#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:
·
Micro molecules
·
Carbohydrates
·
Monosaccharide
·
Oligosaccharides
·
Disaccharides
Micro molecules in cell
Carbohydrates
Carbohydrates are the
most abundant organic molecules in nature. They are produced during
photosynthesis of autotrophic plants.
Carbohydrates are
hydrates of carbon. They are compounds containing carbon hydrogen and oxygen
which generally occur in the ratio of 1:2 :1. A general formula for the
carbohydrates is CnH2nOn.
Carbohydrates can be
aldoses or ketoses depending upon whether they have an aldehyde or Ketone
group. Chemically
the carbohydrates are defined as polyhydroxy aldehydes and ketones. In
these molecules the carbon atom forms chains or rings with two or more hydroxyl
groups and either an aldehyde or Ketone group. They
are also called saccharides as their
basic component is sugar.
Classification of carbohydrates
Carbohydrates are
broadly classified into three groups monosaccharides, oligosaccharides and
polysaccharides. This categorisation is based on the number of sugar units.
Monosaccharides
The monosaccharides are
the simplest carbohydrates. They cannot be hydrolysed into smaller units. On
the basis of number of carbon atoms the monosaccharides are of different types.
(Trioses, tetroses, pentoses, hexoses, heptoses)
Hexoses
Glucose is the most
common and most important monosaccharide in living systems. It is
commonly called grape sugar corn sugar. It is called dextrose being
dextrorotatory. It is the blood sugar and common respiratory substrate.
Fructose is the most common sugar in fruits. It is commonly called fruit
sugar. It also occurs in nectar and honey. It is the sweetest among the
natural sugars. It is called levulose because of its laevo rotatory
nature. Galactose is called brain sugar.
(many simple sugars rotate
the polarised light to the right or left. These are respectively called
dextrorotatory and levorotatory)
Monosaccharides are
linked by glycosidic Bond (C-O-C) form oligosaccharide or polysaccharide. The
process involves loss of water and is called condensation. It is also
called dehydration as it loses water.
Functions
·
Glucose is the main respiratory substrate
· Trioses, glyceraldehyde and dihydroxyacetone are intermediates of
both respiratory and photosynthetic Pathways.
·
Arabinose and xylose( pentoses)are components of hemicellulose.
· Ribose is a component of RNA and ATP. Deoxyribose occurs in DNA.
Oligosccharides
Oligosaccharides are
small carbohydrates which are formed by condensation of 2-9 monosaccharides. The
oligosaccharides are classified according to the number of their monosaccharide
units. There are disaccharides, trisaccharides, tetrasaccharides,
pentasaccharides, etc.
The smallest and commonest oligosaccharides are disaccharides.
Disaccharides
Disaccharide are
condensation products of two monosaccharide units. In disaccharide,
monosaccharide units are held Together by a glycosidic bond. It is normally
formed between carbon atoms 1 and 4 of the neighbouring units( Alpha 1 -4 Bond)
. The monosaccharide units when linked up are called residues.
Examples of disaccharides
Sucrose
It is the common table
sugar also called Cane sugar because most of it is obtained from sugarcane
(saccharum officinarum). Sucrose is formed by condensation of one molecule each
of glucose and fructose. Glycosidic bond is established between carbon
atom 1 of glucose and carbon atom 2 of fructose (Alpha 1, 2 linkage) and a
molecule of water is released. Sucrose is a non reducing sugar.
Maltose
Maltose or malt
sugar is a reducing sugar which is formed by condensation of two molecules of
glucose . Glycosidic bond is formed between carbon 1 of first glucose molecule
and carbon 4 of second glucose molecule (Alpha 1,4 linkage). It is found
in malted grains in Barli, germinating seeds and tissues where starch is broken
down.
Lactose
Lactose or milk sugar is
a reducing sugar which is formed inside mammary glands by beta 1,4 condensation
of two hexose molecules glucose and galactose.
Differences between reducing and nonreducing sugars
Reducing sugars
The Sugars have a free
aldehyde (-CHO) or Ketone (-CO) group.
The Sugars can reduce
cupric ions (Cu2+) of Benedict for Fehling's solution to cuprous ions (Cu+)
during which the blue colour of copper sulphate changes to brick red.
Non reducing sugars
A free aldehyde or
ketone group is absent.
Do not reduce cupric
ions to cuprous ions.
Trehalose
A disaccharide called
trehalose is the major sugar of insect haemolymph. It is also found in
fungi.
Functions
·
Sucrose serves as reserve food for sugarcane and sugar beet.
·
The oligosaccharides attached to the cell membrane help in
recognising cells of their own kind or species.
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