#biostripsmedia# #pratheeshpallath#
In this session Bio Strips Media takes through the important
topics of Biomolecules. It is one of the most important and scoring topics in
Plus One Biology Exam and NEET Exam.
This lecture covers:
·
Lipids
·
Simple lipids
·
Neutral fats
·
Glycerol
·
Fatty acids
·
Oils
·
Waxes
·
Compound lipids
·
Phospholipids
·
Glyco lipids
·
Lipoproteins
·
Derived lipids
·
Steroids
·
Cholesterol
·
Prostaglandins
·
Terpenes
The content being discussed in this video will be helpful for those
appearing for the Plus One Biology Exam and NEET Biology Exam.
The information in this video is very useful to them and it helps
those NEET aspirants to score maximum marks in Biology.
The Biology content in this video will be helpful for those
candidates appearing for Kerala SET Zoology Exam, Kerala SET Botany Exam, KTET
Natural Science Exam and various other Entrance Exams.
Lipids
Lipids are fatty acid esters of alcohols and related substances. Which are insoluble in water but get dissolved in a number of non polar organic solvents like ether, benzene, chloroform, acetone , etc. however they can form colloidal Complex and get dispersed uniformly in water in the form of minute droplets. The complex is called emulsion.
Lipids consists of a
polar or hydrophilic (attracted to water) head and 1 to 3 nonpolar or
hydrophobic (repelled by water) tales. Since lipid have Both functions they are
called amphipathic.
Classification of lipids
Lipids may be broadly
classified into simple, Complex and derived lipids.
Simple lipids
These are esters of
fatty acids with alcohols. They are of two types:
Ester - organic acids and alcohol react to form esters just as
inorganic acids and bases react to form salts.
Neutral or true fats - These are esters of
fatty acids with glycerol. They are also called glycerides.
Neutral fats are
composed of carbon, hydrogen and oxygen but have far fewer oxygen atoms than
carbon atoms.
A fat molecule consists
of two components. One molecule of alcohol called glycerol and one to three
molecules of the same or different long chain fatty acids.
Glycerol
A glycerol molecule has
three carbons, each bearing a hydroxyl group.
Fatty acids
A fatty acid molecule is
an unbranched chain of carbon atoms with each carbon atom forming for bonds to
other atoms. It has a carboxyl group -COOH at one end and hydrogen atom bonded
to all or most carbon atoms forming a hydrocarbon chain. The
carboxyl group gives the molecule its acidic properties. Most fatty acids have
an even number of carbon atoms between 14 and 22 , mostly 16 or 18.
Fatty acids are of two
types saturated and unsaturated:
Saturated fatty acids
In saturated fatty
acids all carbon atoms are linked by single bonds and each carbon atom carries
a hydrogen atom. They cannot take up any more hydrogen hence saturated.
The saturated fatty acids are straight chains.
They have higher melting point than unsaturated fatty
acids and are solid at ordinary temperature. They
have a general formula of CnH2nO2.
Eg. palmitic acid [C16H32O2]
and stearic acid [C18H36O2].
Most animal fats have
saturated fatty acid.
Unsaturated fatty acids
In unsaturated fatty
acids two adjacent carbon atoms at one or more places lack Hydrogen atoms and
are interlinked by double bonds (C=C).They can take up additional hydrogen
hence unsaturated.
Their general formula is
CnH2n-2xO2. They have lower melting point and a liquid at normal
temperature. Most plant lipids have
unsaturated fatty acids. These include 18
carbon Oleic,(C18H34O2) linoleic,(C18H32O2) and linolenic acids(C18H30O2) and
20 carbon arachidonic acid. (C20H32O2).
Formation of fats
The three hydroxyl
groups of glycerol molecule join with the carboxyl group of 3 fatty acid
molecules to form a fat or glyceride molecule. The chemical linkage between the
glycerol and fatty acids is called the Ester Bond. Inter results from the elimination of three molecules of
water( condensation or dehydration).
Pure fats
Fats with three similar
fatty acids .Example: tripalmitin, tristearin.
Mixed fats
Fats having different
fatty acids. Example: butter, dipalmito-stearin.
Oils
Fats which are liquid at
room temperature.They are rich in unsaturated fatty acids, have low melting
point and forms hard fats on hydrogenation. Example:groundnut oil ,mustard oil,
olive oil, etc.
Hard fats
Fats solid at room
temperature of about 20 degree Celsius they contain long chain saturated fatty
acids. Eg. animal fat, butter, etc.
Types of fats
A true fat having three
molecules of fatty acid is called triglyceride. A fat having only one or two
fatty acid molecules is termed monoglyceride or diglyceride.
Waxes
The waxes are lipids
which are composed of long chain saturated fatty acids and a long chain
saturated alcohol of high molecular weight instead of glycerol.
Example:
Bees wax- It is a secretion of the abdominal glands of
worker honey bees. It is a thick tenacious material plastic at room temperature.
Sebum - it is a fatty secretion of the sebaceous glands of the skin.
Cerumen - it is a soft brownish waxy secretion of the ceruminous glands
of the external auditory Canal. It is commonly called ear wax.
Paraffin wax- a translucent waxy substance obtained from Petroleum.
Compound lipids or conjugated lipids
These are esters of fatty
acids with alcohol but contain some other substances also.
Phospholipids
These are composed of a
molecule of glycerol or other alcohol having a phosphate group joined to one of
its outer OH groups, two fatty acid molecules linked to the other two OH groups
and a nitrogen containing base bound to the phosphate group.
A phospholipid molecule
has a strongly non-polar hydrophobic tail consisting of fatty acid chains and
polar hydrophilic head comprising a negatively charged phosphate group and a
positively charged base.
The phospholipids form
the framework of the cell, nuclear, mitochondria, chloroplast and endoplasmic
reticulum membranes.
Some phospholipids like
lecithins are constituent of cytoplasm and some occur in storage fats.
Certain phospholipids, spingo myelins insulate the nerve fibres.
Lipoproteins
Lipoproteins contain
lipids (mainly phospholipids) and proteins in their molecules.
They are main
constituent of membranes. Lipoproteins occur in the milk and egg yolk. Lipids
are transported in the blood plasma and lymph as lipoproteins. They are the
transport vehicles for lipids in the circulation.
Glycolipids
Glycolipids contain
fatty acids, alcohol and sugar (galactose) the later replaces 1 fatty acid
molecules.
Cutin and suberin
Cutin is found in
the plant cell walls and cuticle.
It binds epidermal cells and reduces transpiration.
Suberin is present in the walls of cork cells. It makes cell wall strong and impermeable to water.
Derived lipids
These are the
derivatives obtained on the hydrolysis of simple and compound lipids.
Eg. Steroids, Terpenes
and Prostaglandins
Steroids
Steroids are the
compounds containing a cyclic steroid nucleus or ring namely cyclopentanoperhydro
phenanthrene (CPPP). The steroids do not contain fatty acids but are included
in the lipids because they have fat like properties. They are not straight
chain compounds rather they are composed of four fused Carbon rings.
Major groups of Steroids
Sterols:
Eg. cholesterol,
ergosterol
Bile acids:
Eg. Glycocholic acid
taurocholic acid
Gonadal( sex )hormones:
Oestrogen, progesterone,
testosterone
Adreno cortical hormones:
Aldosterone and
cortisone
Cholesterol
It is the most abundant
steroid in the animal tissues . It is present in food especially that is rich
in animal fats. It is also formed in the liver itself. Its formula is C27H45OH. The cholesterol and its
esters are insoluble in water. Therefore they
are deposited on the lining of the blood vessels leads to high blood pressure
and many heart diseases. Cholesterol forms
vitamin D on exposure to ultraviolet rays.
Terpenes
They are lipids like
hydrocarbons formed of isoprene [C5H8] units. Terpenes
are a major component of essential oils produced by certain plants. They impart fragrance to plant parts.
Eg. Camphor, menthol,
limonene, phytol, carotenoids, lycopene, gibberlins,etc
Prostaglandins
The prostaglandins are
hormone like compounds derived from 20 carbon polyunsaturated fatty acids such
as arachidonic acid. Their richest sources are the secretion of seminal vesicles
in males and menstrual secretion fluid in the females. The prostaglandins have a variety of effects such as vasodilation,
vasoconstriction , stimulation of intestinal smooth muscles, etc.
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