2. LIPIDS
•Lipids are organic compounds that contain hydrogen, carbon, and oxygen
atoms, which forms the framework for the structure and function of living
cells.
• The lipids are a large and diverse group of naturally occurring organic
compounds that are related by their solubility in nonpolar organic solvents
(e.g. ether, chloroform, acetone & benzene) and general insolubility in water.
•Lipids are relatively simple molecules responsible for a variety of functions in
our body, including energy storage and transmitting signals.
•Lipids are everywhere in your body- from hormones, cellular structures, and
more, these molecules can be synthesized in the liver.
4. LIPIDS CLASSES
Lipids can be classified into two main classes:
1. Nonsaponifiable Lipids: A nonsaponifiable lipid cannot be
disintegrated into smaller molecules through hydrolysis.
Nonsaponifiable lipids include cholesterol, prostaglandins, etc.
2. Saponifiable Lipids: A saponifiable lipid comprises one or more ester
groups, enabling it to undergo hydrolysis in the presence of a base,
acid, or enzymes, including waxes, triglycerides, sphingolipids and
phospholipids.
5. LIPIDS CLASSES
Further, these categories can be divided into non-polar and polar
lipids:-
•Nonpolar lipids, namely triglycerides, are utilized as fuel and to store
energy.
•Polar lipids, that could form a
barrier with an external water
environment, are utilized in membr
-anes. Polar lipids comprise Sphingo
lipids and glycerophospholipids.
6. FAHS | PALLAVI BASRA
LIPIDS COMPOSITION
•They are made from two molecules:
i. Fatty Acids
ii. Glycerol
•A Glycerol molecule is made up
from three Carbon atoms with a
Hydroxyl Group attached to it and
Hydrogen atoms occupying the
remaining positions.
FATTY ACID
GLYCEROL
7. BIOLOGICAL FUNCTIONS
•Their varied biological functions include energy source, energy
storage, cell membrane structural components, hormones, vitamins,
vitamin adsorption, protection, and insulation.
•The spectrum of lipid functions can be condensed into the three broad
areas of:
1. Storage of energy.
2. Structure of cell membranes.
3. Signal of chemical biological activities.
10. 1. FATTY ACIDS (SATURATED AND UNSATURATED).
2. GLYCERIDES (NEUTRAL GLYCERIDES AND PHOSPHO
GLYCERIDES).
3. NONGLYCERIDE (SPHINGOLIPIDS , STEROIDS , WAXES).
4. COMPLEX LIPIDS (LIPO PROTEINS).
CLASSIFICATION OF LIPIDS
11. 1. FATTY ACIDS
•Fatty acids consist of an Acid Group at one end of the molecule
and a Hydrocarbon Chain, which is usually denoted by the letter
‘R’.
•Lipids are the polymers of fatty acids that contain a long, non-
polar hydrocarbon chain with a small polar region containing
oxygen.
•Fatty acids are carboxylic acids (or organic acid), usually with
long aliphatic tails (long chains), either unsaturated or saturated.
13. i. SATURATED FATTY ACIDS
•Lack of carbon-carbon double bonds indicate that the fatty
acid is saturated.
•The saturated fatty acids have higher melting points
compared to unsaturated acids of the corresponding size due
to their ability to pack their molecules together thus leading to
a straight rod-like shape.
•A fatty acid is saturated if every possible bond is made with a
Hydrogen atom, such that there exist no C=C bonds.
14. i. SATURATED FATTY ACIDS
•Animals tend to have more saturated, and
consequently solid at room temperature lipids
and they tend to get tightly packed.
15. i. SATURATED FATTY ACIDS
•Saturated fats contribute to plaque formation in the arteries,
which increases the risk of a heart attack.
•Animal fats with stearic acid and palmitic acid contained in
meat, and the fat with butyric acid contained in butter, are
examples of saturated fats.
•Mammals store fats in specialized cells called adipocytes, where
globules of fat occupy most of the cell.
•In plants, fat or oil is stored in seeds and is used as a source of
energy during embryonic development.
16. ii. UNSATURATED FATTY ACIDS
•Unsaturated fatty acids contain C=C bonds.
•Monounsaturated fatty acids have one C=C bond and
polyunsaturated have more than one C=C bond.
•Unsaturated fatty acids contain a cis-double bond(s) which create
a structural kink that disables them to group their molecules in
straight rod-like shape.
•Plants tend to have more unsaturated and so fluid at room
temperature lipids that prevents the fatty acids from packing
tightly.
17. ii. UNSATURATED FATTY ACIDS
•Olive oil, corn oil, canola oil, and cod liver
oil are examples of unsaturated fats.
•Unsaturated fats help to improve blood
cholesterol levels.
18. 2. GLYCERIDES
• Glycerides are lipid esters of the glycerol molecule and fatty acids.
• Any of the esters formed from glycerol reacting with fatty acids, and
function primarily as fat storage molecules.
• Glycerides can be subdivided into two categories:
i. The first group, the neutral glycerides are nonionic and nonpolar.
Esterification of glycerol with a fatty acid produces a neutral
glyceride. Esterification may occur at one, two or all three positions
producing monoglycerides (monoacylglycerols), diglycerides
(diacylglycerols), or triglycerides (triacylglycerols). The most prevalent
and most important are the triglycerides.
20. 2. GLYCERIDES
ii. The second group, the phosphoglycerides contain a polar region,
the phosphoryl group. They are also among the primary building
blocks of all cellular membranes. Vital organs such as the liver and
reproductive tract, and muscles contain high concentration of
phosphoglycerides. Membrane functions include cellular transport
of nutrients and wastes, internal cellular pressure regulation, and
ion exchange.
• Both of these two types of glycerides can be seen as possessing a
three carbon "backbone" of the glycerol molecule.
22. i. SPHINGOLIPIDS
1. Sphingolipids: Sphingolipids are not derived from glycerol,
sphingosine is present instead. They can still be visualized as a
three-carbon backbone molecule just as the triglycerides or the
phospholipids. Instead of the three-carbon backbone of glycerol,
the three-carbon backbone is sphingosine.
Sphingosine is a nitrogen-containing alcohol
(amino alcohol). Sphingolipids contain the
sphingosine backbone, the amide of a fatty acid,
and a polar molecule.
23. SPHINGOLIPIDS TYPES
• The sphingolipids are divided into the two subcategories:
1. The sphingomyelins are the only class of
sphingolipids that are also phospholipids.
2. Glycosphingolipids, or glycolipids, are built
on the backbone structure of ceramide,
which is an amide derivative of sphingosine.
24. ii. STEROIDS
• Stereroids are lipids with the principle function of signaling chemical
biological activities.
• Steroids are members of a large, diverse collection of lipids called the
isoprenoids. All of these compounds are built from one or more five-
carbon units called isoprene.
• They do not contain fatty acids but are included in the lipids because
they have lipid like properties. They are composed of four carbon
rings .
25. ii. STEROIDS
One major class of lipids is the steroids,
which have structures totally different
from the other classes of lipids.
The main feature of steroids is
the ring system of three
cyclohexanes and
one cyclopentane
in a fused ring
system.
26. iii. WAXES
• They are esters of fatty acids with long hydrocarbon chains. The
alcohols in waxes have only one hydroxyl group.
• Cuticle is a waxy coating covering the epidermis of leaves and stem
of plants. It prevents excessive evaporation of water.
• Sebum, the secretion of sebaceous glands in our skin is a mixture of
waxes and triglycerides.
• Due to their high molecular weights, waxes are generally solids at
room temperature.
27. 4. COMPLEX LIPIDS
•Complex lipids are bonded to other types of molecules. Because lipids
are mostly insoluble in water, the movement of lipids from organ to
organ through the bloodstream is facilitated by plasma lipoproteins.
•Lipoprotein provides the surface for biochemical reactions and energy
production and also help in the transportation of lipids and proteins
to the various parts of plant or animal body.
•There are 4 major classes of plasma lipoproteins.
29. INTRODUCTION OF LIPOPROTEINS
•Lipoproteins are special particles made up of droplets of fats
surrounded by a single layer of phospholipid molecules.
•Phospholipids are molecules of fats which are attached to a
phosphorus-containing group. They are distinctive in being
amphipathic, which means they have both polar and non-polar
ends.
•In a lipoprotein, the polar ends of all the phospholipid molecules face
outwards, so as to interact with water, itself a polar molecule. This
enables the lipoprotein to be carried in the blood rather than rising to
the top, like cream on milk.
30. INTRODUCTION OF LIPOPROTEINS
•The non-polar fat balled up inside
the phospholipid layer, at the
center of the lipoprotein, is thus
transported to the place where it
must be stored or metabolized,
through the bloodstream, despite
being insoluble in blood. Thus
lipoproteins are molecular level
trucks to carry fats wherever they
are required or stored.
31. TYPES OF LIPOPROTEINS
1. Chylomicrons: These are the largest and least dense of the lipoprotein,
with the highest triglyceride content. They consist of protein component
synthesized in the liver, which wraps around diet-derived cholesterol and
fats.
• It travels from the intestinal lymphatics to the large veins, and sticks to the
inner surface of the tiny capillary blood vessels inside the muscles and the
fat storage cells in various parts of the body.
• There the fat is digested, while the cholesterol remains. This is now called
the chylomicron remnant. It travels to the liver, where the cholesterol is
metabolized. Thus chylomicrons deliver fats and cholesterol from the
intestines to the muscles, fat cells and the liver.
33. TYPES OF LIPOPROTEINS
2. VLDL (very low density lipoprotein): This is composed of protein, fats
and cholesterol synthesized in the liver and carry them to adipose and
other tissues for storage.
• It is associated with 5 different apoproteins, namely , B-100, C-I, C-II,
C-III and E. It is converted to IDL and LDL by removal of the apoprotein
except for one called apoprotein B100, along with esterification of the
cholesterol. They are second only to chylomicrons in the percentage
triglyceride content.
3. IDL (intermediate density lipoprotein): It is created by the metabolism
of VLDL.
35. TYPES OF LIPOPROTEINS
4. LDL (low density lipoprotein): This is the last VLDL remnant, and contains
chiefly cholesterol. The only apoprotein associated with it is apoB-100.
Thus all these forms carry fats and cholesterol produced in the liver to the
tissues.
5. HDL (high density lipoprotein): This has the highest protein: lipid ratio, and
so is the densest. It has the apoprotein A-1. This is also called ‘good
cholesterol’, because it carries cholesterol away from the tissues to the
liver, lowering blood cholesterol levels.
• High HDL levels are associated with lowered risk of cardiovascular disease.
HDL levels are higher with exercise, higher estrogen levels, with alcohol
consumption, and weight loss.
38. DIGESTION AND ABSORPTION
OF LIPIDS
1.Digestion of lipids begins in the mouth as lipids encounter saliva.
Chewing enables the digestive enzymes which initiates process of
digestion.
2.A small amount of lipids digestion occurs in the stomach due to the
gastric lipase produced in the stomach.
3.Bile is produced in the liver, stored in the gall bladder and released into
the small intestine to aid in the digestion and absorption of lipids.
4.The enzyme pancreatic lipase is produced and released into small
intestine to breakdown triglycerides into monoglycerides, fatty acids
and glycerol.
40. DIGESTION AND ABSORPTION
OF LIPIDS
5. In the small intestine, products from fat digestion and bile acids form
a micelle, which moves toward the microvilli to allow the lipids to
diffuse into the mucosal cells.
6. Inside the mucosal cells, the fatty acids and monoglycerides are
resembled into triglycerides and incorporated into lipids. Lipids
transport particles called chylomicrons, which enter the lymph
vessels.
7. The small intestine is very efficient in absorbing fat so very little is
excreted in the feces
