Lipids along with its classification, EFA, A brief on phospholipids, cholesterol, lipoprotein and eicosanoids

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

9. CLASSIFICATION OF
LIPIDS
CLASSIFICATION OF
LIPIDS
1. Simple lipids
2. Complex lipids
3. Precursor and derived lipids

10. 1. SIMPLE LIPIDS1. SIMPLE LIPIDS
Esters of fatty acids with various
alcohols
Do not contain any non-lipid
substances
Includes fats and waxes

11. FatsFats
Esters of fatty acids with
glycerol
Fats in liquid state are called oil

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:

15. CONTDCONTD
B) Glycolipids
(glycosphingolipids):
 Lipids containing a fatty acid,
alcohol sphingosine &
carbohydrate

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

22. CONTDCONTD
Amphipathic
lipids
Polar group
Fatty acid -COOH group
Phospholipid PO4, Nitrogen base
Glycolipid Carbohydrate
moiety

23. CONTDCONTD
Amphipathic
lipids
Polar group
Bile salt -OH group,
glycine, taurine
Cholesterol -OH group

24. Dietary LipidDietary Lipid
Neutral fat/ Triacylglycerols
Cholesterol
Phospholipids

25. Lipids present in neural
tissues
Lipids present in neural
tissues
1. Phospholipids:
 Lecithin
 Cephalin
 Sphingomyelin/
Sphingophospholipid
 Plasmalogen
2. Glycolipids:
 Cerebroside
 Ganglioside
3. Sulfolipids:
 Sulfocerebroside

26. Neutral fat
(TG/TAG)

27. IntroductionIntroduction
 Synonym: Triglyceride (TG) /
Triacylglycerol (TAG)
 Triester of fatty acids with
glycerol

29. ContdContd
Neutral, because, they don’t have
any charge at normal body pH
Constituent FA : mostly palmitic,
stearic and oleic acids

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

35. ContdContd
Chemical properties:
 i) Hydrolysis: Produces fatty
acid & glycerol
 ii) Saponification: Hydrolysis by
alkali produces soap & glycerol

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

41. Fatty Acid

42. IntroductionIntroduction
Carboxyl group (-COOH)
containing organic acid
General formula: R-(CH2)n-COOH
Have an aliphatic hydrocarbon
chain with one –COOH group at
the end of the chain

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

48. CONTD
CH3-CH2……CH2 - CH2 - CH2- COOH
1234n
αβγω

49. Than
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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

55. ContdContd
Common source: Animal fat (butter,
ghee, dalda, milk fat, mutton fat, beef
fat etc), Vegetable oil (coconut/palm
oil), Vanashpati
Example: Palmitic acid, Stearic acid
etc

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

57. ContdContd
a) MUFA:
 Has 1 double bond
 e.g. Oleic acid (18C)
 Found in olive oil etc

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)

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

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)

66. Essential
Fatty Acid
(EFA)

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)

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

74. Cholester
ol

75. IntroductionIntroduction
 Most important sterol in human
body
 Possesses a steroid nucleus
(cyclopentano perhydro
phenatherene ring nucleus)

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

80. Phospholip
id

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

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

84. ContdContd
B) Sphingophospholipid
(Sphingomyelin)
Here alcohol is sphingol /
sphingosine

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

87. Lipoprotei
n

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

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

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

96. Eicosanoi
ds

97. IntroductionIntroduction
 Signaling molecules made by
oxidation of 20-carbon PUFA
(Arachidonic acid)
Or
 Prostaglandins and related
compounds are collectively
known as eicosanoids

98. ContdContd
It includes:
i. Prostaglandins (PG)
ii. Prostacyclin (PG-I2)
iii.Thromboxane (TX)
iv. Leukotrienes (LT)
v. Lipoxins (LX)
Prostanoids

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

102. 1. Prostanoids1. Prostanoids
Arachidonic acid
COX
PG-I2
TX-A2
PG-E2
PG-F2
PG-D2

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

106. ContdContd
Effects
on
PG-E2 PG-F2
Other
tissues
Renal
vasodilatatio
n, raised
GFR,
natriuresis
Uterine
contracti
on
Gastric
HCl
secretion
Inhibition -

107. 2. Leukotrienes2. Leukotrienes
Vasoconstriction
Smooth muscle contraction
Increased vascular permeability &
chemotaxis
Regulation of events of inflammation,
hypersensitivity & anaphylaxis

108. 3. Lipoxins3. Lipoxins
Vasodilatation
Inhibition of neutrophil chemotaxis

109. Prostaglandin antagonistsProstaglandin antagonists
 NSAIDs : Inhibit cyclooxygenase
 Corticosteroids:
Inhibit phospholipase
A2 production

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

112. ContdContd
Points PG True
hormones
Action on
parent
cells
Yes No
Synthesis
& storage
As per need
& not
stored in
tissues
Not such

113. Than
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