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Chemistry of Lipids
1. LIPIDS
DR IFAT ARA BEGUM
ASSISTANT PROFESSOR
DEPT OF
BIOCHEMISTRY
DHAKA MEDICAL
COLLEGE DHAKA
2. DEFINITIONDEFINITION
Lipids are a heterogeneous group
of compounds, including fats, oils
, steroids, waxes and related
compounds, that are related more
by their physical properties than
by their chemical properties
They have the common property
of being relatively insoluble in
water & soluble in non-polar
solvents such as ether and
chloroform
3. CONTDCONTD
They are not polymeric
substances like proteins,
polysaccharides & nucleic acids
Building block of most of the
lipids: Fatty acid
Lipids that lack fatty acids:
Cholesterol
4. Biological Importance/
Functions of Lipids
Biological Importance/
Functions of Lipids
Includes biological importance /
functions of:
i. Neutral fat/ Triglyceride (TG)/
Triacylglycerol (TAG)
ii. Phospholipid
iii.Glycolipid
iv.Cholesterol
5. Function (Contd)Function (Contd)
Source of energy
Storage form of energy
Provides EFA & helps in absorption
of fat soluble vitamins
Structural component of bio-
membranes & provides
arachidonic acid for synthesis of
eicosanoids
Provides shape and contour of
body
Serve as mechanical cushion for
some internal organs
6. CONTDCONTD
Serves as a thermal insulator in
subcutaneous tissues & around
certain organs
Nonpolar lipids act as electrical
insulators allowing rapid
propagation of depolarization
waves along myelinated nerves
Synthesis of steroid hormones,
bile acids & vitamin D
Helps in coagulation
7. CONTDCONTD
Acts as surfactant to prevent
collapsing tendency of alveoli
Improve the palatability of food
Lipoproteins (combination of
lipids and proteins) serve as the
mean of transporting lipids in
blood
8. IMPORTANCE OF
KNOWLEDGE OF LIPID
BIOCHEMISTRY
IMPORTANCE OF
KNOWLEDGE OF LIPID
BIOCHEMISTRY
To understand :
many important biochemical
areas like obesity, DM,
atherosclerosis, fatty liver, lipid
storage diseases etc
The role of various PUFA in
nutrition and health
12. WaxesWaxes
Esters of fatty acids with higher
MW monohydric alcohols
Fatty acids : usually long chain
(>16C)
Examples: Cholesterol ester,
retinol ester etc
13. 2.COMPLEX LIPIDS2.COMPLEX LIPIDS
Esters of fatty acids containing
groups in addition to an alcohol &
a fatty acid
Includes:
Phospholipids
Glycolipids (glycosphingolipids)
Other complex lipids (like
sulfolipids, aminolipids &
lipoproteins)
14. CONTDCONTD
A) Phospholipids:
Contains a phosphoric acid
residue in addition to fatty acid
and an alcohol
Frequently have nitrogen
containing bases & other
substituents
Example:
i. Glycerophospholipid (alcohol:
glycerol)
ii.Sphingophospholipid (alcohol:
16. 3.PRECURSOR &
DERIVED LIPIDS
3.PRECURSOR &
DERIVED LIPIDS
Derivatives obtained by
hydrolysis of simple & complex
lipids which still possess the
general characteristics of lipids
Includes fatty acids, glycerol,
steroids, other alcohols, fatty
aldehydes, ketone bodies,
hydrocarbons, lipid soluble
vitamins and hormones
17. Remember: Neutral lipidsRemember: Neutral lipids
They are uncharged at normal
body pH
Includes:
TAG
Cholesterol & cholesterol esters
Mono/di- glycerides
18. CLASSIFICATION OF
LIPIDS BASED ON
POLARITY
CLASSIFICATION OF
LIPIDS BASED ON
POLARITY
1. Non polar lipids
2. Polar / Amphipathic lipids
19. 1.NON POLAR LIPIDS1.NON POLAR LIPIDS
Hydrophobic
Water insoluble
Includes TAG, cholesterol ester,
vitamin D ester etc
20. 2. POLAR /
AMPHIPATHIC LIPIDS
2. POLAR /
AMPHIPATHIC LIPIDS
Lipids having both polar
(hydrophilic)& non polar
(hydrophobic) groups
Show limited degree of water
solubility due to the presence of
hydrophilic group
30. ContdContd
i. Simple TAG: If 3 fatty acids are of
same type
ii. Mixed TAG: If 3 fatty acids are of
different types. It predominates
in nature
31. ContdContd
Neutral fat of plant source : has
more unsaturated FA
Neutral fat of animal source : has
more saturated FA
Fats in liquid state are called oil
32. Fat vs. OilFat vs. Oil
FAT OIL
Solid at room
temperature
Liquid at room
temperature
Has more long
chain fatty
acids
Has relatively
short length of
fatty acids
Has more
saturated fatty
acids
Has more
unsaturated fatty
acids
33. Properties of fatProperties of fat
Physical properties:
Neutral, colorless, odorless,
tasteless
Water insoluble but soluble in
fat solvents
Specific gravity: <1 (floats in
water)
34. ContdContd
Oils are liquids at 20 degree C,
they contain higher proportion
of unsaturated fatty acids
Fats are solid at room
temperature and contain
saturated long chain fatty acids
Makes emulsion in water
36. ContdContd
iii) Rancidity:
Development of bad odor & taste of
fat & oil
Occurs due to exposure of fat/oil to
high temp, oxygen,
moisture/humidity, light , metals
Hydrolytic rancidity: Partial
hydrolysis of TG due to traces of
lipases present in the given fat
37. ContdContd
Oxidative rancidity: Partial oxidation
of UFA with the resultant formation
of epoxides and peroxides by free
radicals
Products of rancidity: Toxic (food
poisoning, cancer)
Rancidity destroys Polyunsaturated
EFA & fat soluble vitamins
Preserving the fats with antioxidants
can prevent rancidity
38. ContdContd
iv) Peroxidation: Auto oxidation in
vivo produces lipid peroxides & free
radicals
v) Hydrogenation & hardening:
UFA of fat can absorb hydrogen
& turns in to saturated FA,
which elevates the melting point
of fat, so fat remains hard at
room temperature
39. Functions of fat/TAGFunctions of fat/TAG
Dietary source of energy
Storage form of energy
Add taste & palatability to food
Provides EFA
Helps in absorption of fat
soluble vitamins
40. ContdContd
Acts as:
Thermal/electrical insulator
Mechanical cushion around
internal organ to protect them
from mechanical injury
Cosmetic effect: Gives shape &
contour to body
44. CONTDCONTD
>90% of FA in human body have
even no. of C atoms (14 to 24)
<5% contains odd no. of C atoms
45. FA occurs in body in 2
forms
FA occurs in body in 2
forms
i. As esters in natural fat & oils
ii. In unesterified form as FFA (a
transport form in plasma)
46. Distribution of total plasma
FA
Distribution of total plasma
FA
45% found with TAG
35% with phospholipids
15% with cholesterol esters
5% as free fatty acid (FFA)
47. Numbering of carbon atom
in FA chain
Numbering of carbon atom
in FA chain
Carbon atoms are numbered from
the carboxyl carbon ( carbon no.
1)
Carbon atoms adjacent to
carboxyl carbon (no. 2, 3 & 4) are
also known as the α, β & γ
carbons, respectively
Terminal methyl carbon is ω or n
carbons
50. Classification of FAClassification of FA
May be classified in different ways-
On the basis of total no. of C (i.e.
length of hydrocarbon chain)
On the basis of presence/absence of
double bond in hydrocarbon chain
(i.e. saturation of C)
Nutritional classification
51. Classification on basis of
length of hydrocarbon
chain / no. of C atom
Classification on basis of
length of hydrocarbon
chain / no. of C atom
i. Short chain FA: 2-6 C atoms
ii. Medium chain FA: 8-14 C atoms
iii. Long chain FA: 16-18 C atoms
iv.Very long chain FA: With 20 or
more C atoms
52. Influence of chain length of
FA
Influence of chain length of
FA
Water solubility decreases as
the chain length increases
Melting point increases as the
chain length increases
53. Classification on basis of
saturation of carbon
Classification on basis of
saturation of carbon
54. Saturated Fatty AcidSaturated Fatty Acid
Do not contain any double bond in
their hydrocarbon chain
Represent 50% of body fatty acid pool
The hydrocarbon chains in
saturated fatty acids are fairly
straight and can pack closely
together, making saturated fats
solid at room temperature
56. Unsaturated Fatty AcidUnsaturated Fatty Acid
Contain 1/more double bond in their
hydrocarbon chain
Represent 50% of body FA pool
2 types: MUFA & PUFA
58. ContdContd
b) PUFA:
Has ≥2 double bond
Found in vegetable oil like soyabean
oil, mustard oil, etc (except coconut
oil & palm oil)
Also found in fish oil
e.g. EFA (linoleic, linolenic &
arachidonic acid)
59.
60. Influence of unsaturation
of FA
Influence of unsaturation
of FA
Double bonds in the
hydrocarbon chain causes
bends or kinks in the shape of
the molecule.
As a result, unsaturated fats
can‘t pack closely together,
making them liquid at room
temperature
Melting point decreases as the
degree of unsaturation (no. of
61. NUMBERING SYSTEM FOR
UNSATURATED FATTY ACID
NUMBERING SYSTEM FOR
UNSATURATED FATTY ACID
Delta numbering system: Here C
atoms are numbered starting
from –COOH group. Example:
Oleic acid: 18:1;9 (18-C FA with 1
double bond placed between C-9
&10)
Omega (ω) numbering system:
Here C atoms are numbered starting
from ω carbon end of chain.
Example: Linoleic acid is called ω6-
FA, as the double bond closest to ω
end begins at 6th
carbon counted
62. CIS AND TRANS ISOMERS
IN UFA
CIS AND TRANS ISOMERS
IN UFA
Depends on orientation of
radicals (H) around the axis of
double bond
Cis- If the radicals are on the
same side of the double bond. UFA
are nearly always in cis- form.
Trans- If the radicals are on the
opposite side
63.
64. Nutritional
classification of FA
Nutritional
classification of FA
a) Non-essential FA (NEFA):
FA that body can synthesize
Palmitic acid, Stearic acid etc
b) Essential FA (EFA):
PUFA that body can’t synthesize
So, these must be supplied in diet
65. Functions of fatty acidFunctions of fatty acid
Acts as metabolic fuel
Takes part in synthesis of PL,
glycolipids & cholesterol esters
FA derivatives serve as
hormones & intracellular
messengers (e.g. PG)
67. IntroductionIntroduction
These are PUFA which are not
produced in human body, so, must be
supplied in diet
Includes :
Linolenic acid (18 C omega-3
fatty acid with 3 double bonds)
Linoleic acid (18 C omega-6 fatty
acid with 2 double bonds)
68.
69. ContdContd
Arachidonic acid :
20 C omega 6 fatty acid with 4 double
bonds
Is not essential if diet contains
sufficient linoleic acid. Because,
linoleic acid in human body can be
converted to arachidonic acid to some
extent
May be termed as “semi essential” FA
70. Source of EFASource of EFA
Vegetable oil (except coconut oil
& palm oil)
Fish oil (Rich in linolenic acid)
Cod liver oil
Egg yolk (Source of linoleic acid)
71. Importance of EFAImportance of EFA
Precursor of eicosanoids
Component of biological
membrane
Anti-atherogenic/ cardio
protective role: It reduces
plasma cholesterol by increasing
excretion of cholesterol in bile &
oxidation of cholesterol to bile
acid, thus reduces the risk of
atherosclerosis & coronary
artery disease
72. ContdContd
Required for brain growth &
development
Essential for reproduction
Helps in vision
Formation of lipoproteins
Synthesis of steroid hormones
Supports oxidative
phosphorylation in respiratory
chain
Prevents fatty liver formation
73. Deficiency manifestations of
EFA
Deficiency manifestations of
EFA
Retarded growth
Reduced fertility
Pathologic change in skin:
dermatitis etc
Degenerative changes in arterial
wall
Impaired gonadal functions &
reproductive failure
Fatty liver
Poor wound healing & hair loss
Faulty vision
76. Has 27 C atoms
Has an -OH group at C3
A double bond between C5and C6
Two- CH3 groups at C10and C13
An eight carbon side chain
attached to C17
77. ContdContd
Occurs as free form or in ester
form (hydroxyl group on C-3
position is esterified with a long
chain FA)
Both forms are transported in
lipoproteins
78. Functions/ biological
importance of cholesterol
Functions/ biological
importance of cholesterol
Constituent of biological
membrane
Precursor of steroid hormones,
bile acid & vitamin D
Disadvantage : High plasma level
of cholesterol is associated with
atherosclerotic disorders (stroke,
coronary artery disease)
79. “All sterols are steroids but
all steroids are not sterols”
“All sterols are steroids but
all steroids are not sterols”
Steroid substances: Steroid
nucleus + one oxygen atom at C-3
position of nucleus. Example:
Aldosterone, Testosterone etc
Sterol compounds: Steroid
nucleus + one hydroxyl group at
C-3 position of nucleus. Example:
Cholesterol, Bile acid, Vitamin D
etc
81. IntroductionIntroduction
Complex lipids
Esters of FA with alcohol
attached with phosphoric acid
with or without nitrogen bases
If the alcohol is glycerol:
Glycerophospholipid
If the alcohol is sphingosine:
Sphingophospholipid
82.
83. Biologically important
phospholipids
Biologically important
phospholipids
A) Glycerophospholipid:
Phosphatidic acid
Phosphatidyl glycerol
Diphosphatidyl glycerol
(cardiolipin)
Phosphatidyl choline (lecithin)
Phosphatidyl ethanolamine
(cephalin)
Phosphatidylinositol (lipositol)
Phosphatidylserine
Lyso phospholipid
85. Functions of phospholipidFunctions of phospholipid
Constitutes cell membrane
Membrane PL provides arachidonic
acid to synthesize eicosanoids
In bile, solubilize cholesterol & prevent
gall stone formation
Helps in coagulation (cephalin)
2nd
messenger for hormones
86. ContdContd
Surfactant in the lung to prevent
collapsing tendency of alveoli
(dipalmitoyl lecithin)
Lipotropic factor to prevent fatty liver
(lecithin)
Acts as PAF (plamalogen)
LP formation
89. DefinitionDefinition
Defined as a biochemical assembly
that contains
proteins
and
lipids bound to the proteins
which allow fats to move through the
water inside and outside the cells
90. Objective of lipoprotein
formation
Objective of lipoprotein
formation
To solubilize lipids in plasma
to facilitate their transport in
biological system
&
to provide efficient mechanism
for lipid delivery to the tissues
and lipid removal from the tissues
91.
92. Structure of lipoproteinStructure of lipoprotein
A nonpolar lipid core
(triacylglycerols and cholesteryl
esters)
A single surface layer of
amphipathic lipids (phospholipids
and cholesterol) & protein
(apolipoprotein or apoprotein)
Amphipathic lipids are oriented
so that their polar groups face
outward to the aqueous medium
93.
94. Function of lipoproteinFunction of lipoprotein
Chylomicron: Transports dietary
TG & CE from intestine to
peripheral tissues and liver
VLDL: Transports endogenous TG
from liver to extra hepatic
tissues
LDL: Transports cholesterol from
liver to extra hepatic tissues
HDL: Transports cholesterol from
extra hepatic tissues back to the
liver in an esterified form
100. Eicosanoids as local
hormone
Eicosanoids as local
hormone
They have specific effects on
target cells close to their site of
formation (autocrine/ paracrine
mediator)
They are rapidly degraded, so
they are not transported to distal
sites within the body
101. Functions of EicosanoidsFunctions of Eicosanoids
Can be described in terms of functions
of individual component like:
Prostanoids: Prostaglandins &
thromboxane
Leukotrienes
Lipoxins
103. ContdContd
1. Excess of prostaglandins are
related with inflammatory responses
like pain, fever, oedema etc
2. Prostacyclin (PG-I2): Are produced
mostly in vascular endothelium
causes:
Vasodilatation
Inhibition of platelet aggregation
104. ContdContd
3. Thromboxane A2 (TX-A2): Are
produced mostly in platelets causes:
Vasoconstriction
Platelet aggregation
Smooth muscle contraction
105. ContdContd
4. PG-E2 & PG-F2 :
Effects
on
PG-E2 PG-F2
Blood
vessel
Dilatation Constrictio
n
BP Lowering
of BP
-
Smooth
muscle
Relaxation Contractio
n
110. Clinical use of
Prostaglandin
Clinical use of
Prostaglandin
Control of inflammation by
suppression of PG synthesis
To induce childbirth
or abortion (PG-F2)
To prevent and treat peptic
ulcers by decreasing HCl
secretion (PG-E2)
Control of hypertension (PG-E2 &
PG-I2)
To prevent Thrombotic events
111. PG vs. True HormonesPG vs. True Hormones
Points PG True
hormones
Origin Almost all
tissues
Specialize
d glands
Site of
action
Locally Distant
sites
Transport
via blood
Not
transported
Transport
ed