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
Date – 05/12/2020 Practical number – 05 Title – Qualitative analysis of carbohydrates. Objective - To be familiarized with how to perform different chemical tests and classify different carbohydrate materials. •Introduction – Carbohydrates 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.
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 -
•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
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