5. INTRODUCTION:-
The word lipid is derived from a greek word
“lipos” which means FAT.
These are heterogenous group of compounds
Unlike proteins,nucleic
acids,polysaccharides,lipids are not polymers
rather they are small molecules.
They are the chief storage form of
energy,besides their role in cellular structure and
other biochemical functions.
6. DEFINITION:-
Lipids may be regarded as organic substances
relatively insoluble in water, soluble in organic
solvents, actually or potentially related to fatty
acids and utilized by the living cells.
7. FUNCTIONS:-
Fat is stored in adipose tissue, where it also serves
as a thermal insulator in the subcutaneous tissues.
Fatty acid derivatives serve as vitamins(A,D,E&K) or
hormones.
It act as energy/food reservoir (Triacylglycerol).
Several proteins are covalently modified by fatty
acids.
Structural components of biological membranes
(lipoprotein, phospholipids &sphingomyelins) .
8. Lipids act as important cellular metabolic
regulators(PG’s & steroid hormones)
Lipids are compounds in inner mitochondrial
membrane and participate in Electron transport
chain.
9. CLASSIFICATION:-
Lipids are broadly classified into 5 types which
are the following:-
I. Simple lipids
II. Complex lipids
III. Derived lipids
IV. Neutral lipids and
V. Miscellaneous lipids
10. I. SIMPLE LIPIDS:-
Esters of fatty acids with glycerol.
Mainly of two types:-
i. Fats and oils:
-These are esters of fatty acids and glycerol.
-difference b/w fats and oils is physical.
ii. Waxes :
-Esters of fatty acids+alcohol other than
glycerol.
-Cetyl alcohol is most commonly used
11. COMPLEX OR COMPOUND
LIPIDS:-
Esters of fatty acids+Alcohol+other groups like
phosphate,Nitrogenous base,carbohydrate
,Protein,etc.
Based on the group present they are further
classified into:-
i. PHOSPHOLIPIDS:-
• F.A+Alcohol+phosphoric acid as
nitrogenous base.
• Based on the type of alcohol present they
are again divided into
Glycerphospholipids:Contain Glycerol
as alcohol. Eg:lecithin &cephalin
Sphingophospholipids : Contain
sphingosine as alcohol. Eg:
sphingomyelin
12. ii.GLYCOLIPIDS:-
• Fatty acids+alcohol+carbohydrate as
nitrogenous base.
• They contain sphingosine as alcohol and hence
also known as GLYCOSPHINGOLIPIDS.
• Eg: Cerebrosides and Gangliosides.
iii.LIPOPROTEINS:-
• Macromolecular complexes of lipids with
proteins.
• Eg:LDL,VLDL,Chylomicrons,HDL,etc
13. iv. Other complex lipids:-
• Sulfolipids,Aminolipids and other
Lipopolysaccharides come under this.
14. DERIVED LIPIDS:-
These are the derivatives of hydrolysis of simple and
complex lipids which possess the characteristics of
lipids.
These include:
• Lipid soluble vitamins
• Steroid hormones
• Hydrocarbons
• Ketone bodies
• Mono and diacylglycerol ,etc
15. NEUTRAL LIPIDS:-
These are the lipids which are uncharged and
are reffered ro as neutral lipids.
These are mono,di and triacylglycerols,
cholestrol and cholesteryl esters.
16. MISCELLANEOUS LIPIDS:-
A large number of compounds possess
characteristics of lipids,such compounds come
under this category
Example:carotenoids,squalene,hydrocarbons like
pentacosone and terpenes etc.
17. FATTY ACIDS
Carboxylic aicds with hydrocarbon side chains.
Occur in esterified form
They occur in even and odd carbon forms
Saturated and unsaturated.
Essential and non essential fatty acids.
Essential fatty acids are:
Linoleic acid
Linolenic acid
Arachidonic acid.
18. Deficiency of EFA causes phrynoderma or Toad
skin.
Presence of horny eruptions on posterior and
lateral parts of limbs,on the back and buttock,loss
of hair and poor wound healing.
19. TRIACYLGLYCEROLS:-
Esters of fatty acids and glycerol.
Widely distributed
Insoluble in water and non polar hence known as
neutral fats
Serves as fuel reserve sufficient for 2-3 months.
They do not serve as a structural component of cell
membrane.
It is divided again into two types
Simple triacylglycerols
Mixed triacylglycerol
20. TEST TO CHECK FOR PURITY:-
Iodine number
Saponification number
Reichert meissl number(5).
21. PHOSPHOLIPIDS:-
GLYCEROPHOSPHOLIPIDS:-
Phosphatidic acid:- simplest of all,does not
occur in good concentration.
Lecithins:phosphatidic acid +choline as
nitrogenous base.
Storage form of body’s choline
a) Dipalmotyl choline:found in lungs,important
surface active agent preventing adhesion of
inner surface of lungs due to surface tension.
22. b) lysolecithin: formed by removal of fatty acids
from C1 or C2.
Cephalins:
Phosphatidic acid +ethanolamine as nitrogenous base.
Phosphatidyl inositol:
Present in cell membrane.
Cleaves to form inositol phosphate and
diacylglycerol which act as a seconadry
messengers for action of few of the important
hormones like oxytocin,vasopressin etc.
23. PLASMALOGENS:-
Esterification of fatty acid at C1 with glycerol forms
plasmalogens
Present in adequate quantity in brain and muscle
tissue.
CARDIOLIPIN:-
It is structurally two phosphatidic molecules held by
glycerol.
Present in inner mitochondrial membrane and
believed two have function in electron transport
chain.
Possess antigenic properties.
24. SPHINGOMYELINS:-
They contain amino alcohol
It attaches to an amide group by fatty acxid to form
ceramide.
Sphingomyelins are important constituent of brain
and nervous tissue.
25. FUNCTIONS OF PHOSPHOLIPIDS:-
Structural components
Electron transport chain
Absorption of fat
Synthesis of lipoproteins and transport
of fat
Prevents fatty liver
EICOSANOID production
Surfactant
Reverse cholestrol transport
