lipids summary for biochemistry

1. lipids sheet
done by: dawood alatefi

2. Lipids
Definition:
Lipids are naturally occurring organic molecules that are nonpolar and therefore dissolve in
nonpolar organic solvents but not in water. They are defined by their physical behavior rather
than their chemical structure(like amino acids and carbohydrates), so that we may find a great
variety of chemical structures among the lipid class of molecules.
Major role of lipids(lipid function):
 Energy storage from metabolism of food within fat cells (adipocytes).
 The amphipathic lipids form the cell membrane which Separate the inside and outside
of the cells.
 Chemical messengers and vitamins.
 Thermal insulation and protective padding
Classification of lipids: Lipids
Fatty Acids Glycerides
Complex lipids
Saturated Phosphoglycerides
Non-glycerides
Unsaturated
Neutral
Glycerides
Waxes Sphingolipids Steroids
Lipoproteins
Glycolipids
Animal steroids= cholesterol
Plant steroids

3. we can classify the lipids according to the foundation molecule they have into three categories.
(1)The first is the Fatty acid: which is composed of carboxylic acid group connected to a
hydrocarbon chain(R chain). And depending on whether this chain have single bonds or double
bonds between carbons atoms, we can classify fatty acids into saturated or unsaturated fatty
acids respectively.(2) The second category is Glycerides: which have the glycerol molecule as
the foundation group. This glycerol molecule is esterified with different fatty acids to form
different kinds of glycerides( here the fatty acids itself is the R group).when the three hydroxyl
groups of the glycerol molecule are esterified with three fatty acids we get neuteral glycerides
which are nonpolar(hydrophobic) and these neuteral glycerides are known as triacylglycerols.
But when only two hydroxyl groups of the glycerol are esterified with two fatty acids and the
third is esterified with phosphate group we get another type of Glycerides which are
phosphoglycerides which are known as phosphoglycerols.(3) The third category is Non-
glycerides:which contain the rest of lipids with different foundation groups, such as (A)waxes:
which is a mixtures of esters and (B) sphingolipids: which have sphingosne as its foundation
group and (C) Steroids: which have a fused-ring system of three six-membered rings and one
five-membered ring as the foundation group for all steroids.(4) the fourth category is
Complex lipids: which is a complex of lipids and proteins(lipoproteins), or a
complex of lipids and carbohydrates(glycolipids).
 Fatty acids:
Saturated & unsaturated
Definition: Fatty acids are biomolecules containing a carboxyl functional group (-COOH)
connected to an unbranched aliphatic chain(hydrocarbon chain). These structural features give
them a split personality: one end is polar and sometimes ionic(the carboxyl group), whereas the
opposite end (the hydrocarbon chain) has nonpolar properties, so that it is amphiphilic, but
overall they are hydrophobic
because the long
hydrocarbon chain compared
to carboxyl group.
1

4. physical and chemical properties of fatty acids:
1) Most have even numbers of carbon atoms.
2) May or may not contain carbon carbon double bonds.
3) Saturated fatty acids (without double bonds)
4) Unsaturated fatty acids (with double bonds)
5) Fatty acids containing one double bond are termed monounsaturated fatty acids
whereas fatty acids containing more than one double bond are termed polyunsaturated
fatty acids.
6) The stereochemistry at the double bond is usually cis rather than trans
7) Soluble in organic solvents
8) Smaller chains (2:0 ; 3:0 ; 4:0) are more soluble ,decrease in solubility with chain length.
9) Saturated fatty acids > 10 are solid at room temperature
10) Saturated fatty acid <10 and all unsaturated fatty acid are liquid at room temperature
11) Larger fatty acid are insoluble in water but they appear to dissolve in dilute aqueous
NaOH or KOH solutions, this is because an acid-base reaction take place forming the Na+
or K+
salt of the acids. The Na+
or K+
salts of fatty acids are called soaps. The soaps
appear to dissolve In water, but they do not form true solutions. The amphiphilic
molecules aggregate into molecular arrangements called micells.
common fatty acids:
you need to memorize the name of each acid and its number of carbons atoms and its
melting point. You also have to know how many double bonds for unsaturated fatty acids.
Acid Number of
carbon atoms
Formula Melting point( C)
Lauric 12 CH3(CH2)10COOH 44
Myristic 14 CH3(CH2)12COOH 58
palmitic 16 CH3(CH2)14COOH 63
Stearic 18 CH3(CH2)16COOH 71
Arachidic 20 CH3(CH2)18COOH 77
Typical Naturally Occurring Saturated Fatty Acids

5. Acid Number
of Carbon
Atoms
Degree of
unsaturation
Formula Melting
point( C)
Palmitoleic 16 16:1-∆
9
CH3(CH2)5CH CH(CH2)7COOH
-0.5
Oleic 18 18:1-∆
9
CH3(CH2)7CH CH(CH2)7COOH
16
Linoleic 18 18:2-∆
9,12
CH3(CH2)4CH CH(CH2)CH CH(CH2)7COOH
-5
Linolenic 18 18:3-∆
9,12,15
CH3(CH2CH CH)3(CH2)7COOH
-11
Arachidoni
c
20 02:4-∆
5,8,11,14
CH3(CH2)4CH CHCH2CH CHCH2CH CHCH2CH CH(CH2)3COOH
-50
02:4-∆5,8,11,14
from the previous two tables you can notice the following
1) Melting point decrease with the presence of more double bonds fatty acid has.
2) Vegetable oils are lower melting than animal fats because oils have more unsaturated
fatty acids than animal fats.
 Triacylglycerols(TAGs)
Triacylglycerols are trimesters of glycerol with three fatty acids.
•Glycerol
(glycerine) is
The position of double bonds from the carboxyl end of the molecule
Number of double
bonds
Number of
carbon atoms
Typical Naturally occurring Unsaturated fatty acids
2

6. 1,2,3-propanetriol
•The 3 fatty acids can be the same or different.
• The reaction between glycerol and each fatty acid is a dehydration reaction in
which we lose one H2O molecule.
All fats and oils are composed of triacylglycerols. Triacylglycerols isolated from
animal tissues are called fats and are solids at room temperature because they
contain predominantly saturated fatty acids. And triacylglycerols isolated from
plant seeds are called oils and contain predominately unsaturated fatty acids.
Chemical Reactions of TAGs:
1) Hydrogenation:

7. 2) Hyrolysis: Hydrolysis of triacylglycerols occurs under physiological
conditions and the catalysts are enzymes called Lipases. These enzymes are
present in the intestines and in fat cells( adipocytes), where they release
fatty acids for energy metabolism
3) Saponification: each ester of TAG is hydrolyzed in a reaction catalyzed by
NAOH to produce glycerol and soaps:
 Phosphoglycerols (Phosphatidyl esters) (Glycerophospholipids)
The foundation molecule for the glycerophospholipids is 1,2-diacylglycerol-3-phosphate,which
has the generic name phosphatidic acid.(this means that Phosphoglycerols consist of two acyl
groups (two fatty acids) linked to carbon1 and carbon 2 of glycerol, and one phosphate group
linked to carbon3 of glycerol. The structure of phosphatidic acid is shown to the wright.
Regardless of R1 and R2 this is called phosphatidic acid when phosphate group is not linked to
any R group. Phosphoric acid is triprotic and thus can form more than one ester linkage and
different R groups result in different types of phosphoglycerols.
3

8. the first and second hydroxyl groups of glycerol is esterified by to fatty acids and the third
hydroxyl group is esterified by phosphoric acid. And because phosphoric acid is triprotic, it is
able to react with up to three alcohol moieties to form mono-,di-, and trimesters,but in
glycerophospholipids the second alcohol of phosphate is esterified with different alcohols .now
depending on the type of alcohol which will be esterified with the second alcohol of phosphate
we get different types of phosphoglycerols as follow:
Name of X Structure of X Name of glycerophosphlipids
(a) Hydrogen -H Phosphatidic acid
(b) Ethanolamine CH2 CH2 N+
H3 Phosphatidylethanolamine
(Cephalin)
(c) Choline CH2 CH2 N+
(CH3)3 Phosphatidylcholine
(lecithin)
(d) serine CH2 CH N+
H3
COO-
Phosphatidylserine
(e) Inositol
Phosphatidylinositol

9. (f) Glycerol Phosphatidylglycerol
(f) Phosphatidyl-
glycerol
CH2CH
OH
CH2 O P
O
O-
O CH2
R4COCH
O CH2OCR3
O
Diphosphatidylglycerol
(Cardiolipin)
The previous phosphoglycerols are named by combining “Phosphatidyl” with the
alcohol name.This We should by now see a major structural difference when
comparing triacylglycerols and glycerophospholipids. Triacylglycerols are
nonpolar and hydrophobic.The glycerophospholipids, on the other hand, have
highly polar and sometimes electrically charged regions on the molecule in
addition to nonpolar regions. Therefore, we can distinguish two structural
features in the glycerophospholipids: a polar head and nonpolar tails. These
characteristics are essential for membrane structure.
Sphingolipids
A second group of polar lipids found in membranes are the sphingolipids. This
major class of lipids is represented by three subclasses: ceramides,
sphingomyelins, and glycosphingolipids(Glycolipids).Here the foundation
molecule is sphingosine.0
Found almost exclusively in the
inner mitochondrial membrane
4

10. HO
H
C C
H
HC
C
H
(CH2)12 CH3
H
N
H2C
H
OH
HO
H
C C
H
HC
C
H
(CH2)12 CH3
H
N
H2C
C
OH O
R
HO
H
C C
H
HC
C
H
(CH2)12 CH3
H
N
H2C
C
O O
R
X
Sphingosine
Ceramide
General Structure of Sphingolipids

11. Name of X Structure of X Name of
Sphingolipid
Notes about it
(a) Hydrogen -H Ceramide
(b)phosphocholine
P
O
O
O-
CH2CH2N+(CH3)3
Sphingomyelin
Although
the sphingomyelins are found
in plasma membranes,
they are probably best
known and named for
their presence in the myelin sheath
, where they insulate nerve axons.
(c) Glucose
O
OH
OH
OH
CH2OH
HOH
Glucocerebroside
Glucocerebroside & Galactocerebroside
are Called Cerebrosides or Glycolipids
and they are abundant
in the memberanes
of the brain and nervous system
(d) Galactose
O
OH
OH
OH
CH2OH
HOH
Galactocerebroside
(e) Complex
sugar
Oligosaccharide
(>3 sugars)
H
GlucoseGalactose
Sia
Ganglioside
Gangliosides are present in
large quantities in nerve
tissues

12. the amino group at C2 of sphingosine may be linked via an amide bond with a fatty acid. The
resulting molecule is called a ceramide and has a polar head(hydroxyl group on C1 of
sphingosine) and two nonpolar tails . Another class of sphingolipids uses the amino and
hydroxyl groups to link additional units. The sphingomyelins, the only phosphorus-containing
sphingolipids, contain a fatty acid on the
amino group and a phosphocholine unit esterified with thehydroxyl group at C2 of ceramide. A
third subclass of the sphingolipids is represented by the glycosphingolipids.
These carbohydrate-containing lipids use the ceramides as foundation molecules. The
cerebrosides consist of ceramide with a monosaccharide unit in glycosidic linkage at
the hydroxyl group at C1 of sphingosine . The carbohydrates commonly
found are glucose, galactose, and N-acetylgalactosamine. The most complex sugar-containing
lipids are the gangliosides , which are composed of several carbohydrate units linked by
glycosidic bonds.
Polar lipids and membranes:
We have finished talking about polar lipids which are Glycerophospholipids and sphingolipids.
In spite of chemical differences, these molecules serve a similar biological role as structural
units in membranes. Their similar features, a polar region and a nonpolar region, endow them
with their common biological characteristic. We have observed that salts of fatty acids with a
polar(ionic) head and single nonpolar tail assemble spontaneously into spherical structures
called micelles. The polar lipids represented by the glycerophosphlipids and sphingolipids each
has a polar(and sometimes ionic) head and two hydrophobic tails. Because of the ex…. Space
taken by the nonpolar tails, these lipids are unable to assemble into micelle. Instead, they form
bilayers, composed of two monolayers or sheets of polar lipids. The nonpolar side of each sheet
sphingosine
ceramides sphingomyelins glycosphingolipids(Glycolipids)
Glucocerebroside Galactocerebroside
GangliosidesCerebrosides

13. combines by hydrophobic interactions to exclude water in the central region of the bilayer. The
bilayer provides a structural framework for membrane assembly.
 Waxes:
Waxes are complex mixtures of esters of long chain carboxylic acids and long chain alcohol. An
example of waxes is beeswax which is a protective coating on most fruits, aquatic birds feathers,
etc.
 Steroids:
Steroids are group of polar lipids. The steroids all have the characteristic fused-
ring system of three six-membered rings labeled A,B, and c and one five-
membered ring called the D ring. Ketones, alcohols, double bonds, and
hydrocarbon chains decorate the ring system in
various types of steroids.
the molecular structure common to all steroids
showing the four fused rings, A,B,C, and D.
cholesterol
The best known steroid is cholesterol. cholesterol has a hydroxyl group on the A
ring , a double bond in ring B, and hydrocarbon chains attached at several
locations. The most chemically reactive portion of the cholesterol structure is the
A B
C D
5
6

14. hydroxyl group. Under physiological conditions, it is common for a fatty acid to be
esterified at this position.
The steroids other than cholesterol have many roles throughout the body such as
hormone functions and acting as bile acids essential for the digestion of fats and
oils.
Cholesterol has two important functions: a component of cell membranes and it
is the starting point for biosynthesis of the steroid hormones(including sex
hormones, cortisol) and the bile acids(or bile salts) and vitamin D3.Cholesterol
has a role in the development of
Estradiol Testosterone Cortisol
CH3
CH3
CH3
OH
O
CH3
OH
H3C OH
C O
CH2OH
CH3
OH
O
CH3
CH3
OH
HO
HO
CH3
A B
C D
OH
OH
CH3
CH3
COO-
NA+
atherosclerosis

15. Two important bile acids in humans are cholic acid and its glycine
derivative,glycocholic acid. The bile salts are stored in the gallbladder and
secreted into the intestines to help solubilize, digest, and absorb dietary fats
The cholesterol molecule, which is found almost exclusively in animal tissue, is
derived from units of five carbons called isoprene(2-methyl-1,3-butadiene)
H2C C
CH3
CH CH2
 Eicosanoids(Prostaglandins & Leukotriense &Thromboxanes)
Eicosanoids are a group of compounds derived from 20-carbon, polyunsaturated
arachidonic acid(20:4). They are synthesis throughout the
body and function as local hormones(Paracrine). There are
three subclasses of eicosanoids:prostagglandins,
thromboxanes, and leukotrienes.Prostaglandins and
thromboxanes are synthesized by the cyclic pathway of
arachidonic acid metabolism, whereas the leukotrienes are produced by the linear
pathway of arachidonic acid metabolism. The cyclic pathway begins with the reaction of
arachidonic acid with oxygen, catalyzed by prostaglandin synthase
(cyclooxygenase=COX), an enzyme with two catalytic activities, oxygenase and
peroxidase. It is called cyclooxygenase because it forms the five-membered cyclic
structure (prostaglandin H2). The first important intermediate, prostaglandin H2(PGH2),
is the precursor for other prostaglandins and for the thromboxanes.
(1) Prostaglandins(PGs)
Prostaglandins contain a five-membered ring substituted with two side
chains and functional groups, including a carboxylic acid, hydroxyl groups,
ketones, and carbon-carbon double bonds. They are derived from
Arachidonic acid
7

16. arachidonic acid by the cyclic pathway. The prostaglandins were first
isolated from the prostate gland.
PGs functions:
o Are involved in the
production of pain and
fever, regulation of blood
pressure, blood
coagulation and
reproduction.
o Inhibit the aggregation of
platelets during blood
clotting
o Stimulation of smooth-
muscle contraction
o Induction of inflammation
 Cortisone and other steroids have anti-inflammatory effects because of their
inhibition of PGs synthesis.

17. Lipoxygenase
Prostaglandin synthase
O2 (Cyclooxygenase,COX)
PGG2
Peroxidase activity
PGH2 Thromboxane synthase
TXB2 TXA2
Other
Refered to page 249 in boyer book for distinguishing the differences between the three catagories structures
Arachidonic Acid
(1) Leukotrienes
Cyclic r pathway: can be inhibited by
aspirin
Cause the contraction of smooth
muscle, especially in the lungs
Linear pathway: can’t be inhibited by
aspirin
(2) Thromboxanes
(3) Prostaglandins
PGE2 PGD2
PGE2 &PGD2 have been discovered in the
brains of mammals, including humans. These
two prostaglandins are especially concentrated
in the preoptic area, the sleep center of the
brain. PGD2 promotes physiological sleep and
PGE2 induces wakefulness
Increase
blood clotting

18.  The COX enzymes:
1) COX-1 isoenzyme:
a constitutive enzyme. It is expressed in most tissues at all times. It is probably
needed for cell maintenance and has general housekeeping duties, especially in the
stomach and gastrointestinal (GI) tract.
2) COX-2 isoenzyme:
An induced enzyme synthesized in response to inflammatory stimuli such as injury
or disease.
Induction of COX-2:
The induction of COX-2 leads to elevated levels of the prostaglandins that cause the
pain and swelling associated with the inflammatory response.
Treatment:
 1: Non-steroidal anti-inflammatory drugs(NSAIDs):
This drugs is over the counter drugs(O.T.C), drugs that can be taken without a
prescription from a doctor. Some examples of these NSAIDs which can be
used for treatment of COX-2 induction include:
A- Aspirin : some relief from the pain may be achieved by taking aspirin,
which is an analgesic(painkiller), antipyretic(fever reducer), and anti-
inflammatory agent.
B- Other NSAIDs such as ibuprofen, naproxen, and indomethacin:
These NSAIDs act by inhibiting both COX-1 and COX-2, thus reducing the
production of prostaglandins.
 Side effects of NSAIDs:

19. We have mentioned previously that the NSAIDs act by inhibiting both COX-1 and
COX-2 but as you know that COX-1 is a constitutive enzyme which is probably
needed for cell maintenance and has general housekeeping duties, especially in
the stomach and gastrointestinal(GI)tract. So that means that inhibition of COX-1
by NSAIDs is going to affect its duties . So NSAIDs have undesirable side effects
such as gastric ulceration and other problems including stomach bleeding.
 2: Selective COX-2 inhibitors:
COX inhibitors are now better designe and more selective for COX-2.
Three painkilling drugs that act by inhibiting COX-2 but not COX-1 have been
approved by the FDA: Bextra, Celebrex, and Vioxx.
All three drugs are now under close scrutiny by the FDA because recent
studies have shown that the drugs may increase the risk of heart attack and
stroke.
 Epidemiological studies on COX-1 and COX-2 inhibitors have provided surprise
evidence that the drugs may prevent other diseases including some
cancers(Colorectal cancer) and Alzaheimer’s diseas.
3) COX-3 isoenzyme:
COX-3 does not activate inflammatory reactions and it is only inhibited by
acetaminophen or paracetamol(like panadol) which act as analgesic and
antipyretic.
Acetaminophen inhibits neither COX-1 nor COX-2, so it displays no measurable anti-
inflammatory action.
(2)Thromboxanes: Thromboxanes are six-membered ring containing oxygen
( they contain cyclic ethers). They are also derived from arachidonic acid
by the cyclic pathway. The thromboxanes were first isolated from blood
platelets (thrombocytes), where they are thought to facilitate the
formation of blood clots. An
example of thromboxanes is
thromboxane A2(TXA2) which

20. induce platelet aggregation and smooth muscle contraction.
(3)Leukotrienes (LK):
The leukotrienes are derived from arachidonik acid by the linear pathway.
This biosynthetic route is initiated by enzymes called lipoxygenases which
catalyze oxygenation(but not cyclization) of arachidonic acid. The
leukotienes were first isolated from white blood cells (leukocytes). The
structural characteristics that separate leukotrienes from other
eicosanoids are the linear chain(no rings) and the presence of three
conjugated double bonds. Asthmatic attacks and allergic reactions to
pollens may be caused by overproduction of leukotrienes. Drugs that
inhibit the synthesis of leukotrienes or block its receptors are used in the
treatment of asthma.
 Lipid-soluble(hydrophobic) Vitamins
There are two groups of vitamins, water soluble vitamins and fat soluble(lipid
soluble) vitamins. This lipid-soluble group of vitamins are derived from isoprenes so
they can be classified as terpenes, but because of their importance in human health
they are usually considered a separate category of lipids. The common lipid-soluble
vitamins are A, K, E, D.
Vitamin Common Name Chemical characteristics Biological function
A Retinol A terpene with 20
carbons
Absorption of light in
vision
K Vitamin K Bicyclic ring system with
long hydrocarbon chain
Regulates blood clotting;
bone formation
E α-Tocopherol Aromatic ring with long
hydrocarbon chain
Antioxidant; prevents
oxidation damage to
cellular membranes
D Several forms;
One is
D3(cholecalciferol)
Formed from cholesterol
by ultraviolet radiation
Regulation of calcium
and phosphorus
metabolism

21. Vitamin A or retinol
Vitamin A is oxidized to retinol
Retinol reacts with opsin to form rhodopsin
oo
Rhodopsin
Opsin
Vitamin K
A long unsaturated hydrocarbon side chain consist of repeating isoprene
units. The number of isoprene units determines the exact form of vitamin K.
vitamin K has a regulatory function in blood clotting. The anticoagulants,
dicumarol and warfarin(a rat poison), are vitamin K antagonists( have the
opposite function of vitamin K.
Vitamin E
Vitamin K is an antioxidant (a good reducing agent) to protect important
compounds, such as vitamin A, from degradation and to react with and
remove free radicals.
β-Carotene
Vitamine A
Retinol
Retinol
β-Carotene is the precursor of vitamin A
β-Carotene is an unsaturated hydrocarbon

22. • A free radical are very reactive because it has at least one unpaired electron
• Free radicals play a role in the development of cancer and in the aging process.
Vitamin D
• Has several forms such as, vitamin
D3 (cholecalciferol) • Vitamin D3 is
formed from cholesterol by the action
of UV radiation from the Sun • Vitamin
D3 increases a Ca2+ binding protein
synthesis that increases dietary
calcium absorption in the intestines
resulting in Ca uptake by the bones. •
Rickets
Plasmalogens
• Plasmalogens
– Phospholipids with one ether bond
– important in membranes of heart and brain
– Signaling
– Protective against reactive oxygen species
Special thanks for:
Duha atieh