Transcript Fatty acid - The Vignanam

Fatty Acids
• Fatty acids are aliphatic straight chain hydrocarbon
compounds with a terminal carboxylic group.
• They are building blocks of lipids
Methyl
• Insoluble in water
group
• Typically 12-18 carbon atoms (even number)
• Some contain double bonds
O
C – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2……. CH3
HO
Carboxyl group
Hydrocarbon chain
O
C – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2……. CH3
HO
 A typical fatty acid has a carboxyl group and hydrocarbon tail
 fatty acids with 16 and 18 carbon atoms are abundant in
nature
 there are about 200 fatty acids
 Acetic acid (CH3COOH); Palmitic acid (C15H31COOH); Stearic
acid (C17H35COOH); Oleic acid (C17H33COOH)
 they may or may not contain double bonds – fatty acids with
double bonds are called as unsaturated fatty acids and fatty
acids with double bonds are called as saturated fatty acids
O
C – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2……. CH3
HO
1
2
3
4
5
6
7
8
9
10
 The carbon atoms are numbered
In most of the unsaturated fatty acids double bond lies
between carbon atom 9 & 10. this designated as ∆9
O
C – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH= CH – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH3
HO
Oleic acid with a single double bond
 When there are more than one double bond, the additional
bond occurs between the ∆9 and the methyl terminal group
The symbol 18:0 denotes a C18 fatty acid with no double bonds.
The symbol 18:2 denotes a C18 fatty acid with two double bonds.
 similarly the symbol 18:2; 9, 12 is used to denote C18 fatty acid
with two double bonds in the 9th and 12th position.
Triglycerides (Simple lipids)
 A simple lipid is formed when three molecules of fatty
acids combine with one molecule of glycerol. In this
process 3 molecules of water are released
Tripalmitin
 Three molecules of palmitic acids combine with one
molecule of glycerol.
CH2OH - Palmitic acid
CH2-O-COC15H31
Palmitic acid
CH2OH - Palmitic acid
CH2-O-COC15H31
Palmitic acid
CH2OH - Palmitic acid
CH2-O-COC15H31
Palmitic acid
Formation of a triglyceride, as simple lipid
Tristearin
 Three molecules of stearic acids combine with one
molecule of glycerol.
CH2OH - Stearic acid
CH2-O-COC17H35
Stearic acid
CH2OH - Stearic acid
CH2-O-COC17H35
Stearic acid
CH2OH - Stearic acid
CH2-O-COC17H35
Stearic acid
Formation of a triglyceride, as simple lipid
Triolein
 Three molecules of oleic acids combine with one
molecule of glycerol.
CH2OH - Oleic acid
CH2-O-COC17H33
Oleic acid
CH2OH - Oleic acid
CH2-O-COC17H33
Oleic acid
CH2OH - Oleic acid
CH2-O-COC17H33
Oleic acid
Formation of a triglyceride, as simple lipid
Simple lipids
• When the three fatty acids of a lipid are
similar, the fat is called a neutral fat
• When the three fatty acids of a lipid are
different, the fat is called a mixed fat. Eg:
dipalmito stearin
Mono & Diglycerides
• When only one fatty acid is combined to a
glycerol, the fat is called as monoglyceride
• When two fatty acid are combined to a
glycerol, the fat is called as diglyceride
CH2OH - Palmitic acid
CH2OH
CH2OH
CH2-O-COC15H31
CHOH
CH2OH
CH2OH - Palmitic acid
CH2-O-COC15H31
CH2OH - Palmitic acid
CH2-O-COC15H31
CH2OH
CH2OH
 Lipids on hydrolysis yields glycerol and fatty acids
Lipids
Simple
lipids
Compound
lipids
Derived
lipids
 Compound lipids: contain some chemical groups in addition
to fatty acids and glycerol. Eg:
Lipid + Phosphate group : Phospholipids
Lipid + Carbohydrate
: Glycolipid
 Derived lipids: these are the hydrolyzed products of simple
and compound lipids. Eg: Steroids, Terpenes, Carotenoids
Characteristics
• Fatty acids are building blocks of lipids
• They have a single carboxyl group and a long
non-polar hydrocarbon tail (oily or greasy
nature)
• carbon atoms are numbered starting at
carboxyl terminus
O
1
2
3
4
5
6
7
8
9
10
C – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2 – CH2……. CH3
HO
α
β
ω
• carbon atom 2 & 3 are often referred to as α
and β respectively. The methyl carbon at the
last is called ω carbon.
• Fatty acids containing a single bond is called
saturated fatty acid. The suffix – anoic
indicates a saturated fatty acid
• Fatty acids containing one or more double
bonds is called unsaturated fatty acid. The
suffix – enoic indicates a saturated fatty acid
• Eg: Octadecanoic acid, Octadecenoic acid
• Phospholipids are compound lipids. They are
formed by glycerol, phosphoric acid and
fattyacids. They are also called as phosphatids.
• They are the structural components of
membranes and so are abundant in brain,
kidney,etc..
• Due to the presence of phosphoric acid group,
phospholipids behave as polar lipids.
• They are hydrophilic in nature.
• Phospholipids are amphipathic.
TYPES OF PHOSPHOLIPIDS
• Phospholipids are further classified into:
1. lecithins.
2. cephalins.
3. plasmologens.
4. phosphoinositides.
5. phosphingosides.
LECITHINS
Lecithins are the esters of glycerol with fattyacids.
•
•
• Two hydroxyl groups of glycerol are esterified by two
fatty acid molecules. The third hydroxyl group of
glycerol is esterified by a phosphoric acid molecule.
• The phosphoric acid group forms an ester with
choline (nitrogenous base).
CH2OH - Fatty acid
CH2OH - Fatty acid
CH2OH - Phosphoric acid - Choline
• These are yellowish grey solids, soluble in ether, alcohol.
• found in all animals (brain, nerve tissue, sperm and egg
yolk) and plants (seeds & sprouts).
• Lysolecithin injected into blood stream by snake bite
causes rapid rapture of red blood cells. This is called
hemolysis
CEPHALINS
 Cephalins are compound lipids. They are
otherwise called phosphatidyl ethanolamine.
These are more acidic than lecithins.
• They resemble lecithins except that the
choline is replaced by ethanolamine or serine
• They consists of 4 components namely,
glycerol, fatty acids, phosphatidyl
ethanolamine. CH2OH - Fatty acid
CH2OH - Fatty acid
CH2OH - Phosphoric acid - Ethanolamine
 PLASMOLOGENS :These resemble lecithins and cephalins except
in having one unsaturated ethen group in the place of
fatty acid group.
 PHOSPHOINOSITIDES :On hydrolysis it yields 1 glycerol, 2 molecules of
fatty acids, 1 molecule of inositol (replaces the base)
and 1/2/3 molecules of phosphoric acids
 PHOSPHINGOSIDES :In these lipids glycerol is replaced by either
sphingonise or a closely related dihydrosphingosine
which are also nitrogenous bases. It is commonly
found in nerve tissue.
GLYCOLIPIDS
 Glycolipids are compound lipids containing
sugars and high molecular weight fatty acids like
sphingosine and no phosphoric acid.
 It is found in brain, adrenals, kidney, spleen,
liver, leucocytes, thymus, lungs, retina, egg-yolk
and fish sperm.
 Gangliosides is a glycolipid found in brain tissue.
 These are found in ganglion cells of nervous
tissue and also in parenchymatous tissue like
spleen and erythrocytes.
 It contains ceramide, N-acetyl neuraminic acid (NANA), Nacetyl galactosamine, carbohydrates (hexoses).
 Gangliosides are stored in large amounts in the brain and
spleen.
 Glycolipids containing sulphur are called sulfolipids and
sulfadites.
 These are widely distributed in plants.
 It is localised in chloroplasts.
 It is also found in the chromatophores of photosynthetic
bacteria.
 It is present in the white matter of brain.
SPHINGOLIPIDS
 Sphingolipids, or glycosylceramides, are a class of lipids containing a backbone
of sphingoid bases, a set of aliphatic amino alcohols that includes sphingosine.

They were discovered in brain extracts in the 1870s and were named for the
mythological Sphinx because of their enigmatic nature.
 These compounds play important roles in signal transmission and cell
recognition.
 Sphingolipidoses, or disorders of sphingolipid metabolism, have particular impact
on neural tissue.
 A sphingolipid with an R group consisting of a hydrogen atom only is a ceramide.
Other common R groups include phosphocholine, yielding a sphingomyelin, and
various sugar monomers or dimers, yielding cerebrosides andglobosides,
respectively.
 Cerebrosides and globosides are collectively known asglycosphingolipids.
STRUCTURE
 The long-chain bases, sometimes simply known
as sphingoid bases, are the first non-transient
products of de novo sphingolipid synthesis in
both yeast and mammals.
 Ceramides and glycosphingolipids are N-acyl
derivatives of these compounds.[4]
 The sphingosine backbone is O-linked to a
charged head group such
as ethanolamine, serine, or choline.
 The backbone is also amide-linked to an acyl
group, such as a fatty acid.
TYPES
 Simple sphingolipids, which include the sphingoid bases and
ceramides, make up the early products of the sphingolipid
synthetic pathways.
 Sphingoid bases are the fundamental building blocks of all
sphingolipids. The main mammalian sphingoid bases are
dihydrosphingosine
and
sphingosine,
while
dihydrosphingosine and phytosphingosine are the principle
sphingoid
bases
in
yeast.[5][6]
Sphingosine,
dihydrosphingosine, and phytosphingosine may be
phosphorylated.
 Ceramides, as a general class, are N-acylated sphingoid
bases lacking additional head groups.
 Dihydroceramide is produced by N-acylation of
dihydrosphingosine. Dihydroceramide is found in both
yeast and mammalian systems.
 Ceramide is produced in mammalian systems by
desaturation of dihydroceramide by dihydroceramide
desaturase 1 (DES1). This highly bioactive molecule
may also be phosphorylated to form ceramide-1phosphate.
 Phytoceramide is produced in yeast by hydroxylation of
dihydroceramide at C-4.
STEROIDS
Steroids are nonsaponifiable lipids. They cannot
yield soap on hydrolysis because they do not
contain fatty acids. Compounds containing 1,2cyclopentanoperhydrophenanthrene nucleus in
their structures are called steriods.
 Steroids are derived lipids.
 The steroids separate from fat, when fat is
saponified.
 Steriods are readily soluble in ether, benzene,
chloroform, petroleum ether and acetone but
insoluble in water, acids and alkalies.
 In the presence of bile salts, they are rendered
soluble even in water.
STRUCTURE : Steroid contains four rings. They are named as A, B, C
and D. The rings A, B and C are hexagons called
cyclohexane rings and the ring D is a pentagon called
cyclopentane.
 The 3 cyclohexane rings are fused in a non-linear or
phenanthrene manner.
 The cyclopentane ring is fused terminally. This ring
system is called cyclopentanophenanthrene or
sterane.
 The numbering of carbon atoms starts from rings A to
D.
 Cholestrol, a steroid contains two angular methyl
groups, namely C-18 and C- 19. Methyl group C-18 is
attached to carbon atom number 13. Methyl group C19 is attached to carbon atom number 10. A line
above C-10 or C-13 denotes a methyl group.
 The steroids may have one or more alcoholic groups.
The steroids containing alcoholic groups are called
sterols. These are crystalline compounds containing
secondary alcoholic group.
The common steroids are cholestrol, coprostanol,
ergosterol, bile acids, androgens, oestrogens,
progesterone, adrenal corticoids...
Types
 Sterols are found in plant and animal oils.
 Sterols are classified into 3groups based on their
source of origin. They are:
1.ZOOSTEROLS :zoosterols are found in animals.
eg :- Cholesterol
2.PHYTOSTEROLS : phytosterols are found in plants.
eg :- Stigma sterols.
3.MYCOSTEROLS : mycosterols are commonly found in
yeast and fungi.
eg :- Ergosterol.