Carbohydrates and Carbohydrate metabolism (Chemistry of Carbohydrate )

1. Carbohydrates and Carbohydrate metabolism (Chemistry of Carbohydrate ) • Objective: • Understand classification and structure of carbohydrates • Understand multistep sequences (pathways) for carbohydrates metabolism. • Study the metabolic disorders in carbohydrates metabolism.

2. Carbohydrates and Carbohydrate metabolism (Chemistry of Carbohydrate ) • Carbohydrate: They are polyhydroxy aldhydes or ketones or any substances derived from them. OR • Compounds that contains at least 3 carbon atoms, a number of OH group, in addition to aldhyde or ketone • Formula for simple is (CH2O)n .

3. Carbohydrates • Importance and distribution of CHO in animal and plant tissue: • Plants: • (a) Cellulose: which form the frame work of the plant and has supporting action. • (b) Starch: Which is the stored form of CHO.

4. Carbohydrates • Classification of CHO: • (1) Monosaccharide: They are the simplest units of CHO, cannot hydrolyzed to the simpler form. • They can be classified according to either number of carbon atoms, or whether they contain aldhydes or ketons.

5. Carbohydrates (Monosaccharide) • (1) according to number of carbons: • Trioses:Ex.Glyceraldehydes (aldotriose) Ex. Dihydroxyacetone ( ketotrioses) • Tetrosis: Ex. Erythrose (aldotetrosis) Ex. Erythulose (ketotetrosis) • Pentoses:Ex. Ribose (aldopentosis) Ex. Ribulose (ketoopentosis) • Hexoses: glucose , fructose , galactose, mannose

6. Carbohydrates (Monosaccharide), Stereoisomerism • Asymetric carbon atom: A carbon atom that attached to four different atoms or groups of atoms. • Any substance containing asymetric carbon atom, it has two different optically active isomers. • Isomers: Compounds that have the same chemical formula but have different structure. Ex. Glucose, fructose, mannose, galactose.

7. Monosaccharide, Stereoisomerism • Epimers: Compounds that have the same chemical formula but differ in configuration around one carbon atom. Ex. ( D. glucose, D galactose C-4 not galactose and mannose) • Enantiomers: A special type of isomers is found in the pairs of structure that are mirror images of each other.( L. glucose, D. glucose) • D.glyceraldhyde: in which OH group attached to asymmetric C atom is towards the right. • L.glyceraldhyde: in which OH group attached to asymmetric C atom is towards the left.

8. Chemistry of Carbohydrate Stereochemical relations in carbohydrates were explored by Emil Fischer, who also devised a way to represent these molecules.  Fischer projection

9. H HO HO H H H H HO H H H H HO H H H H HO HO H H H HO H H –C=O –C–OH –C–H –C–OH –C–OH CH2OH –C=O –C–H –C–H –C–OH –C–OH CH2OH –C–OH –C=O –C–H –C–OH –C–OH CH2OH –C=O –C–OH –C–H –C–OH –C–OH CH2OH –C=O –C–OH –C–H –C–H –C–OH CH2OH In Fischer projection: Chiral C farthestaway from highest oxidized C has OH to right D-sugar. In Haworth projection:if C1-OH andC5-CH2OH on same side of ring = b, if on different sides = a(anders, alternative) b a Important Monosaccharides D-Glucose D-Galactose D-Mannose D-Fructose If only one of several stereocentres in a molecule is diferent, such isomers are epimers.

10. Cyclization of monosaccharide • The simple chain formula fails to explain the many reaction so, • Less than 1% of each of monosaccharides are found in a ring form, in which the aldhyde or keton group has reacted with an alcohol group in the same sugar. • Formation of the ring results in the creation of anomeric carbon atomat C-1 of an aldose and on C-2 of a ketose • These structure are designated the α & β configuration of the sugar. • If the remaining OH is on the right  α- sugar • If the remaining OH is on the left  β- sugar

11. Cyclization of monosaccharide • Mutarotation: The cyclic α & β anomers of sugar are in the equilibrium with each other, and can be spontaneously inter-converted in a process called mutarotation. • Representation of sugar conformation: (1)Fisher projection. (2)Haworth projection

12. H H HO H H –C=O –C–OH –C–H –C–OH –C–OH CH2OH Cyclization of monosaccharide b a Fischerprojection D-glucose open chain D-glucose ring form a-D-glucose Haworth projection a-D-glucose Chair conformation anomeric C

13. Chemistry of Carbohydrate • Reducing sugar: If the O2 of anomeric C- atom is not attached to any other compound, that sugar is a reducing sugar • A reducing sugar can react with the chemical reagent (Ex. Bendict solution& fehling solution) and reduce the reactive compound, with the anomeric C- atom is oxidized.

14. Important Monosaccharides

15. Disaccharide & polysaccharide • Disaccharides: These are formed by condensation of 2 molecules of monosaccharide by a glycosidic linkage. • oligosaccharides: contain from3 to about 12 of monosaccharide units. • polysaccharides: contain more than 12 of monosaccharide units.

16. Disaccharides Lactose Gal-b-1-4-Glu Maltose Glu-a-1-4-Glu Sucrose Glu-a-1-b-1-Fru

17. polysaccharide • Starch: It is the most important polysacharide. It is a polyglucose, a-1-4 linked. Ther are two main components: amylose – linear, ca. 500 – 20 000 linked glucose units amylopectin – branched through a-1-6 bonds every ~25 AGU • glycogen : body polysachharide: similar to amylopectin, higher branched • Cellulose: is composed of b-1-4 linked glucose units. This bond cannot be cleaved by our digestive enzymes. Important part of cell walls and dietary fibre.

18. Polysaccharides – Starch, glycogen a-1-6 branch pointin glycogen

19. Polysaccharides - Cellulose Stability of cellulose is increased through formation of crystalline regions with extensive hydrogen bonding

20. Complex carbohydrates • CHO can also attached by glycosidic bonds to non-CHO structure (a glycone) (Ex. Purine and pyrimidine as in nucleic acids, aromatic ring as those found in steroid & bilirubin, proteins as glycoproteins& glycosaminoglycans, and lipids as in glycolipids) to form glycosides. • O- and N- glycosides: If the group on the non-CHO is an OH group, the structure is an O- glycosides, whereas If the group on the non-CHO is an NH2 group, the structure is an N- glycosides.

21. The Aldoses C3 – C6 CHO E T RAXL AllAltruists Gladly Make Gum In Gallon Tanks

22. Dihydroxyacetone The Ketoses C3 – C6 Related Aldose+ ending “ulose“ Related Aldose+ ending “ulose“ P F S T

23. ~ 35 % Furan Pyran ~ 65 % < 1 % Glucose structure in solution Pentoses and hexoses can adopt two ring structures: 5-membered (Furanoses, after furan), and 6-membered (Pyranoses, after pyran). Glucose is in equilibrium between two pyranose forms. At equilibrium, there is ca.65 % b-D-Glucopyranose, ca. 35 % a-D-Glucopyranose, and <1 % of the open-chain form.

24. Fructose structure in solution Fructose adopts a furanose structure, preferring the a-anomer.

25. Other roles and modifications of carbohydrates In addition to their role as fuel molecules, carbohydrates are important molecules as: - building blocks of nucleic acids - antigens (blood groups, cellular interaction through glycosylated surface proteins) - glycosylation of proteins  quality control system for protein folding - glycosylation also determines functional properties of proteins - metabolic intermediates and specialised molecules