lipids
*The lipids are a heterogeneous group of compounds,
including fats, oils, steroids, waxes, and related
compounds, which are related more by their physical
than by their chemical properties.
*They have the common property of being
(1) relatively insoluble in water .
(2) soluble in nonpolar solvents such as ether and
chloroform.
*Lipid is not polymers.
Lipid Functions
• Storage form of energy .
• Thermal Insulation .
• Protection for delicate organs .
• Key component of cell membranes .
• Precursors of steroid hormones as sex
hormones .
Classification of lipids
1. Simple lipids: Esters of fatty acids with various alcohols.
a. Fats: Esters of fatty acids with glycerol. Oils are fats in the
liquid state.
b. Waxes: Esters of fatty acids with higher molecular weight
monohydric alcohols.
2. Complex lipids: Esters of fatty acids containing other
groups in addition to an alcohol and a fatty acid.
a. Phospholipids: Lipids containing, in addition to fatty acids
and an alcohol, a phosphoric acid residue. They frequently
have nitrogen containing bases and other substituent, eg, in
glycerophospholipids the alcohol is glycerol and in
sphingophospholipids the alcohol is sphingosine.
b. Glycolipids (glycosphingolipids): Lipids containing a
fatty acid, sphingosine, and carbohydrate.
c. Other complex lipids: Lipids such as sulfolipids
and aminolipids. Lipoproteins .
3. Precursor and derived lipids: These include fatty acids,
glycerol, steroids, other alcohols, lipid-soluble vitamins,
and hormones.
* Acylglycerols (glycerides),cholesterol, and cholesteryl
esters (because they are uncharged ) are termed neutral
lipids.
* Even chain fatty acids are common, odd chain
fatty acids are rare, but 3 ‘C’ & 5 ‘c’ are common.
* Fatty acids with 14 – 20 Carbon are commonly seen
in natural lipids.
* Saturated Fatty acids do not contain double bond
ex. Palmitic acid.
Unsaturated Fatty acids contain one or more double
bonds.The double bond is always in cis configuration .
One double bond – Mono Unsaturated ex. Oleic acid
Two or more double bonds – Poly unsaturated fatty
acids ex. Linoleic acid Linolenic acid Arachidonic acid
ESSENTIAL FATTY ACIDS :
*The fatty acids which are not synthesized in
the body and they should be supplied in the
diet are known as Essential Fatty Acids.
*All are PolyUnsaturated Fatty Acids eg. Linoleic
acid , Linolenic acid Arachidonic acid .
Fatty acid composition of three food fats. Olive oil, butter, and beef fat consist of mixtures
of triacylglycerols, differing in their fatty acid composition.
The melting points of these fats—and hence their physical state at room temperature (25
C)—are a direct function of their fatty acid composition.
Olive oil has a high proportion of long-chain (C16 and C18) unsaturated fatty acids, which
account for its liquid state at 25 C.
The higher proportion of long-chain (C16 and C18) saturated fatty acids in butter increases
its melting point, so butter is a soft solid at room temperature.
Beef
fat, with an even higher proportion of long-chain saturated fatty acids, is a hard solid
Triacylglyerol
Fats : triglycerides which are solid at room
temperature ( most saturated triglycerides, e.g.
beef, fat, or lard)
Oils : triglycerides which are liquid at room
temperature ( most triglycerides with several
unsaturation, e.g. corn oil, peanut oil, or fish oils)
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Triacylglycerols
- Triacylglycerols are esters of glycerol with fatty acids .
- Fats and oils that are widely distributed in both plants &
animals are chemically triacylglycerols.
a) SIMPLE TRIACYLGLYEROLS - All the three fatty acids
are same type .
b) MIXED TRIACYLGLYCEROLS Contains 2-3 different
types of fatty acids , more common .
Triglycerides
O
O
O
O
O
R
O
OH
OH
OH
O
R
R
R
O
R
O
R
O
MONOGLYCERIDE
O
DIGLYCERIDE
Function: storage of energy
O
TRIGLYCERIDE
Structure of triglycerides
WAXES
* Biological waxes are esters of long-chain (C14 to C36)
saturated or unsaturated fatty acids with long-chain (C16 to C30)
alcohols.
* Their melting points (60 to 100 C) are generally higher than those of
triacylglycerols.
* Waxes serve a diversity of other functions related to their waterrepellent properties and their firm consistency.
O
H3C
(CH 2)14
C
O
CH 2
(CH 2)28-CH 3
fatty acid
long chain alcohol
Triacontanoylpalmitate, the major component of beeswax, is an
ester of palmitic acid with the alcohol triacontanol.
A honeycomb, constructed of beeswax, is firm at
25C and completely impervious to water
* In plankton, the free-floating microorganisms at the bottom of
the food chain for marine animals waxes are the chief storage
form of metabolic fuel.
* Certain skin glands of vertebrates secrete waxes to protect hair and
skin and keep it pliable, lubricated and waterproof.
* Birds, particularly waterfowl, secrete waxes from their preen glands to
keep their feathers water-repellent.
*
The shiny leaves of many tropical plants are coated with a thick layer of
waxes, which prevent excessive evaporation of water and protects
against parasites.
* Biological waxes find a variety of applications in the pharmaceutical,
cosmetic, and other industries. They are widely used in the manufacture
of lotions, ointments, and polishes.
Phospholipids
- Phospholipids are compound lipids containing Glycerol ,Fatty
acid ,Phosphate and other groups .Two Classes :
1-Glycerophospholipids In this group alcohol is glycerol .
2- Spingophospholipids In this group alcohol is sphingosine .
Glycerophospholipids :
- Glycerophospholipids Major lipids in Biological membrane .
- Glycerol – 3-phosphate is esterified with 2 Fatty acids usually c1 is
esterified with Saturated Fatty acid, and C2 is esterified with
unsaturated fatty acid.
1. Phosphatidic acid :
1. Phosphatidic acid is simplest phospholipid .
THE PRINCIPLE CLASSES OF STORAGE AND
MEMBRANE LIPIDS
All these lipids have either glycerol or sphingosin
as the backbone.
■ The
sphingolipids contain sphingosine, a long
chain aliphatic amino alcohol, but no glycerol.
-Sphingomyelin has, in addition to phosphoric
acid and choline, two long hydrocarbon chains,
one contributed by a fatty acid and the other
by sphingosine.
■ The polar lipids, with polar heads and nonpolar
tails, are major components of membranes.
- The most abundant are the glycerophospholipids
which contain fatty acids esterified to two of
the hydroxyl groups of glycerol, and a second
alcohol, the head group, esterified to the third
hydroxyl of glycerol via a phosphodiester bond.
- Other polar lipids are the sterols.
■ Glycerophospholipids differ in the structure of
their head group; common glycerophospholipids
are phosphatidylethanolamine and phosphatidylcholine.
The polar heads of the glycerophospholipids carry
electric charges at pH near 7.
* Glycolipids are composed of amino alcohol
sphingosine + long chain fatty acid +
monosaccharide unites .
* Glycolipids are important constituents of
nervous tissue such as brain and the outer
leaflet of the cell membrane
Cell membrane
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Steroids
* Steroid nucleus consists of four fused rings .
* Sterols have steroid nucleus and a hydroxyl
group
* Sterols are structural lipids present in the
membranes of most eukaryotic cells.
* Cholesterol, the major sterol in animal, is both
a structural component of membranes and
precursor to a wide variety of steroids.
Cholesterol
17
12
13
11
1
9
D
C
10
2
A
14
B
3
4
5
16
15
8
7
6
Steroid nucleus
Cholesterol, an amphipathic lipid, is an important component of
membranes.
It is the parent molecule from which all other steroids in the body,
including major hormones such as the sex hormones, D vitamins,
and bile acids, are synthesized.
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Combination of Biomolecules
• Lipoproteins (blood transport molecules)
• Glycoproteins (membrane structure)
• Glycolipids (membrane receptors)
Protein Hybrids
• Lipoproteins :in membranes and transportation of
materials
• Glycoproteins : antibodies, cell surface proteins
• Nucleoproteins : ribosomes
Nucleic Acids
DNA & RNA
• Two types :
• - Deoxyribonucleic acid (DNA)
• - Ribonucleic acid (RNA)
• Made of polymer of nucleotides joined
together by phosphodiester bond
DNA & RNA function
• DNA carries and transmits the genetic
information .
• RNA carry the genetic information from
nucleus to cytoplasm for protein synthesis .
• RNAs are involved in most steps of gene
expression and protein biosynthesis.
Base + sugar
Nucleoside
phosphoester bond
glycosidic bond
Nucleotides
■ A nucleotide consists of a nitrogenous base
(purine or pyrimidine), a pentose sugar, and
one or more phosphate groups.
Nucleic acids are polymers of nucleotides,
joined together by phosphodiester linkages
between the 5’- hydroxyl group of one
pentose and the 3’- hydroxyl group of the
next.
Nucleotides function as energy transfer
molecules : ATP , Cyclic AMP , NAD & FAD
A Nucleotide
Adenosine Mono Phosphate (AMP)
OH
Phosphate
HO
H+
Nucleotide
P
O
Base
N
H
O
5’
NH2
H
N
CH2
4’
3’
O
1’
Sugar
OH
2’
HOH
N
N
Nucleoside
Purines
Adenine
N
N
O
NH2
CH3
N
NH2
Uracil
(RNA)
NH
Guanine
NH
N
Thymine
O
(DNA)
N
N
O
N
N
Pyrimidines
NH
O
N
O
NH2
Cytosine
N
N
O
Polynucleotide Formation
Dehydration reaction to form
phosphodiester bond
Phosphodiester linkages in the covalent backbone of DNA and RNA.
The phosphodiester bonds link successive nucleotide units.
The backbone of alternating pentose and phosphate groups in both types of
nucleic acid is highly
DNA STRUCTURE
two polynucleotide chains are twisting around each
other in the form of a double helix
• The two strands are complementary & anti-parallel
• Wound around each other in a rightward direction
• stabilized by H-bonding between bases in adjacent
strands.
• The bases are in the interior of the helix
• Purine bases form hydrogen bonds with
pyrimidine.
Sugar phosphate backbone of
DNA
5’Phosphate group
P
HO
NH2
O
N
O
OH
N
N
CH2
H
N
O
O
CH2
O
HO
P
O
O
N
O
CH2
HO
P
O
H
O
OH
H
H2O
NH
N
NH2
N
O
O
CH2
O
H
P
NH2
O
HO
P
O
H
O
H
N
O
O
CH2
O
P
HO
H
O
OH
5’Phosphate
group
HO
CH2
3’Hydroxyl group
H2O
N
O
O
HO
O
D
N
A
3’Hydroxyl group
OH
5' C-G-A-T-T-G-C-A-A-C-G-A-T-G-C 3'
| | | | | | | | | | | | | | |
3' G-C-T-A-A-C-G-T-T-G-C-T-A-C-G 5'
Base Pair Rule
• Adenine always base pairs with Thymine
(or Uracil if RNA)by two hydrogen bonds .
• Cytosine always base pairs with Guanine
by Three hydrogen bonds .
Base Pairing
Guanine And Cytosine
-
+
+
+
-
Base Pairing
Adenine And Thymine
+ -
Adenine
-
+
Thymine
Base Pairing
Adenine And Cytosine
+
-
-
Base Pairing
Guanine And Thymine
+
+
RNA
• Single strand of polynucleotides .
• Purine bases are A & G , prymidines are C & U.
• In viruses it can carry out DNA role
* What are the differences in structure and function
between DNA & RNA ?