What is Lipid
• Lipids: insoluble in water, but soluble in organic solvents
including diethyl ether, chloroform, methylene chloride,
and acetone
– Amphipathic: hydrophobic in nature
• Lipids include:
– Open Chain forms
– fatty acids, triacylglycerols, sphingolipids,
phosphoacylglycerols, glycolipids,
– lipid-soluble vitamins
– prostaglandins, leukotrienes, and thromboxanes
• Cyclic forms
– cholesterol, steroid hormones, and bile acids
Lipid: Structure
1. Open chain:
O
eg. A fatty acid
OH
– long nonpolar tail with a polar head
– Saponifiable
C
2. Cyclic forms/Fused ring:
- based on the steroid ring
skeleton
A
B
D
LIPID: CLASSESS
1.
2.
3.
4.
5.
6.
Fatty acids and their derivatives
Triacylglycerols
Phosphoacylglycerol, phosphoglycerides
Sphingolipids
Wax esters
Isoprenoids (based on isoprene structure)
LIPID: Structural features
/ phosphoacylglycerol
GENERAL
STRUCTURE
The structural features of storage and membrane lipids. (a) The storage lipids are composed
of nonpolar triacylglycerol. (b) The membrane lipids are composed of glycerophospholipids
and sphingolipids which have polar and nonpolar regions
Fatty Acids
• Fatty acid: a molecule with a carboxyl group as the polar end
and a hydrocarbon chain as the hydrophobic/nonpolar end.
• an unbranched-chain carboxylic acid, mostly in even numbers of
carbon
Nonpolar hydrophobic tail
Polar hydrophilic head
Fatty Acids
• derived from hydrolysis of animal fats, vegetable oils, or
phosphodiacylglycerols of biological membranes
• Amphiphatic
Nonpolar hydrophobic tail
Polar hydrophilic head
Fatty Acids
• Length of fatty acid plays a role in its chemical
character
• Usually contain even numbers of carbons (can contain
odd, depending on how they are biosynthesized)
• FA - C=C bonds, are unsaturated fatty acid
- C-C bonds, are saturated fatty acid
Fatty Acids
Fatty Acids
• Unsaturated fatty acids have lower melting
points than their saturated counterparts; the
greater the degree of unsaturation, the lower the
melting point
Fatty Acids
• In most unsaturated fatty acids, the cis isomer
predominates; the trans isomer is rare
16:19
Palmitoleic acid
Cis double bond results
in a bent chain and lower mp.
Fatty Acids
Palmitoleic 16:19 – degree of unsaturation
or abbreviation symbol
CH3(CH2)5CH=CH (CH2)7COOH – chemical
formula
7
9
5
3
1
11
13
15
Palmitoleic acid
Fatty Acids
Stearic acid
Oleic acid
18:0
18:19
structure
Fatty Acids
Fatty Acids - examples
1. Stearic
18:0
CH3(CH2)16COOH
2. Oleic acid
18:19 / 18:19 / 18:1- 9
CH3(CH2)4CH2CH2CH2CH=CH(CH2)7COOH
3. Palmitoleic
16:19
CH3(CH2)5CH=CH (CH2)7COOH
4. Linolenic
18:29,12
CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH
5. Arachidonic 20:45,8,11,14
CH3(CH2)3(CH2CH=CH)4(CH2)3 COOH
Triacylglycerols
• Triacylglycerol (triglyceride): an ester of glycerol
with three fatty acids
• Nonpolar class of lipid, very hydrophobic
O
CH2O C R1
Glycerol
O
part
CH O C R2
O
CH2O C R3
Fatty acid
chains
Triacylglycerols (TAGs)
• TAGs which are solids at room temperature are rich
in saturated acids and are called fats.
• TAGs which are liquids at room temperature are rich
in unsaturated acids and are called oils.
– e.g. oil seeds include peanut, corn, safflower,
palm, olive and soybean.
Triacylglycerols (TAGs)
• Hydrolysis of TAGs will produce 1 glycerol and
3 fatty acids.
• Biologically this is done by lipases.
• Chemically base hydrolysis is called
saponification.
Hydrolysis of Triacylglycerols
(TAGs)
Saponification
CH2OH
O
CH2O C R3
CH OH
O
3 NaOH
CH
OH
2
CH O C R3
O
+
O
CH2O C R3
3 NaO C R3
a soap, Na or K
salt of a fatty acid
Saponification – reactions of triacylglycerol
with … to produce … , which is the sodium
salt
Phosphoacylglycerols
(Phospholipids)
O
CH2O C
O
CH O C
O
CH2O P
O
Phosphatidic acid
R1
R2
• When one alcohol group of glycerol is
esterified by a phosphoric acid rather
OH than by a carboxylic acid, phosphatidic
acid produced
• Phosphatidyl ester = phosphoacylglycerol
1 glycerol bonded to 2
fatty acids + phosphate
group
Phosphoacylglycerols =
glycerophospholipids
• Phosphoacylglycerols –
amphiphatic, polar,
hydrophilic
• The second most
abundant group of
naturally occurring
lipids, and they are
found in plant and
animal membranes
Phospholipids
second alcohol
Phosphatidyl esters = phosphoacylglycerol =
glycerophospholipids
O
CH2O C R1
O
CH O C R2
O
CH2O P OR
O
Fatty acid
R=
+
CH2 CH2 NH3
phosphatidylethanolamine
CH2 CH2 N(CH3)3
phosphatidylcholine
(lecithin)
+
O
O
OH
CH2 CH CH2 O P O CH O C R3
O CH2 O C R4
O
diphosphatidylglycerol
• Functions of phospholipids:
 as
 participate in the transduction of biological
signals across the membrane
 as
 play an important role in the
 important source of acetylcholine (common
neurotransmitter substance occur in mammals)
Phospholipids
 Salts of fatty acid with polar
head and a single nonpolar
assemble into spherical
structures - micelles

glycerophospholipids & sphingolipids
have a polar head & 2 hydrophobic
tails

Extra space taken by the non-polar
tails, these lipids unable to assemble
into micelles

So, bilayer is form - nonpolar side
combines by hydrophobic interactions
to exclude water in the centre region of
bilayer
Sphingolipids
• No glycerol
• Contain sphingosine, a
long-chain amino alcohol
• Found in
• Abundant in nervous
system
• Bares structural similarity
to phospholipids
Sphingolipids
(simplest)
Primary alcohol
group esterified to
phosphoric acid
which esterified to
choline
Sphingolipids + sugar residue =
Glycolipids
• Glycolipid: a compound in
which a carbohydrate is bound
to an -OH of the lipid
• In most cases, sugar is either
glucose or galactose
– many glycolipids are derived
from ceramides
• Glycolipids with complex
carbohydrate moiety that
contains more than 3 sugars are
known as gangliosides
glycosphingolipid
Ganglioside
Most complex
glycosphingolipid
Waxes
• A complex mixture of esters of long chain carboxylic acids (fatty acids) and
alcohols
• Found as protective coatings for plants
and animals
Steroids
• Steroids: a group of
lipids that have
fused-ring structure
of 3 six-membered
rings, and 1 fivemembered ring.
• Most abundant
steroid:cholesterol
• E.g.: vit D,
estrogen, cortisone
Cholesterol
• The steroid of most interest in our discussion of
biological membranes is cholesterol
• Amphiphilic –
but more hydrophobic than
glycerophospholipids
and sphingolipids
OH
CH3
CH3
CH3
C O
progesterone
CH3
O
testosterone
O
CH3
Phytosterol
• Plant steroid
Isoprenoids
• Based on isoprene structures
Vitamins E, K,
-carotene
Example
isoprene
Eicosanoids
Eicosanoids
• a family of compounds that have the 20-carbon
skeleton
• Arachidonic acid as precursor
• Example: prostaglandins and leukotrienes
Lipid soluble vitamins
Lipid: Functions
1.
2.
3.
4.
Storage molecules for energy
Membrane components
Messenger
Mediate the hormonal responseand synthesis of hormones
Fluid-mosaic model