carbohydrates dr dinesh.pptxcarbohydrates dr dinesh.pptx

carbohydrates dr dinesh.pptxcarbohydrates dr dinesh.pptxcarbohydrates dr dinesh.pptx

1. Chemistry of Carbohydrates

2. What are carbohydrates ? Organic compounds containing the following elements: Carbon Hydrogen Oxygen Normally the ratio of these elements in carbohydrates are: C:H:O is 1:2:1

3. Definition for carbohydrates Carbohydrates may be defined as polyhydroxyaldehydes or ketones or compounds which produce them on hydrolysis. Carbohydrates are containing either aldehyde (-CHO) or keto ( >C=O) group with two or more hydroxyl (-OH) groups. So, carbohydrates are defined as polyhydroxy aldehyde or ketone.

4. Physiological importance of carbohydrates The most abundant organic compounds on earth. The most important source of energy in our body. 60-70% energy requirement of our body is supplied by carbohydrates. Brain & RBC dependent wholly on carbohydrates for their energy requiremen t. It is also an important storage form of energy ( glycogen ) in our body & also in plants ( starch ).

5. Physiological importance of carbohydrates.. It is an important structural component (glycoprotein/glycolipids) of cell wall, receptors and cell organelles Structural component of animals: eg: mucopolysaccharides- lubricants in joints, c hit i n ( e x o s k el e t o n ) of in s e c t s & cell wall of microorganisms It is important for cell growth and adhesion of cells It is an Important structural component of plants, cellulose (cell wall). It is an important dietary fiber required for human beings

6. Carbohydrates: Medical significance Diabetes mellitus Glycogen storage diseases Galactosemia Lactose intolerance

7. Classification of carbohydrates Monosaccharides - simplest sugar D i sa c chari d es - t w o Trisaccharides t h r e e few Oligosaccharides Polysaccharides: - many Homop ol ysaccharides & Heteropolysaccharides

8. Monosaccharide s Simplest sugar Can’t be further hydrolysed into simple sugar Molecular formula: C 6 H 12 O 6 Eg: Glucose Fructose Galactose Mannose

9. Monosaccharides can also be classified on the basis of Number of C - atoms present Number of Carbon atoms Example Structure Triose (C 3 ) Glyceraldehyde Tetrose (C 4 ) Erythrose Pentose (C 5 ) Ribose

10. Monosaccharides can also be classified on the basis of Number of C - atoms present Number of Carbon atoms Example Structure Hexose (C 6 ) Glucose Heptose (C 7 ) Sedoheptulose Nonoses (C 9 ) Neuraminic acid

11. Classification on the basis of : Aldehyde / Keto group Carbohydrates can also be classified into: Aldose sugar : containing aldehyde group Eg: Ri b ose , X yl o s e, G lu c o s e, Mannose & Galactose Ketose sugar : containing keto group Eg: Ribulose, Xylulose, & Fructose

12. Classification: Aldehyde / Keto group Aldo sugar Structure Keto sugar Structure Glyceraldehye Dihydroxy acetone Erythrose Erythrulose Ribose Ribulose Glucose Fructose

13. Disaccharides They are made of two monosaccharides so, on hydrolysis they will give two monosaccharides. Molecular formula: C 12 H 24 O 11 Eg: Sucrose (Glucose + Fructose) Lactose (Glucose + Galactose) Maltose (Glucose + Glucose)

14. Trisaccharides They contain three monosaccharides . On hydrolysis they will give three monosaccharides. Eg: Maltotriose

15. Oligosaccharides They contain 3 to 10 monosaccharides .

16. Monosaccharides Glucose : It is Hexose sugar It is an ‘aldose’ sugar It is a reducing sugar The most important sugar in human beings It is present in blood It is the major source of energy As it is dextrorotatory, it is also known as ‘ Dextrose ’ in clinical practice .

17. Monosaccharides.. Fructose It is also known as ‘fruit sugar’ It is Hexose sugar It is a keto sugar It is a reducing sugar It is a component of sucrose (sugar) It is present in fruits, honey, etc., It is sweeter than sucrose It is present in seminal fluid & important for motility of spermatozoa .

18. Monosaccharides.. Galactose : Gala (Greek)means milk. It is Hexose sugar It is an aldose sugar It is a reducing sugar It is a constituent of lactose (milk Sugar) It is seldom found in free state.

19. Stereoisomer Compou n d s h a vin g sam e molecu l ar f o r m ul a bu t di f f e r from each other in their spatial configuration. P o ss ibl e nu m b e r o f s t e r eo i s o m e r s a r e c a l c u l a t e d on the basis of asymmetric C - atom Formula: 2n . ‘n’ is number of asymmetric c -atoms. Sp a tial a r r a n g e m e n t of - H & - O H in monosaccharides.

20. S t e r e o i s o m er: D & L f o r m s Glyceraldehyde is taken as reference molecule: If –OH is on right - it is D - form If –OH is on left - it is L - form

21. Stereoisomers in carbohydrates In case of monosaccharides, penultimate carbon atom (C5) is the reference carbon atom. In case of glucose, arrangement of -OH on 5 th Carbon Naturally occurring sugars are: D – forms eg : D- Glucose .

22. Optical activity Presence of asymmetric - C makes an organic compound “ Optically active ” – it can rotate plane polarized light towards Right: dextrorotatory left levorotatory (+) / d or (-) / l D- Glucose is dextrorotatory D- Fructose is leavorotatory Equimolar mixture of optical isomers don't have net optical rotation – racemic mixture .

23. E pi m e r s Sugars differ from each other in the spatial arrangement (configuration) of – OH group on a single carbon atom other than penultimate C - atom are known as Epimers Eg: Glucose & Galactose C 4 Glucose & Mannose C 2

24. E pi m e r s Galactose Glucose Ma n n o s e Glucose & Galactose C 4 Glucose & Mannose C 2

25. Epimerisation Conversion of one epimer into another epimer is known as ‘ Epimerisation ’ It occurs in our body, catalysed by the enzyme - ‘ Epimerase ’. Glucose Galactose(liver) E pi meras e

26. Reactions of monosaccharides Enediol formation: Sugars with potential aldehyde / keto group will undergo tautomerisation and forms endediol in mild alkaline medium . G l u c o s e is c o n v er t e d i nt o fruc t o s e & vice v e r s a th r o u gh this intermediate - enediol . This interconversion of sugars through enediol is known as “ Lobry de Bruyn-van Ekenstein ” transformation.

27. Reducing property Sugar with potential (free) aldehyde / keto group has reducing property. Benedict’s test : it is an important test used to detect the presence of reducing sugars. It is commonly used to detect glucose in the urine (glucosuria) sample.

28. Benedict’s test Benedicts reagent contains: Sodium carbonate copper sulphate & sodium citrate. Reducing Sugar forms enediol in alkaline medium and cupric ion (Cu ++ ) into cuprous ion (Cu + ) – it is yellow to red precipitate. r ed u c es It is not specific for glucose Reducing substances like ascorbic acid, homogentisic acid, salicylic acid, glucuronic acid, etc., will also give (false) positive result

29. Osazone formation Reducing sugars react with excess of phenylhydrazine and form osazone crystals of specific structure. Formation of osazone involves 1 st & 2 nd carbons of sugars. Th e di f f e r e n c e in s truc t u r e o f glu c o s e, fruc t o s e and m a nnos e is only in 1 st & 2 nd carbons and this difference is masked during osazone formation. So, Osazone crystals of glucose, fructose & mannose are similar -needle shaped crystals arranged like broom.

30. Osazone crystals Glucosazone – needle shaped Maltosazone - sun flower shaped Lactosazone – badminton ball/powder puff