those
of the higher FA, and the unsaturated FA
glycerides at still lower temperature.
Physical properties

Chemical properties
1. Hydrolysis
• Supper heated steam
• By acids or alkalis
• By specific fat splitting enzymes lipases
2. Additive reactions
3. Oxidation
4. Rancidity

LIPASES
• Lipases are enzymes which hydrolyse a TG
yielding FA and glycerol.
• Sites: lipases are found in human body in
following places.
• a)lingual lipase in saliva, b) gastric lipase in
gastric juice, c) pancreatic lipase in
pancreatic juice, d) intestinal lipase in
intestinal epithelial cell, e) adipolytic lipase in
adipose tissue f) serum lipase

COMPOUND LIPIDS

PHOSPHOLIPIDS

Phospholipids: Chemistry and
functions
• Phospholipids are compound lipids, they
contain in addition to FA and glycerol or
other alcohol, a phosphoric acid residue,
nitrogen containing base and other
substituents.

C OH
H
CH2OH
CH2OH
glycerol
glycerol
O P O−
O−
O
H2C
CH
H2C
O
C
R1
O O C
O
R2
phosphatidate
Phosphatidic acid
R1- COOH
R2- COOH
HO - P- OH
OH
O
2 fatty acids Phosphoric acid
Phospholipids

Phospholipids
• Are not a dietary
essential nutrient.
• Most abundant in egg
yolks, liver, soybeans
and peanuts.
• Often lost when foods
are processed, but are
frequently used as food
additives.

Classification of phospholipids. Celmer and
Carter
• Glycerophosphatides: in this glycerol is the
alcohol group, eg. phosphatidyletanolamine,
phosphatidylcholine,phosphatidylserine,
plasmalogens, phosphatidic acid, cardiolipins and
phosphatides.
• Phosphoinositides: in this group, inositol is the
alcohol,e.g. phosphatidyl as inositol(lipositol)
• Phosphosphingosides: alcohol present is
sphingosine (also called sphyngol), an
unsaturated amino alcohol, e.g. sphingomyelin

O P O
O−
O
H2C
CH
H2C
O
C
R1
O O C
O
R2
X
glycerophospholipid
X
Serine
Ethanolamine
Choline
Inositol
PHOSPHOLIPIDS

PHOSPHATIDYL CHOLINE(LECITHIN)
• It distributed is widely an animals in liver, brain,
nerve, tissues, sperm, metabolic and egg-yolk,
having both metabolic and structural functions.
• In plants, particularly abundant in seeds and
sprouts. Lecithin has been prepared synthetically
also. On hydrolysis, lecithin yields:
• a)glycerol, b)FA c) phosphoric acid and d)
nitrogenous base choline.

Glicero
phospholipids

O P O
O−
O
H2C
CH
H2C
O
C
R1
O O C
O
R2
CH2 CH2 N CH3
CH3
CH3
+
phosphatidylcholine
PHOSPHATIDYLCHOLINES (LECITHINS)

OTHER PHOSPHOLIPIDS OF BIOLOGICAL
IMPORTANCE
1. Phosphatidil ethanolamine (Cephalins)
Cephalins are structurally identical whit
lecithins, whit the exception that the base
ethanolamine replaces choline. They occur with
lecithin , particularly rich in brain and nervous
tissues.

2. Phosphatidyl Inositol (Lipositol)
• Inositol is an alcohol a cyclic compound. It
replaces the base choline of lecithin. Inositol
as a constituent of phospholipids was first
discovered in acid fast bacilli.
• Later it was found to occur in brain and
nervous tissues, moderately in soybeans,
and also occurs in plant phospholipids.

3. Phosphatidyl Serine.
Contains aminoacid serine in place of
ethanolamine found in brain and nervous tissues
and small amount in other tissues. Also found in
blood.

H2C
H
C
OH
CH
N+ CH
C
CH2
CH3
H
H3
OH
( )12
sphingosine
H2C
H
C
OH
CH
NH CH
C
CH2
CH3
H
OH
( )12
C
R
O
ceramide
• Are derivatives of SPHINGOSINE,
complex amino alcohol that
present a large hydrocarbon chain,
and polar portion include an amino
group.
SPHINGOLIPIDS
• When a fatty acid is
attached in amide linkage to the
–NH2 on C-2, the resulting
compound is a CERAMIDE

Sphingomyelin
• Has an additional
phosphate residue
with a choline
group attached to
it on the
sphingosine, in
addition to the
fatty acid.

Functions of phospholipids
• Participate in the lipoprotein complexes which are
thought to constitute the matrix of cell walls and
membranes, the myelin sheath, and of such
structures as mitochondria and microsomes.
• Role in enzyme action
• Role in blood coagulation
• Role in lipid absorption in intestine

• Role in transport of lipids from liver
• Role in electron transport.
• Lipotropic action of lecithin
• Membrane phospholipids as source of AA.
• Insulation
• Cofactor
• Role of phosphatidyl inositides metabolite
in Ca2+ dependent hormone action.
Functions of phospholipids cont.

Clinical importance
a) Dipalmityl lecithin (DPL) acts as surfactant and
lowers the surface tension in lung alveoli.
b) Lecithin –sphingomielin ratio in amniotic fluid has
been used for the evaluation of fetal lung maturity.
c) Estimation of lecithin phosphorus in amniotic fluid
has been considered to be clinically more usefull

GLYCOLIPIDS

CEREBROSIDES (GLYCOSPHINGOSIDES)
• Cerebrosides occur in large amounts in the white
matter of brain and in the myelin sheaths of nerve.
They are not found in embryonic brain but develops
as medullation progresses.
• In smoller amounts they appear to be very widely
distributed in animal tissues. In medullated nerves
the concentration of cerebrosides are much higher
than in non-medullated nerve fibres.

GANGLIOSIDES
• Gangliosides have been isolated from ganglion
cells, neuronal bodies and dendrites. The highest
concentrations are found in gray matter of brain.
Gangliosides are the most complex of
glycosphingolipids.
• Structure: On hydrolysis yield the following:
1. A long chain FA
2. Alcohol sphingosine
3. A carbohydrate moiety: glucose and/or galactose,
one molecule of N- acetylgalactosamine, one
molecule of N- actylneuraminic acid (sialic acid)

Types of gangliosides
• Four important types are:
1. GM1
2. GM2
3. GM3
4. GD3

Clinical importance
• The simplest and common ganglioside found
in tissues is GM3, which contains ceramide,
one molecule of glucose, one molecule of
galactose and one molecule of neuraminic
acid.
• GM1 is a more complex ganglioside derived
from GM3 is of considerable biological
interest, as it is now known to be the receptor
in human intestine for cholera toxin.

Biomedical importance
• Gangliosides are mainly components of
membranes.
• The gangliosides, therefore, can serve as
specific membrane binding sites (receptor
sites) for circulating hormones and thereby
influence various biochemical processes in the
cell.

SULPHOLIPIDS
• Lipids material containing sulphur has long been
known to be present in various tissues and has
been found in liver kidney, testes, brains and
certain tumors.
• Most abundant in white matter of brain. Several
types of sulfur containing lipids have been
isolated from brain and other tissues. In general,
they appear to be sulfate esters of glycolipids, the
sulphate group is esterified whit OH of hexose
moiety of the molecule.

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BioChemistry of Lipids......... By Shapi.

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