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Qualitative Analysis of Carbohydrates (Assignment)

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Added on  2021-09-30

Qualitative Analysis of Carbohydrates (Assignment)

   Added on 2021-09-30

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BT 12022 – Cell and Biomolecules












Practical number – 05
Qualitative analysis of Carbohydrates
















O.N.M. Perera
196099
Group C2
Qualitative Analysis of Carbohydrates (Assignment)_1

Date 05/12/2020
Practical number05
Title Qualitative analysis of carbohydrates.
Objective - To be familiarized with how to perform different chemical tests and classify different
carbohydrate materials.
IntroductionCarbohydrates are biomolecules. They are mainly consist of Carbon(C),
Hydrogen(H) and Oxygen(O). Normally they have 2:1 ratio of Hydrogen and Oxygen.
Carbohydrates are polymer of monosaccharides. They are the most abundant organic
compound in the living organisms. Carbohydrates are central to nutrition and are found in a
wide variety of natural and processed foods. Carbohydrates are abundant in cereals and
processed food based on cereal flour. In addition, types of carbohydrates such as
polysaccharides can be found in the cell wall of all plants, is one of the main components of
insoluble dietary fiber.
Physical, Chemical and Biological properties of carbohydrates are depend on their primary
structures and less frequently on their high order structures. They have (CH2O)n like empirical
formula. Carbohydrates organized in the form of aldehydes or ketones with multiple hydroxyl
groups coming off the carbon chain.
Carbohydrates provide,
1. Energy and regulation of blood glucose.
2. Sparing the use of proteins for energy.
3. Breakdown of fatty acids and preventing ketosis.
4. Biological recognition processes.
5. Flavor and Sweeteners.
6. Dietary fiber.

There are three main groups of carbohydrates are monosaccharides and polysaccharides. The
simplest carbohydrates are monosaccharides from which disaccharides and polysaccharides are
created. Monosaccharide’s are crystalline solids which are freely soluble in water and insoluble
in nonpolar solvents. There are two types of monosaccharide’s are aldoses and ketoses.
Monosaccharide’s except dihydroxyacetone have asymmetric centres since they contain one or
more asymmetric or chiral carbon atom and hence exist in optically active isomeric forms.
Simple monosaccharide’s are reducing agents and Disaccharides contain a Glycosidic bond.
Usually carbohydrates can be found in nature occur as polysaccharides.
1. Benedict's test: the reduction of sugars when heated in the presence of alkali is converted to a
potent reducing species known as enediols. When the reagent solution of Benedict and the
sugar reduction are heated together the solution changes its color to orange-red/brick red.
Qualitative Analysis of Carbohydrates (Assignment)_2
2. Oxidation: Monosaccharides reduce sugars if their carbonyl groups oxidize to create
carboxylic acids. In Benedict's test, D-glucose is oxidized to D-gluconic acid and thus glucose
is considered to be reducing sugar.
3. Reduction to alcohols: The C=O groups in open-chain forms of carbohydrates can be reduced
to alcohols by sodium borohydride, NaBH4, or catalytic hydrogenation (H2, Ni, EtOH/H2O).
The products are known as “alditols”.


Carbohydrates are divided into 4 groups, They are
1.Monosaccharides
2.Disaccharides.
3.Polysacchaides.
4. Oligosaccharides.

1. Monosaccharides
Monosaccharides are the simplest group of carbohydrates. They cannot be further hydrolyzed.
Therefore, they referred to as simple sugars. They are colorless, crystalline solids that are soluble in
water and insoluble in non-polar solvents. The general formula is Cn(H2O)n and CnH2nOn.
They can be categorized on the basis of the number of carbon atoms they contain and also on the basis
of the functional group present.
Monosaccharides are having 3,4,5,6,7... carbons are respectively called trioses, tetroses, pentoses,
hexoses, heptoses, etc., and even aldoses or ketoses, depending on whether they contain aldehyde or
ketone.
Trioses
It contains three carbon atoms. It has C3H6O3 general formula. There are only two trioses, an aldotriose
(glyceraldehyde) and a ketotriose (dihydroxyacetone). Trioses are important in respiration. Namely,
lactic acid and pyruvic acid are derived from aldotriose and ketotriose, respectively.

Tetroses
Tetrose are containing four carbon atoms. The general formula is C4H8O4
. Example is D- Erythrose-4-P is an intermediate in hexosemonophosphate shunt which is an alternative
of glucose oxidation.

Pentoses
Pentose are containing five carbon atoms. The general formula is C5H10O5.
Examples are -
Qualitative Analysis of Carbohydrates (Assignment)_3
D- ribose is a constituent of RNA and many co-enzymes e.g. FAD, NAD.
D-2 deoxy is a constituent of DNA component of DNA.
D-Lyxose is a constituent of lyxoflavin found in the human heart.
D- arabinose is a constituent of plant cell wall
Phosphate esters of D- Ribulose and D- xylose occurs as an intermediate in the HMP pathway.

Hexoses
Hexoses are containing six carbon atoms. The general formula is C6H12O6.

I. D – Galactose
They are very rarely found to be free in nature as a constituent of milk sugar lactose and in tissues such
as galactolipids and glycoproteins.
II. D – Mannose
D- Mannose used to stamp proteins via the glucosylation process. It can’t be found in free in nature but
is commonly distributed in combination as polysaccharide mannan, e.g. ivory nut. It is also considered
to be a constituent of glycoproteins
III. D- Fructose
it is a ketohexose and is commonly called the fruit sugar, as it occurs in fruit. It is a sweet sugar sweeter
than glucose and sucrose. It is found in honey as laevulose. In the seminal fluid of man fructose is the
chief source of energy for sperms.










2. Disaccharides
Disaccharides are glycosides formed from two monosaccharides that may be aldoses or ketoses. Each
of the—OR groups is given by the original cycle for the hemiacetal or hemiketal distribution. The
second—OR group is derived from an aglycone; it is the second monosaccharide that supplies the
alcohol to the glycosid bond functional group. Maltose, Sucrose, lactose are common disaccharides.

Glucose + Fructose Sucrose
Qualitative Analysis of Carbohydrates (Assignment)_4

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