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Chemistry of lipid
Dr Ifat Ara Begum
Associate Professor
Department of Biochemistry
Dhaka Medical College, Dhaka
What is lipid?:
Lipids are heterogeneous group of
organic compounds, having a
common property of being
relatively insoluble in water &
soluble in non-polar organic
solvents like ether, chloroform,
benzene, alcohol .
 Lipids are not polymeric substances like proteins, polysaccharides &
nucleic acids
 Building block of most of the lipids: Fatty acid
 Lipids lack fatty acid: Cholesterol
Why you should know about chemistry of lipids?
 Essential roles of lipids in nutrition and health
 Understanding of many important biomedical
conditions, including obesity, DM &
atherosclerosis.
Biological importance / functions of Lipid
Includes biological importance / functions of:
 Neutral fat / Triglyceride (TG) / Triacylglycerol (TAG)
 Phospholipid
 Glycolipid
 Cholesterol
 Energy:
Source of energy
 Important storage form of energy
(as fat)
 Constitute biological membrane
 Provides :
Essential fatty acids
 Arachidonic acid for synthesis of
eicosanoids
 2nd messenger for hormones
 Helps in:
Absorption of fat soluble vitamins
 Coagulation
 Acts as:
 Subcutaneous thermal insulator
 Perineural electrical insulator
 Mechanical cushion around internal organs to protect them
from mechanical injury
 Precursor of steroid hormone, bile acid and vitamin D
 Lipotropic factor
 Surfactant to prevent collapsing tendency of alveoli
Classification of
Lipid
Classification based on composition
Simple Lipids Complex / Compound Lipids Derived Lipids
Esters of fatty acids
with alcohol
Esters of fatty acids with alcohol
along with other non lipid
substances
Derivatives obtained by hydrolysis of simple &
complex lipids which still possess the general
characteristics of lipids
Simple lipid = Fatty
acid + Alcohol
(Do not contain any
non-lipid substances)
Complex lipid = Fatty acid +
Alcohol + Other non lipid
substances
Hydrocarbon ring + Hydrocarbon side chain
Examples:
Neutral fat, Wax
Examples:
Phospholipid, Glycolipid &
Lipoprotein
Examples:
Fatty acid, Glycerol , Alcohol, Steroids,
Cholesterol, Prostaglandins, Ketone bodies,
Fat soluble vitamins etc
Classification based on polarity
Non polar lipid Polar Lipid / Amphipathic Lipid
Hydrophobic Lipids having both polar (hydrophilic) & non polar
(hydrophobic) groups
Water insoluble Show limited degree of water solubility due to their
hydrophilic groups
Example:
TAG
 Different esters (cholesterol ester,
retinol ester, vitamin D ester) etc
Example:
Fatty acid (-COOH group is polar group)
Cholesterol (-OH group)
Phospholipid (PO4 , Nitrogen base) etc
Structural versus depot lipid
Structural lipid / Tissue Lipid Depot Lipid
Constitute biological membrane Constitute storage lipid in adipose tissue
Chemically, they are Glycolipid, Phospholipid
& Cholesterol
Chemically, they are TAG
Contain mostly UFA Contain mostly SFA
Turnover rate is slow Turnover rate is rapid
Half life is long Half life is short (˂ 2 days)
Precursor of cellular signaling molecules Source of energy
Dietary lipids:
TAG : 90%
 Cholesterol
 Phospholipid
Neutral lipids:
 They carry no charge at normal body pH
 Examples:
 TAG
 Cholesterol & cholesterol esters
Monoglyceride, diglyceride
Lipids present in neural tissues:
 Phospholipids:
Lecithin, Cephalin, Sphingomyelin / Sphingophospholipid
 Glycolipids:
Cerebroside, Ganglioside, Sulfocerebroside
A short detail on some
important types of
lipids
1. Neutral fat
(TG / TAG)
G
L
Y
C
E
R
O
L
Fatty Acid 1
Fatty Acid 2
Fatty Acid 3
 Triester of fatty acids with glycerol
 Regarded as Neutral, because, they don’t have any charge at normal body pH
 If 3 fatty acids are of same type: Simple TAG
 If 3 fatty acids are of different types: Mixed TAG & it predominates in nature
 Source of neutral fat:
Plant source : Contains more UFA.
e.g. vegetable oil
 Animal source: Contains more
SFA. e.g. ghee, egg etc
 Fatty acids found mostly in neutral fat:
Palmitic acid, Stearic acid, Oleic acid
Fat Oil
Triester of FA with
glycerol that remains
Solid at room
temperature (25 degree
C)
Triester of FA with
glycerol that remains
liquid at room temperature
(In other words, fat in
liquid state)
Contains more
saturated fatty acid
Contains more unsaturated
fatty acid
This difference is purely physical. Chemically both
are same (triacyl glycerol)
Physical properties of fat:
 Colorless, tasteless, odorless
 Neutral
 Water insoluble but soluble in fat solvents
 Specific gravity: ˂ 1.0
 Makes emulsion with water
Chemical properties of fat:
Hydrolysis: On hydrolysis, fat produces FA
and glycerol
Saponification: Hydrolysis of fat by alkali to
produce glycerol & soap
Rancidity: Auto oxidation of fat by
atmospheric oxygen to peroxides, epoxides &
aldehydes leading to unpleasant taste & odor
with change of color
Peroxidation: Auto oxidation in vivo to
produce lipid peroxides and free radicals
which causes tissue damage & initiate the
process of malignancy, aging &
atherosclerosis
Hydrogenation & hardening: UFA of fat by
absorbing hydrogen turns into SFA which
elevates melting point of fat & makes it solid
at room temperature
Biological importance / functions of Fat / TAG
 Source of energy
 Storage form of energy
 Add taste & palatability to food
 Provides EFA
 Helps in absorption of fat soluble
vitamins
 Acts as:
 Subcutaneous thermal insulator
 Perineural electrical insulator
 Mechanical cushion around internal organs
to protect them from mechanical injury
 Cosmetic effect:
Gives shape & contour to body
 High plasma TAG level increases the risk of:
 Coronary artery disease
 Fatty liver disease
 Acute pancreatitis
2. WAX
 Esters of fatty acids with long chain monohydric alcohol
 Examples:
Cholesterol ester (Cholesterol + FA)
 Vitamin D ester (Vitamin D + FA)
 Retinol ester (Retinol +FA)
3. Phospholipid
 Esters of fatty acid with alcohol attached to
phosphoric acid, with / without nitrogen base
[i.e. Phospholipid = Fatty acid + Alcohol +
Phosphoric acid ± Nitrogen base]
 Complex / Compound lipid
 In most of the cases, nitrogen base is present
 H3PO4 is essential component
 Has amphipathic nature
 Based on nature of alcohol present, two types of
PL – Glycerophospholipid &
Sphingophospholipid (Sphingomyelin)
A) Glycerophospholipid:
Here the alcohol is glycerol
FA + Glycerol + Phosphoric acid ±
Nitrogen base
 Fatty acids are attached with 1st &
2nd carbons and phosphate is
attached with 3rd carbon of glycerol
 At least one UFA is present usually
at 2nd carbon of glycerol
Primary glycerophospholipid: Phosphatidic
acid
 Others are derivatives of phosphatidic acid
 Major FA found in glycerophospholipid:
- PUFA (EFA)
- MUFA (Oleic acid, palmitoleic acid)
- SFA (Palmitic acid, stearic acid)
Common Glycerophospholipid Composition Nitrogen base
Phosphatidic acid (PA) FA + Glycerol + H3PO4 Absent
Lecithin (Phosphatidylcholine) PA + Choline Choline
Cephalin (Phosphatidylethanol amine) PA + Ethanol amine Ethanol amine
Phosphatidylserine PA + Serine Serine
Phosphatidylinositol (Lipositol) PA + Inositol Absent
Phosphatidylglycerol PA + Glycerol Absent
Diphosphatidylglycerol (Cardiolipin) 2 (PA + Glycerol) Absent
Lyso phospholipids Glycerophospholipid with one FA
removed from C2 or C1 of
glycerol
Mostly present
B) Sphingophospholipid /
Sphingomyelin:
 Constitute biological membrane & myelin sheath
 Here the alcohol is sphingol (sphingosine)
 FA + Sphingol + Phosphoric acid + Choline
 As (FA + Sphingol) together make Ceramide, so
we can write
Sphingomyelin = Ceramide + H3PO4 + Choline
 FA : 16-26 C SFA (palmitic acid, stearic acid)
 Choline: Nitrogenous substance
 H3PO4 & Choline : Non lipid substances
Biological importance / functions of Phospholipid (esp. glyceroPL)
 Constitutes biological membrane.
 Membrane PL provides arachidonic acid to synthesize
eicosanoids
 Helps in:
 Coagulation : Cephalin
 Lipoprotein formation
 Acts as:
 Source of 2nd messenger for hormones: Phosphatidyl inositol
 Lipotropic factor to prevent fatty liver: Lecithin
 Surfactant in the lung to prevent collapsing tendency of
alveoli : Dipalmitoyl lecithin
 In bile, they
solubilize cholesterol
&
prevent gall stone
formation
4. Glycolipid /
Glycosphingolipid
 Lipids containing carbohydrate
 FA + Sphingol (Sphingosine) + Carbohydrate
[As (FA + Sphingol) together make Ceramide, so
we can write
Glycolipid = Ceramide + Carbohydrate]
 Lipid part : FA with sphingol
 Non lipid part: Carbohydrate
 Carbohydrates present here: Monosaccharide,
amino sugar, sialic acid
 FA present here: Mostly cerebronic acid, nervonic
acid, lignoceric acid etc
Types of Glycolipids based on nature of carbohydrate
component
Cerebrosides Gangliosides
Carbohydrate component:
Monosaccharide
Example:
Glucocerebroside,
Galactocerebroside
Carbohydrate component:
Monosaccharide
+
Complex carbohydrate (like
amino sugar, sialic acid)
Sulfolipid :
 Synonym: Sulfatide / Sulfoglycolipid
 Glycolipid with SO4 group
 Example:
Sulfocerebrosides like glucocerebroside SO4 , galactocerebroside SO4
Biological importance / functions of Glycolipids
 Constitutes cell membrane.
 Regulates:
Cellular interaction
Inter cellular communication
Cellular growth and development
 Acts as:
 Cell surface receptor
 Blood group substance
 Tumour antigen
5. Lipoproteins
Lipid
Protein
Lipoprotein
 Lipoproteins are globular
macromolecular complex consisting
of lipids and specific protein
(apoprotein / apolipoprotein)
 Purpose / Importance of LP
formation:
To solubilize lipids in plasma
water to facilitate their transport in
biological system
To provide efficient mechanism
for lipid delivery to the tissues &
lipid removal from the tissues
Organization of LP:
Constituents of LP (TAG, CE,
PL, FC, Apoprotein) are
organized in to a globular
structure with -
 a central core of non polar
hydrophobic lipid (TAG & CE)
 surrounded by a middle layer
of amphipathic lipids (PL &
FC)
 with an external interrupted
layer of apoproteins
Types
of
Lipoprotein
Chylomicron
Very low density lipoproteins - VLDL
Low density lipoprotein – LDL
High density lipoprotein - HDL
Others: CMR, VLDLR (IDL)
• C-I,II, III:
Liver
• Liver
• Macrophage
• B-48: Intestine
• B-100: Liver
• A-I: Liver & Intestine
• A-II:Liver
• A-IV: Intestine
Apo
A
Apo
B
Apo
C
Apo
E
Protein component of LP that provides
hydrophilic character to LP particles
to facilitate their transport in aqueous
plasma
Act as :
- Cofactor (activator) for enzymes of
LP metabolism (e.g. Apo C-II for LPL)
- Inhibitor of enzymes of LP
metabolism (e.g. Apo A-II for LPL)
Acts As Ligand to recognize LP receptors
on cell surface for uptake of
LP.
e.g. Apo A is ligand for HDL receptor
- Maintains structural stability of LP
- Determines metabolic fates of LP and
facilitate exchange of lipids between LPs
Functions / Importance of
Apoproteins in LP
Types of
LP
(origin)
Size Density Apoprotein
(%)
Lipid
(%)
Main lipid apoprotein
Inherent Acquired
CM
(intestine)
2 98 Dietary TAG (90% of
lipid core)
B48 & A C & E
(from HDL)
VLDL
(liver)
8 92 Endogenous TAG
(80% of lipid core)
B100 C & E
(from HDL)
LDL
(from
VLDL in
blood)
20 80 Cholesterol (65% of
lipid core),
PL
B100 -
HDL
(Liver)
50 50 Cholesterol
PL
A, C, E -
Chylomicron:
- Supports exogenous (dietary) lipid
transport (esp. TAG & Cholesterol)
- Carries dietary lipids from intestine to
liver & other peripheral tissues
VLDL:
- Supports endogenous lipids transport
- Carries cholesterol (via LDL) & TAG from
liver to peripheral tissues
- Precursor of LDL
LDL:
- Supports endogenous lipid transport
- Receives cholesterol from VLDL &
HDL and then deposit cholesterol to
peripheral tissues
HDL:
- Supports endogenous lipid transport
- Acts as a reservoir of apoprotein
- Helps in CM & VLDL metabolism
- Through RCT, acts as cholesterol scavengers in
peripheral tissues and removes cholesterol from
peripheral tissues back to liver
Functions of diff. LP
Remember
 93% of total body cholesterol resides in intracellular
compartment
 Only 7% is found in plasma where cholesterol is carried by :
LDL (60-70%)
HDL (20-30%)
 VLDL (10-15%)
 Atherogenic LPs : VLDL, CMR, IDL, LDL
 Antiatherogenic LP: HDL
6. Fatty Acid
 Carboxyl group containing organic acid
 Weak acid
 There is an aliphatic hydrocarbon chain with one carboxyl group at the end
of the chain
 Amphipathic character (hydrophilic carboxylate anion COO- & hydrophobic
hydrocarbon chain)
 General formula: CH3 - (CH2)n – COOH
 Short chain FA is water soluble because of their short
hydrophobic hydrocarbon chain
 Long chain FA is highly water insoluble because of their long /
predominant hydrophobic hydrocarbon portion, so they are
transported in circulation with plasma albumin
Two forms in body:
i. As esters in neutral fat & oils
ii. In unesterified form as FFA (a transport form in plasma)
 Distribution of plasma FA:
 45% found with TAG
 35% with PL
 15% with CE
 5% as FFA
 >90% of FA in human body contains even no. of carbon atoms (mostly14 to
24 C)
Of these most abundant are 16C FA (Palmitic acid) or 18C FA (Stearic acid)
 <5% of FA in human body contains odd no. of carbon atoms
Sources of FA:
i. Endogenous sources: Synthesis of NEFA within the body
ii. Exogenous / Dietary sources:
• For saturated FA: Animal fat, milk, butter, ghee, coconut oil, palm
oil, Vanashpati (hydrogenated fat) etc
• For Unsaturated FA: vegetable oil, fish oil, cod liver oil etc
Numbering & designation of carbons in Fatty acid
CH3-CH2…… CH2 - CH2 - CH2- COOH
1234
αβγω
Classification of fatty acid
Three types of classification:
A. Based on total number of carbon (chain length)
B. Based on saturation of carbon
C. Nutritional classification
Based on chain length :
i) Short chain Fatty acid:
 No. of C: <10
Mostly found in milk
e.g. Acetic acid (2C), Propionic acid
(3C) etc
ii) Long chain Fatty acid:
 No. of C: >10
e.g. Palmitic acid (16C),
Stearic acid (18C) etc
Fatty Acid
(Based on saturation of
carbon)
Unsaturated
MUFA
(Oleic acid)
PUFA
(EFA)
Saturated
Fatty Acid
(Nutritional Classification)
NEFA
Palmitic acid, Stearic
acid
EFA
Linoleic acid, Linolenic
acid
Delta numbering system for UFA:
 C atoms are numbered from –COOH
group
 Total C number, total no. of double
bond & the position of the double
bond are indicated numerically
 Linoleic acid: 18 : 2 ; 9 ,12
[ 18C fatty acid with 2 double bonds,
which are placed between carbon 9 – 10
and carbon 12 – 13]
Omega (ω) numbering system for
UFA:
 C atoms are numbered starting from ω
carbon end (methyl end) of chain
 Position / distance of first double bond from
ω carbon is mentioned
 ω3- fatty acid / Linolenic acid:
[The first double bond closest to ω-carbon
end begins at 3rd carbon counted from this end]
Cis Isomeric Form of FA Trans Isomeric Form of FA
Double bonds (C = C) of UFA are
arranged in cis isomeric form where
both hydrogen atoms are present on the
same side of double bonds
Double bonds (C = C) of UFA are arranged in trans
isomeric form where both hydrogen atoms are present on
the opposite side of double bonds
It makes UFA more fluid It makes UFA less fluid and trans FA behave like SFA
These are found in nature These are not commonly found in nature. They are
produced as a byproduct during hydrogenation treatment
on PUFA of natural oil to make it harden fat. e.g. solid
margarine (hydrogenated vegetable oil)
Trans FA containing TAG is called Trans fat
Importance of Trans FA / Fat:
Consumption of trans FA / trans fat elevates LDL and lowers HDL, so, more risk of
coronary artery disease & DM
Properties of fatty acids
Physical properties:
 Water solubility:
 Melting point
 Isomerism
Chemical properties:
Soap formation
Ester formation
 Oxidation
Hydrogenation
Halogenation
Biological importance / functions of fatty acids
 Metabolic fuel : When oxidized , they form ATP
 Participates in synthesis of
 PL
 GL
 Cholesterol ester
 FA derivatives act as intracellular messenger. e.g. PG
 Risk of atherosclerosis & CAD:
 SFA & trans FA increase LDL & decrease HDL, so the risk of CAD increases.
 UFA decreases LDL, so the risk of CAD decreases
1. Linoleic acid : 18 C ω6 fatty
acid with 2 double bonds 2. Linolenic acid : 18 C ω3 fatty acid
with 3 double bonds
Arachidonic acid : 20 C ω6
fatty acid with 4 double bonds
[Semi essential as can be
synthesized from Linoleic acid]
Functions:
- Component of biological membrane & maintain
its fluidity
- Precursor of Eicosanoids
- Helps in Gonadal function, reproduction, Vision,
Growth
- Reduce plasma cholesterol by increasing its
excretion via bile & its oxidation to bile acid
Essential Fatty Acids
(PUFA)
Deficiency of EFA:
 Retarded growth
 Impaired gonadal function & reproductive
failure
 Dermatitis
 Degenerative changes in arterial wall
 Fatty liver
 Poor wound healing & hair loss
 Faulty vision
Sources of EFA:
 Vegetable oil (Except coconut oil
and palm oil)
 Fish oil (Linolenic acid rich)
 Cod liver oil (Linoleic acid rich)
7. Cholesterol
 A 27 C Amphipathic lipid containing steroid
nucleus
 Steroid nucleus :
 Cyclopentano perhydro phenatherene nucleus
 A 19 C compound made of 4 fused non
aromatic hydrocarbon rings (A, B, C, D)
 Two methyl groups denoted as C18 and C19
 Steroid nucleus is attached with
- One OH group at C3
- A branched chain of 8 carbons at C17
 A double bond between C5 and C6
Functions of cholesterol:
 Constituent of biological membrane
 Precursor of:
Steroid hormones
 Bile acid , bile salts
 Vitamin D
 High plasma level of cholesterol is associated
with atherosclerotic disorders like
- Stroke
- Coronary artery disease etc
Sources of Cholesterol:
 Endogenous synthesis
 Exogenous / Dietary: Only
from animal foods . e.g. egg
yolk, liver, mutton, prawn, beef
etc
“All sterols are steroids but all steroids are not sterols”
Steroid substances:
Steroid nucleus + one oxygen atom
at C-3 position of nucleus.
e.g. Cortisol, Aldosterone,
Testosterone etc
Sterol compounds:
Steroid nucleus + one hydroxyl
group at C-3 position of nucleus.
e.g. Cholesterol, Bile acid, Vitamin
D etc
8. Eicosanoids
 Signaling molecules derived from made by oxidation of 20 C PUFA
(eicosanoic acid )
Or
Prostaglandins and related compounds
Name of the eicosanoids
Eicosanoid includes:
 Prostaglandins (PG)
 Prostacyclin (PG-I2)
 Thromboxane (TX)
 Leukotrienes (LT)
 Lipoxins (LX)
Prostanoid
Justify, “Prostaglandins are local hormones”
 They act on target cells close to their site of formation to
produce specific effects
 They are rapidly degraded,
so they are not transported to distal sites within the body
Justify, “Prostaglandins are not true hormones”
Points PG True hormones
Origin Almost all tissues Specialized glands
Site of action Locally Distant sites
Transport via blood Not transported Transported
Action on parent cells Yes No
Synthesis & storage Synthesis as per need & not stored
in tissues
Not such
Clinical use of Prostaglandins
 Control of :
 Inflammation by suppression of PG
synthesis
 Hypertension (PG E2 & PG I2)
 Relief of asthma and nasal congestion:
PG E2
 To prevent :
 Peptic ulcers by decreasing HCl
secretion (PG E2) and treatment as
well
 Thrombotic events (PG I2)
 Control of hypertension:
PG E2 & PG I2
9. Ketone Body
 Water-soluble derived lipid
 Metabolic products that are produced in excess during excessive
breakdown of fatty acid
 Freely transportable form of acetyl units (don’t need to be with LP
/albumin for transportation in blood)
 Acetoacetate, Beta hydroxy butyrate, and acetone are often referred to
as ”Ketone bodies”
 “Acetoacetate” is the primary ketone body.
Interrelationship of
ketone bodies
Ketone
bodies are
synthesized
only in liver
Alternate sources to
glucose for energy
Production of ketone bodies under
conditions of cellular energy deprivation
Utilization of ketone
bodies by the brain
Chemistry of lipid , september 2020

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Chemistry of lipid , september 2020

  • 1. Chemistry of lipid Dr Ifat Ara Begum Associate Professor Department of Biochemistry Dhaka Medical College, Dhaka
  • 2. What is lipid?: Lipids are heterogeneous group of organic compounds, having a common property of being relatively insoluble in water & soluble in non-polar organic solvents like ether, chloroform, benzene, alcohol .
  • 3.  Lipids are not polymeric substances like proteins, polysaccharides & nucleic acids  Building block of most of the lipids: Fatty acid  Lipids lack fatty acid: Cholesterol
  • 4. Why you should know about chemistry of lipids?  Essential roles of lipids in nutrition and health  Understanding of many important biomedical conditions, including obesity, DM & atherosclerosis.
  • 5. Biological importance / functions of Lipid Includes biological importance / functions of:  Neutral fat / Triglyceride (TG) / Triacylglycerol (TAG)  Phospholipid  Glycolipid  Cholesterol
  • 6.  Energy: Source of energy  Important storage form of energy (as fat)  Constitute biological membrane  Provides : Essential fatty acids  Arachidonic acid for synthesis of eicosanoids  2nd messenger for hormones  Helps in: Absorption of fat soluble vitamins  Coagulation
  • 7.  Acts as:  Subcutaneous thermal insulator  Perineural electrical insulator  Mechanical cushion around internal organs to protect them from mechanical injury  Precursor of steroid hormone, bile acid and vitamin D  Lipotropic factor  Surfactant to prevent collapsing tendency of alveoli
  • 9. Classification based on composition Simple Lipids Complex / Compound Lipids Derived Lipids Esters of fatty acids with alcohol Esters of fatty acids with alcohol along with other non lipid substances Derivatives obtained by hydrolysis of simple & complex lipids which still possess the general characteristics of lipids Simple lipid = Fatty acid + Alcohol (Do not contain any non-lipid substances) Complex lipid = Fatty acid + Alcohol + Other non lipid substances Hydrocarbon ring + Hydrocarbon side chain Examples: Neutral fat, Wax Examples: Phospholipid, Glycolipid & Lipoprotein Examples: Fatty acid, Glycerol , Alcohol, Steroids, Cholesterol, Prostaglandins, Ketone bodies, Fat soluble vitamins etc
  • 10. Classification based on polarity Non polar lipid Polar Lipid / Amphipathic Lipid Hydrophobic Lipids having both polar (hydrophilic) & non polar (hydrophobic) groups Water insoluble Show limited degree of water solubility due to their hydrophilic groups Example: TAG  Different esters (cholesterol ester, retinol ester, vitamin D ester) etc Example: Fatty acid (-COOH group is polar group) Cholesterol (-OH group) Phospholipid (PO4 , Nitrogen base) etc
  • 11.
  • 12. Structural versus depot lipid Structural lipid / Tissue Lipid Depot Lipid Constitute biological membrane Constitute storage lipid in adipose tissue Chemically, they are Glycolipid, Phospholipid & Cholesterol Chemically, they are TAG Contain mostly UFA Contain mostly SFA Turnover rate is slow Turnover rate is rapid Half life is long Half life is short (˂ 2 days) Precursor of cellular signaling molecules Source of energy
  • 13. Dietary lipids: TAG : 90%  Cholesterol  Phospholipid Neutral lipids:  They carry no charge at normal body pH  Examples:  TAG  Cholesterol & cholesterol esters Monoglyceride, diglyceride Lipids present in neural tissues:  Phospholipids: Lecithin, Cephalin, Sphingomyelin / Sphingophospholipid  Glycolipids: Cerebroside, Ganglioside, Sulfocerebroside
  • 14. A short detail on some important types of lipids
  • 16. G L Y C E R O L Fatty Acid 1 Fatty Acid 2 Fatty Acid 3
  • 17.  Triester of fatty acids with glycerol  Regarded as Neutral, because, they don’t have any charge at normal body pH  If 3 fatty acids are of same type: Simple TAG  If 3 fatty acids are of different types: Mixed TAG & it predominates in nature
  • 18.  Source of neutral fat: Plant source : Contains more UFA. e.g. vegetable oil  Animal source: Contains more SFA. e.g. ghee, egg etc  Fatty acids found mostly in neutral fat: Palmitic acid, Stearic acid, Oleic acid
  • 19. Fat Oil Triester of FA with glycerol that remains Solid at room temperature (25 degree C) Triester of FA with glycerol that remains liquid at room temperature (In other words, fat in liquid state) Contains more saturated fatty acid Contains more unsaturated fatty acid This difference is purely physical. Chemically both are same (triacyl glycerol)
  • 20. Physical properties of fat:  Colorless, tasteless, odorless  Neutral  Water insoluble but soluble in fat solvents  Specific gravity: ˂ 1.0  Makes emulsion with water
  • 21. Chemical properties of fat: Hydrolysis: On hydrolysis, fat produces FA and glycerol Saponification: Hydrolysis of fat by alkali to produce glycerol & soap Rancidity: Auto oxidation of fat by atmospheric oxygen to peroxides, epoxides & aldehydes leading to unpleasant taste & odor with change of color Peroxidation: Auto oxidation in vivo to produce lipid peroxides and free radicals which causes tissue damage & initiate the process of malignancy, aging & atherosclerosis Hydrogenation & hardening: UFA of fat by absorbing hydrogen turns into SFA which elevates melting point of fat & makes it solid at room temperature
  • 22. Biological importance / functions of Fat / TAG  Source of energy  Storage form of energy  Add taste & palatability to food  Provides EFA  Helps in absorption of fat soluble vitamins  Acts as:  Subcutaneous thermal insulator  Perineural electrical insulator  Mechanical cushion around internal organs to protect them from mechanical injury  Cosmetic effect: Gives shape & contour to body  High plasma TAG level increases the risk of:  Coronary artery disease  Fatty liver disease  Acute pancreatitis
  • 24.  Esters of fatty acids with long chain monohydric alcohol  Examples: Cholesterol ester (Cholesterol + FA)  Vitamin D ester (Vitamin D + FA)  Retinol ester (Retinol +FA)
  • 26.  Esters of fatty acid with alcohol attached to phosphoric acid, with / without nitrogen base [i.e. Phospholipid = Fatty acid + Alcohol + Phosphoric acid ± Nitrogen base]  Complex / Compound lipid  In most of the cases, nitrogen base is present  H3PO4 is essential component  Has amphipathic nature  Based on nature of alcohol present, two types of PL – Glycerophospholipid & Sphingophospholipid (Sphingomyelin)
  • 27. A) Glycerophospholipid: Here the alcohol is glycerol FA + Glycerol + Phosphoric acid ± Nitrogen base  Fatty acids are attached with 1st & 2nd carbons and phosphate is attached with 3rd carbon of glycerol  At least one UFA is present usually at 2nd carbon of glycerol
  • 28. Primary glycerophospholipid: Phosphatidic acid  Others are derivatives of phosphatidic acid  Major FA found in glycerophospholipid: - PUFA (EFA) - MUFA (Oleic acid, palmitoleic acid) - SFA (Palmitic acid, stearic acid)
  • 29. Common Glycerophospholipid Composition Nitrogen base Phosphatidic acid (PA) FA + Glycerol + H3PO4 Absent Lecithin (Phosphatidylcholine) PA + Choline Choline Cephalin (Phosphatidylethanol amine) PA + Ethanol amine Ethanol amine Phosphatidylserine PA + Serine Serine Phosphatidylinositol (Lipositol) PA + Inositol Absent Phosphatidylglycerol PA + Glycerol Absent Diphosphatidylglycerol (Cardiolipin) 2 (PA + Glycerol) Absent Lyso phospholipids Glycerophospholipid with one FA removed from C2 or C1 of glycerol Mostly present
  • 30. B) Sphingophospholipid / Sphingomyelin:  Constitute biological membrane & myelin sheath  Here the alcohol is sphingol (sphingosine)  FA + Sphingol + Phosphoric acid + Choline  As (FA + Sphingol) together make Ceramide, so we can write Sphingomyelin = Ceramide + H3PO4 + Choline  FA : 16-26 C SFA (palmitic acid, stearic acid)  Choline: Nitrogenous substance  H3PO4 & Choline : Non lipid substances
  • 31. Biological importance / functions of Phospholipid (esp. glyceroPL)  Constitutes biological membrane.  Membrane PL provides arachidonic acid to synthesize eicosanoids  Helps in:  Coagulation : Cephalin  Lipoprotein formation  Acts as:  Source of 2nd messenger for hormones: Phosphatidyl inositol  Lipotropic factor to prevent fatty liver: Lecithin  Surfactant in the lung to prevent collapsing tendency of alveoli : Dipalmitoyl lecithin  In bile, they solubilize cholesterol & prevent gall stone formation
  • 33.  Lipids containing carbohydrate  FA + Sphingol (Sphingosine) + Carbohydrate [As (FA + Sphingol) together make Ceramide, so we can write Glycolipid = Ceramide + Carbohydrate]  Lipid part : FA with sphingol  Non lipid part: Carbohydrate  Carbohydrates present here: Monosaccharide, amino sugar, sialic acid  FA present here: Mostly cerebronic acid, nervonic acid, lignoceric acid etc
  • 34. Types of Glycolipids based on nature of carbohydrate component Cerebrosides Gangliosides Carbohydrate component: Monosaccharide Example: Glucocerebroside, Galactocerebroside Carbohydrate component: Monosaccharide + Complex carbohydrate (like amino sugar, sialic acid)
  • 35.
  • 36.
  • 37. Sulfolipid :  Synonym: Sulfatide / Sulfoglycolipid  Glycolipid with SO4 group  Example: Sulfocerebrosides like glucocerebroside SO4 , galactocerebroside SO4
  • 38. Biological importance / functions of Glycolipids  Constitutes cell membrane.  Regulates: Cellular interaction Inter cellular communication Cellular growth and development  Acts as:  Cell surface receptor  Blood group substance  Tumour antigen
  • 40. Lipid Protein Lipoprotein  Lipoproteins are globular macromolecular complex consisting of lipids and specific protein (apoprotein / apolipoprotein)  Purpose / Importance of LP formation: To solubilize lipids in plasma water to facilitate their transport in biological system To provide efficient mechanism for lipid delivery to the tissues & lipid removal from the tissues
  • 41. Organization of LP: Constituents of LP (TAG, CE, PL, FC, Apoprotein) are organized in to a globular structure with -  a central core of non polar hydrophobic lipid (TAG & CE)  surrounded by a middle layer of amphipathic lipids (PL & FC)  with an external interrupted layer of apoproteins
  • 42. Types of Lipoprotein Chylomicron Very low density lipoproteins - VLDL Low density lipoprotein – LDL High density lipoprotein - HDL Others: CMR, VLDLR (IDL)
  • 43. • C-I,II, III: Liver • Liver • Macrophage • B-48: Intestine • B-100: Liver • A-I: Liver & Intestine • A-II:Liver • A-IV: Intestine Apo A Apo B Apo C Apo E
  • 44. Protein component of LP that provides hydrophilic character to LP particles to facilitate their transport in aqueous plasma Act as : - Cofactor (activator) for enzymes of LP metabolism (e.g. Apo C-II for LPL) - Inhibitor of enzymes of LP metabolism (e.g. Apo A-II for LPL) Acts As Ligand to recognize LP receptors on cell surface for uptake of LP. e.g. Apo A is ligand for HDL receptor - Maintains structural stability of LP - Determines metabolic fates of LP and facilitate exchange of lipids between LPs Functions / Importance of Apoproteins in LP
  • 45. Types of LP (origin) Size Density Apoprotein (%) Lipid (%) Main lipid apoprotein Inherent Acquired CM (intestine) 2 98 Dietary TAG (90% of lipid core) B48 & A C & E (from HDL) VLDL (liver) 8 92 Endogenous TAG (80% of lipid core) B100 C & E (from HDL) LDL (from VLDL in blood) 20 80 Cholesterol (65% of lipid core), PL B100 - HDL (Liver) 50 50 Cholesterol PL A, C, E -
  • 46. Chylomicron: - Supports exogenous (dietary) lipid transport (esp. TAG & Cholesterol) - Carries dietary lipids from intestine to liver & other peripheral tissues VLDL: - Supports endogenous lipids transport - Carries cholesterol (via LDL) & TAG from liver to peripheral tissues - Precursor of LDL LDL: - Supports endogenous lipid transport - Receives cholesterol from VLDL & HDL and then deposit cholesterol to peripheral tissues HDL: - Supports endogenous lipid transport - Acts as a reservoir of apoprotein - Helps in CM & VLDL metabolism - Through RCT, acts as cholesterol scavengers in peripheral tissues and removes cholesterol from peripheral tissues back to liver Functions of diff. LP
  • 47. Remember  93% of total body cholesterol resides in intracellular compartment  Only 7% is found in plasma where cholesterol is carried by : LDL (60-70%) HDL (20-30%)  VLDL (10-15%)  Atherogenic LPs : VLDL, CMR, IDL, LDL  Antiatherogenic LP: HDL
  • 49.  Carboxyl group containing organic acid  Weak acid  There is an aliphatic hydrocarbon chain with one carboxyl group at the end of the chain  Amphipathic character (hydrophilic carboxylate anion COO- & hydrophobic hydrocarbon chain)  General formula: CH3 - (CH2)n – COOH
  • 50.  Short chain FA is water soluble because of their short hydrophobic hydrocarbon chain  Long chain FA is highly water insoluble because of their long / predominant hydrophobic hydrocarbon portion, so they are transported in circulation with plasma albumin Two forms in body: i. As esters in neutral fat & oils ii. In unesterified form as FFA (a transport form in plasma)
  • 51.  Distribution of plasma FA:  45% found with TAG  35% with PL  15% with CE  5% as FFA  >90% of FA in human body contains even no. of carbon atoms (mostly14 to 24 C) Of these most abundant are 16C FA (Palmitic acid) or 18C FA (Stearic acid)  <5% of FA in human body contains odd no. of carbon atoms
  • 52. Sources of FA: i. Endogenous sources: Synthesis of NEFA within the body ii. Exogenous / Dietary sources: • For saturated FA: Animal fat, milk, butter, ghee, coconut oil, palm oil, Vanashpati (hydrogenated fat) etc • For Unsaturated FA: vegetable oil, fish oil, cod liver oil etc
  • 53. Numbering & designation of carbons in Fatty acid CH3-CH2…… CH2 - CH2 - CH2- COOH 1234 αβγω
  • 54. Classification of fatty acid Three types of classification: A. Based on total number of carbon (chain length) B. Based on saturation of carbon C. Nutritional classification
  • 55. Based on chain length : i) Short chain Fatty acid:  No. of C: <10 Mostly found in milk e.g. Acetic acid (2C), Propionic acid (3C) etc ii) Long chain Fatty acid:  No. of C: >10 e.g. Palmitic acid (16C), Stearic acid (18C) etc Fatty Acid (Based on saturation of carbon) Unsaturated MUFA (Oleic acid) PUFA (EFA) Saturated
  • 56.
  • 57. Fatty Acid (Nutritional Classification) NEFA Palmitic acid, Stearic acid EFA Linoleic acid, Linolenic acid
  • 58. Delta numbering system for UFA:  C atoms are numbered from –COOH group  Total C number, total no. of double bond & the position of the double bond are indicated numerically  Linoleic acid: 18 : 2 ; 9 ,12 [ 18C fatty acid with 2 double bonds, which are placed between carbon 9 – 10 and carbon 12 – 13] Omega (ω) numbering system for UFA:  C atoms are numbered starting from ω carbon end (methyl end) of chain  Position / distance of first double bond from ω carbon is mentioned  ω3- fatty acid / Linolenic acid: [The first double bond closest to ω-carbon end begins at 3rd carbon counted from this end]
  • 59.
  • 60. Cis Isomeric Form of FA Trans Isomeric Form of FA Double bonds (C = C) of UFA are arranged in cis isomeric form where both hydrogen atoms are present on the same side of double bonds Double bonds (C = C) of UFA are arranged in trans isomeric form where both hydrogen atoms are present on the opposite side of double bonds It makes UFA more fluid It makes UFA less fluid and trans FA behave like SFA These are found in nature These are not commonly found in nature. They are produced as a byproduct during hydrogenation treatment on PUFA of natural oil to make it harden fat. e.g. solid margarine (hydrogenated vegetable oil) Trans FA containing TAG is called Trans fat
  • 61. Importance of Trans FA / Fat: Consumption of trans FA / trans fat elevates LDL and lowers HDL, so, more risk of coronary artery disease & DM
  • 62. Properties of fatty acids Physical properties:  Water solubility:  Melting point  Isomerism Chemical properties: Soap formation Ester formation  Oxidation Hydrogenation Halogenation
  • 63. Biological importance / functions of fatty acids  Metabolic fuel : When oxidized , they form ATP  Participates in synthesis of  PL  GL  Cholesterol ester  FA derivatives act as intracellular messenger. e.g. PG  Risk of atherosclerosis & CAD:  SFA & trans FA increase LDL & decrease HDL, so the risk of CAD increases.  UFA decreases LDL, so the risk of CAD decreases
  • 64. 1. Linoleic acid : 18 C ω6 fatty acid with 2 double bonds 2. Linolenic acid : 18 C ω3 fatty acid with 3 double bonds Arachidonic acid : 20 C ω6 fatty acid with 4 double bonds [Semi essential as can be synthesized from Linoleic acid] Functions: - Component of biological membrane & maintain its fluidity - Precursor of Eicosanoids - Helps in Gonadal function, reproduction, Vision, Growth - Reduce plasma cholesterol by increasing its excretion via bile & its oxidation to bile acid Essential Fatty Acids (PUFA)
  • 65. Deficiency of EFA:  Retarded growth  Impaired gonadal function & reproductive failure  Dermatitis  Degenerative changes in arterial wall  Fatty liver  Poor wound healing & hair loss  Faulty vision Sources of EFA:  Vegetable oil (Except coconut oil and palm oil)  Fish oil (Linolenic acid rich)  Cod liver oil (Linoleic acid rich)
  • 67.  A 27 C Amphipathic lipid containing steroid nucleus  Steroid nucleus :  Cyclopentano perhydro phenatherene nucleus  A 19 C compound made of 4 fused non aromatic hydrocarbon rings (A, B, C, D)  Two methyl groups denoted as C18 and C19  Steroid nucleus is attached with - One OH group at C3 - A branched chain of 8 carbons at C17  A double bond between C5 and C6
  • 68. Functions of cholesterol:  Constituent of biological membrane  Precursor of: Steroid hormones  Bile acid , bile salts  Vitamin D  High plasma level of cholesterol is associated with atherosclerotic disorders like - Stroke - Coronary artery disease etc Sources of Cholesterol:  Endogenous synthesis  Exogenous / Dietary: Only from animal foods . e.g. egg yolk, liver, mutton, prawn, beef etc
  • 69. “All sterols are steroids but all steroids are not sterols” Steroid substances: Steroid nucleus + one oxygen atom at C-3 position of nucleus. e.g. Cortisol, Aldosterone, Testosterone etc Sterol compounds: Steroid nucleus + one hydroxyl group at C-3 position of nucleus. e.g. Cholesterol, Bile acid, Vitamin D etc
  • 70.
  • 72.  Signaling molecules derived from made by oxidation of 20 C PUFA (eicosanoic acid ) Or Prostaglandins and related compounds
  • 73.
  • 74. Name of the eicosanoids Eicosanoid includes:  Prostaglandins (PG)  Prostacyclin (PG-I2)  Thromboxane (TX)  Leukotrienes (LT)  Lipoxins (LX) Prostanoid
  • 75. Justify, “Prostaglandins are local hormones”  They act on target cells close to their site of formation to produce specific effects  They are rapidly degraded, so they are not transported to distal sites within the body
  • 76. Justify, “Prostaglandins are not true hormones” Points PG True hormones Origin Almost all tissues Specialized glands Site of action Locally Distant sites Transport via blood Not transported Transported Action on parent cells Yes No Synthesis & storage Synthesis as per need & not stored in tissues Not such
  • 77. Clinical use of Prostaglandins  Control of :  Inflammation by suppression of PG synthesis  Hypertension (PG E2 & PG I2)  Relief of asthma and nasal congestion: PG E2  To prevent :  Peptic ulcers by decreasing HCl secretion (PG E2) and treatment as well  Thrombotic events (PG I2)  Control of hypertension: PG E2 & PG I2
  • 79.  Water-soluble derived lipid  Metabolic products that are produced in excess during excessive breakdown of fatty acid  Freely transportable form of acetyl units (don’t need to be with LP /albumin for transportation in blood)  Acetoacetate, Beta hydroxy butyrate, and acetone are often referred to as ”Ketone bodies”  “Acetoacetate” is the primary ketone body.
  • 80.
  • 83. Alternate sources to glucose for energy Production of ketone bodies under conditions of cellular energy deprivation Utilization of ketone bodies by the brain