Carbohydrates And Monosaccharide Notes No# 1

full notes on carbohydrates and monosaccharide general aspects.
Carbohydrates, or carbs, are sugar molecules. Along with proteins and fats, carbohydrates are one of three main nutrients found in foods and drinks. Your body breaks down carbohydrates into glucose. Glucose, or blood sugar, is the main source of energy for your body's cells, tissues, and organ.
organic macromolecules that are made up of carbon, hydrogen, and oxygen atoms and are used for energy storage or as structural molecules.

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2. Notes on carbohydrates and monosaccharides

3. carbohydrates General Aspects

4. I ntroduction Carbohydrates are aldehydes or ketone compounds with multiple hydroxyl groups. It is found in relatively in all animals and plants. They are the most abundant biomolecule on earth. But in human they form only 1%of body mass.

5. H istory of carbohydrate Word carbohydrate is derived from the fact that the first compound of carbohydrate had an empirical formula C1H2O1. This formula was showing hydrogen and oxygen in same ratio as in water 2:1. But now it is known that many carbohydrate hydrogen and oxygen not in same proportion as in water. E.g. Deoxyribose whose molecular formula is C5H10O4.

6. Meaning of carbohydrate Carbohydrate is derived from two words Carbo which means Carbon and Hydrate which means Water. So simply it signifies hydrate of water.

7. Definition of carbohydrate Carbohydrate is define as “the polyhydroxylated compound with at least three carbon atom with potentially active carbonyl group. This carbonyl group may be aldehyde or ketone. Carbohydrate contain carbon , hydrogen and water. But some also contain nitrogen , phosphorus, or sulfur.

8. Meaning of saccharide Carbohydrate including sugar are called saccharide. “Saccharides "is from Greek word saccharon which means sugar.

9. Functions of Carbohydrates Carbohydrates have a wide range of functions. The following of them are: Source of energy for living beings, e.g. glucose Storage form of energy, e.g. glycogen in animal tissue and starch in plants Carbohydrates serve as structural component, e.g. glycosaminoglycan's in humans , C ellulose in plants and chitin in insects Non-digestible carbohydrates like cellulose, serve as dietary fibers.

10. Constituent of nucleic acids RNA and DNA, e.g. ribose and deoxyribose sugar. Play a role in lubrication, cellular intercommunication and immunity. Carbohydrates are also involved in detoxification, e.g . glucuronic acid.

11. Classification of carbohydrate Carbohydrate are divided into following classes Monosaccharide Disaccharide Oligosaccharide Polysaccharide Derived carbohydrate Lets explain them one by one

12. Monosaccharide These include simple sugar which consist of a single polyhydroxylated aldehyde or ketone units. They cannot be further hydrolyzed into simple carbohydrate as they are the simplest form of the carbohydrate. with few exception it has the empirical formula (CH2O)n where n=3 or larger number

13. When aldehyde is present in monosaccharide then it always occur at the end of carbon chain. But when ketone is present then it never occur at the end but at some other place. For example glucose contain aldehyde while fructose contain ketone group. The most abundant monosaccharide in nature is six carbon sugar D-glucose.

14. Subdivision of monosaccharide M ay be subdivided into two groups as follows: Depending upon the number of carbon atom they posses For example ;trioses, tortoises , pentose's , hexoses , heptodes. Depending upon the functional aldehyde (CHO) or ketone (C=O ) group present: Aldoses and ketoses

15. Classification of monosaccharide Classification of monosaccharide's based on the number of carbon and the type of functional group present examples are given in table;

16. Biologically important monosaccharide It is given in the table;

17. Isomerism in monosaccharide The compounds possessing identical molecular formula but different structures are referred to as isomers . The phenomenon of existence of isomers is called isomerism. (Greek “isos” means equal, “meros” means parts).

18. The five types of isomerism exhibited by sugar are as follows: 1 . Ketose-aldose isomerism 2. D and L isomerism 3. Optical isomerism 4. Epimerism 5. Anomerism

19. ketose-aldose isomerism Glucose and fructose are isomers of each other having the same chemical (molecular) formula C6H12O6 . B ut they differ in structural formula with respect to their functional groups. There is a keto group in position two of fructose and an aldehyde group in position one of glucose. This type of isomerism is known as ketose-aldose isomerism.

20. D and L Isomerism D and L isomerism depends on the orientation of the H and OH groups around the asymmetric carbon atom adjacent to the terminal primary alcohol carbon , e.g. carbon atom number 5 in glucose determines whether the sugar belongs to D or L isomer . D stand for dextrorotatory designated as (+) L stand for levorotatory designated as (-)

21. When OH group on this carbon atom is on the right, it belongs to D-series, when it is on the left; it is the member of the L-series . The structures of D and L-glucose based on the reference monosaccharide, D and L glyceraldehyde, a three carbon sugar. • D and L isomers are mirror images of each other. These two forms are called enantiomers.

22. Enantiomers These are the pair of stereoisomer that are the mirror image of each other in regard to asymmetric carbon atom present in the molecule. For example D and L form of glucose isomer. The D and L monosaccharide are metabolized by a specific enzymes. The D enzymes will not work on L enzymes and vice versa. In mammals mostly D-type of monosaccharide are present.

23. Optical isomerism The presence of asymmetric carbon atoms exhibits optical activity on the compound. Optical activity is the capacity of a substance to rotate the plane polarized light passing through it. When a beam of plane-polarized light is passed through a solution of an optical isomer, it will be rotated either to the right and is said to be dextrorotatory (d) or (+) or to the left and is said to be, levorotatory (l) or (-). • When equal amount of D and L isomers are present, the resulting mixture has no optical activity. Since the activity of each isomer cancel one another, such a mixture is said to be a racemic or dl mixture

24. Naturally occurring glucose is dextro while fructose is levorotatory. Optical activity in monosaccharide: Light being an electromagnetic radiation vibrates in plane which are perpendicular to its direction od propagation. If light is made to pass through a certain media then the light leaving these media possess only one plane of oscillation. In other words light becomes polarized in one plane and such a light is called plane-polarized light.

25. Plane-polarized light is measured in a Polari meter or Polaris cope. Principle of instrument: A beam of light of known wave length is passed through a nicol prism. This prism is acting as the polarizer converts it into a plane polarized light. This beam is then passes through a solution of a chemical substance contained in a glass tube of known length. A 2 nd nicol prism acts as analyzer it can be rotated to find out degree of rotation.

26. Epimerism When two monosaccharide's differ from each other in their configuration around a single asymmetric carbon (other than anomeric carbon) atom, they are referred to as epimers of each other. For example, galactose and mannose are two epimers of glucose. They differ from glucose in the configuration of groups (H and OH) around C-4 and C-2 respectively. Galactose and mannose are not epimers of each other as they differ in configuration at two asymmetric carbon atoms around C-2 and C-4.

27. Anomerism α and β Anomerism: The predominant form of glucose and fructose in a solution are not an open chain. Rather, the open chain form of this sugar in solution cyclize into rings. An additional asymmetric center is created when glucose cyclizes. Carbon-1 of glucose in the open chain form becomes an asymmetric carbon in the ring form and two ring structures can be formed . These are : • a-D-glucose • b-D-glucose The designation a means that the hydroxyl group attached to C-1 is below the plane of the ring, b means that it is above the plane of the ring. The C-1 carbon is called the anomeric carbon atom and so, a and b forms are anomers.

28. CHEMICAL PROPERTIES OF MONOSACCHARIDES Some of the important chemical properties of monosaccharide's are : 1. Action of strong acids: Furfural formation 2. Action of alkalis: Enolization 3. Oxidation: Sugar acid formation 4. Reduction: Sugar alcohol formation 5. Action of phenyl hydrazine: Osazone formation.

29. 1.Action of Strong Acids (Furfural Formation) On heating a sugar with mineral acids (H2SO4 or HCl), the sugar loses water and forms furfural derivatives . These may condense with a-naphthol, thymol, or resorcinol to produce colored complexes. This is the basis of the: • Molisch’s test • Seliwanoff’s test • Bial’s test • Tollen’s-phloroglucinol-HCl test.

30. 2.Action of Alkalis (Enolization) On treatment with dilute aqueous alkalis, both aldoses and ketoses are changed to enediols . Enediol is the enol form of sugar because two OH groups are attached to the double bonded carbon . • Enediols are good reducing agents and form basis of the Benedict’s test and Fehling’s test . • Thus, alkali enolizes the sugar and thereby causes them to be strong reducing agents. • Through the formation of a common 1, 2-enediol, glucose , fructose, and mannose may isomerize into each other in a dilute alkaline solution

31. 3.Oxidation (Sugar Acid Formation) When aldoses oxidize under proper conditions they may form: –– Aldonic acid –– Saccharic acids –– Uronic acid. • Oxidation of an aldose with hypobromous acid (HOBr ), which acts as an oxidizing agent gives aldonic acid. Thus, glucose is oxidized to gluconic acid. • Oxidation of aldoses with nitric acid under proper conditions converts both aldehyde and terminal primary alcohol groups to carboxyl groups, forming saccharic acid .

32. 4.Reduction to Form Sugar Alcohol Both aldoses and ketoses may be reduced by enzymes or non-enzymatically to the corresponding polyhydroxy alcohols. Manitol, the sugar alcohol derived from mannose, is frequently used medically as an osmotic diuretic to reduce cerebral edema. • Sorbitol, the sugar alcohol derived from glucose, often accumulates in the lenses of diabetics and produces cataracts .

33. 5. Action of Phenyl hydrazine (Osazone Formation) Osazones are yellow or orange crystalline derivatives of reducing sugars with phenylhydrazine and have a characteristic crystal structure, which can be used for identification and characterization of different sugars having closely similar properties (like maltose and lactose). Osazone formed from glucose, mannose, and fructose are identical because these are identical in the lower four carbon atoms. The osazone crystals of glucose and of the reducing disaccharides , lactose and maltose differ in forms –– Glucosazone is needle shaped –– Lactosazone is powder puff or tennis ball shaped –– Maltosazone is sunflower shaped . Non-reducing sugars like the disaccharide sucrose cannot form osazone due to the absence of a free carbonyl (CHO or C = O) group in them.

34. DERIVATIVES OF MONOSACCHARIDES Some important sugar derivatives of monosaccharide's are: • Phosphoric acid ester of monosaccharide's • Amino sugar • Deoxy sugars • Sugar acids • Sugar alcohols • Neuraminic acid • Sialic acid.

35. Importance of Phosphoric Acid Ester of Monosaccharide's Phosphorylation of sugar within cells is essential to prevent the diffusion of the sugar out of the cell. • Nucleic acids (RNA and DNA) of cell nuclei also contain sugar phosphates of ribose and deoxyribose.

36. Importance of Amino Sugar • Amino sugars are components of glycolipid (ganglioside ), glycoprotein , and proteoglycans (glycosaminoglycan's). • Several antibiotics, e.g. erythromycin, carbomycin contain amino sugar.

37. Deoxy Sugars Deoxy sugars possess a hydrogen atom in place of one of their hydroxy groups e.g. 2-deoxyribose found in nucleic acid DNA.

38. Sugar Acids Sugar acids are produced by oxidation of the monosaccharide's, for example: • Ascorbic acid or vitamin C (not synthesized by human beings) is required for the synthesis of collagen. It acts as water soluble antioxidant. • Glucuronic acid (uronic acid) ( see properties of monosaccharide: oxidation ).

39. Neuraminic Acid Neuraminic acid is a nine carbon sugar derived from mannosamine (an epimer of glucosamine) and pyruvate. Mannosamine + Pyruvate ————> Neuraminic acid

40. Importance of sialic acid Sialic acids are constituents of both glycoproteins and glycolipids (ganglioside ).