Lipid and their forms

Lipid

•Lipids are fatty acid of alcohols and related
substance which are in soluble in water but soluble
in number of no polar organic solvents such as
ether, chloroform and benzene.
•Lipids are basically made of carbon, hydrogen, and
sometimes oxygen in which the content of oxygen is
always small as compared to hydrogen and carbon.
•Many lipids contain small amount of additional
element like phosphorus, nitrogen and sulphur.
•This lipid include fats, oils, waxes and related
compound.
•The basic components of all lipids are fatty acids.

 1.Simple lipid

• These are ester of fatty acids with various alcohols e.g
glycerol in neutral fats and cytyl alcohol in waxes.
• a. Neutral fat or triglycerides
• These are formed by esterification of three molecule of
fatty acid with one molecules of trihydric alcohol,
glycerol.
• If two number of fatty acids attached to a glycerol, the
ester is called diglyceride, or monoglyceride if there is
only one molecules of fatty acid attached to a glycerol
molecules.
• Animal triglycerides contain a higher proportion
of long chained saturated fatty acids such as
palmitic and stearic acid, resulting higher
melting points.
• Thus at room temp, they are semisolid or solid .
• Most plant triglyceride contain a larger
proportion of short chained unsaturated fatty
acids like oleic, linoleic or linolenic acids.
• They have low melting points and are liquids at
room temp.

B. Waxes

• They are fatty acid esters of long chain
monohydric alcohols like cytyl, ceryl or mericyl.
• Waxes are chemically immobile as they do not
have double bonds in their hydrocarbon chains
and are highly insoluble in water.
• Plant waxes occur in cuticle on the leaf surface.
• In animal, cutaneous gland are known to secrete
wax lanolin for forming a protective water soluble
coating on animal hair.
• Bees wax is formed from palmitic acid C16H32O2,
and mericyl alcohol C30H61OH or ear wax is
secreted by coetaneous gland for lubricating ear
drum.

• C. Cutin

• It is complex lipid produced by cross esterification and
polymerisation of hydroxy fatty acid as well as other
fatty acids or without esterification by alcohol other
than glycerol.
• Cutin occurs in the aerial epidermal cell walls a wells as
a separate layer of cuticle on the outside of these
epidermal cells.
• Cuticle has 50-90% cutin.

• D. Suberin

• It is a mixture of fatty material having condensation
products of glycerol and phenolic acid or its derivatives.
• It occurs in the walls of cork cells and endodermal cell
making the cell wall strong and impregnable.

2. Compound lipids

• These are esters of fatty acids and alcohol with
additional compounds such as phosphoric acid,
sugars, proteins ect.
• These are classified
• Phospholipids
• They are triglyceride lipid where one fatty acid is
replaced by phosphoric acid which is often linked to
additional nitrogenous group like choline in lecithin,
ethanolamine in cephalin, serine or inositol.
• Phospholipids carry both hydrophobic nonpolar and
hydrophilic polar groups.
• In sphingophospholipid the phospholipid
contain amino alcohol sphingosine.
• Sphingomyelins contain an additional
phosphate attached to choline.
• In sphingomyelin, amino group of the
sphingosine backbone is linked to a fatty acid
by an amide bond.
• On hydrolysis, sphingomyelins yield fatty acid,
phosphoric acid, choline and a complex amino
alcohol sphingosine.
• They are found in large quantities in brain and
nerve tissue, especially in the myelin sheath of
the nerves

• Glycolipids

• They are sugar containing lipid and consist of high
molecular weight fatty acid, sphingosine and sugar
residue galactose.
• They occur in nerve membrane, adrenals, kidney,
leucocytes and retina.
• Individual cerebrosides are differentiated by the
type of fatty acids in the molecule such as kerasin
containing the saturated lignoceric acid, cerebron
containing the cerebronic acid, nervon containing
the nervonic acid.

• • 4. Hydrocarbons

• These are substances which do not have any
structural relation to fatty acids but yet are grouped
with lipid only because of their similar solubility
properties.
• They include carotenoids, vit-A, E, K
• Carotenoids is related to lipid. They are fatty acid
like carbon chain carrying carbon at each end.
• They have general formula C40H56 .
• These compound serve as pigment in both plant
and animal matter.
• These are two classes of carotenoids viz., carotenes,
xanthophylls.
• These contain N acetylneuraminic acid, fatty acids,
sphingosine and three molecules of hexose (glucose
and galactose.
• Gangliosides occur in grey matter.

• Lipoproteins
• Protein molecules conjugated with triglycerides, 

cholesterol or phospholipids are called lipoprotein.
• Two important groups of lipoprotein are low density
lipoprotein and high density lipoprotein.
• It present in blood, milk and egg yolk.

3. Steroids

• The steroid are generally considered along with
lipid, although they differ from them in
chemical structure.
• All steroids have in common the basic ring
structure which possess 17-carbon nucleus of
four fused hydrocarbon ring , cyclopentano
perhydro phenenthrene.
• The steroid include such as substance as
cholesterol and other sterols, the sex hormones
and the hormones of the adrenal cortex.

• Sterols

• Steroid with 8-10 carbon atom in side chain at
position 17 and an alcoholic hydroxyl group at
position 3 are classed as sterols e.g cholesterol,
stigmasterol, campesterol, sitosterol, ergosterol.
• Cholesteol is the common sterol found in many
animals, human being and some plants.
• It occurs in both free and combined form when it is
esterified with fatty acid.
• It is precursor of steroid hormone like
progesterone, estradiol, testosterone, aldosterone,
cortisol, ecdysone.

• 4. Hydrocarbons

• These are substances which do not have any
structural relation to fatty acids but yet are grouped
with lipid only because of their similar solubility
properties.
• They include carotenoids, vit-A, E, K
• Carotenoids is related to lipid. They are fatty acid
like carbon chain carrying carbon at each end.
• They have general formula C40H56 .
• These compound serve as pigment in both plant
and animal matter.
• These are two classes of carotenoids viz., carotenes,
xanthophylls.