Why Carbohydrates?

1. Why Carbohydrates? • Play a number of important roles in biochemistry: • Major energy sources • Play a key role of processes that take place on the surfaces of cells. eg. cell-cell interactions • Essential structural components of several classes organisms. Eg. Cellulose: components in grass and trees

2. Consist of 3 sub-classes - monosaccharide - oligosaccharide - polysaccharide * saccharide = 1 unit sugar, normally refers to glucose Carbohydrates

3. Carbohydrate • General formula – Cn(H2O) n • Only the simple sugars (monosaccharides) fit this formula. • Oligosaccharides and polysaccharides are based on the monosaccharides unit and have slightly different formula. • Oligosaccharides? • Polysaccharides?

4. Compounds containing C, H and O • Produced in plants by photosynthesis 6CO2 + 6H2O  C6H12O6 + 6O2 • All have C=O and –OH functional group. • The C=O may be as HC=O or by itself. • As HC=O( aldehyde) so the sugars are also known as aldoses . Just as C=O, the sugars are also known as ketoses.

5. Suffix – ‘ose’ indicates that molecule is a carbohydrate. • Major roles in energy metabolism ( energy storage and energy transport ) and structural component.

6. Monosaccharides -monosaccharides is a molecule of single sugar unit. e.gglucose, galactose, mannose, fructose, xylose • Are the simplest sugars • Can be used for fuel • Can be combined into polymers - Glucose, galactose, and mannose are 6C molecules or aldohexoses. - Xyloseis a 5C molecule/aldopentose.

7. D-Glucose • This is a Fischer Formula • 6C monomeric molecule • Is an aldohexose • D to denote the –OH on C5 is on the right side of the C chain

8. Emil Fischer ( 1852 -1919 ) was a German-born scientist who won the noble prize in chemistry.

15. Stereochemistry of monosacharides • Anomers :- Sugars that differ only in the configuration around the anomeric carbon (carbonyl becomes a new chiral; C1) • Epimers :- Sugars that differ only by the configuration at one C atom ( excluding the anomeric carbon )

16. Enantiomers :- Molecules that are superimposible mirror images of one another. • Isomers : Isomers are molecules with the same molecular formula, but different arrangements of atoms.

17. Stereoisomers : molecules that differ from each other only in their configuration ( three dimensional shapes )also called optical isomers. Glucose n Galactose. • Diastereomers :non superimposable,non mirror image stereoisomers. ( L- Threose with both D n L erythrose. )

18. The figures show the two isomeric forms that are mirror images of each other → stereoisomers. • The two forms differ in the position of –OH group bonded to the central C. • the mirror-image stereoisomers are also called enantiomers, • D-Glyceraldehyde and L-Glyceraldehyde are enantiomers. Fig. 16-1b, p.435

19. Epimers

20. Mirror image

21. diastereoisomers The aldotetroses have two chiral C ; C-2 and C-3. Therefore, the stereoisomers of aldotetroses are 22, or four possible stereoisomers. Diastereoisomers that differ from each other at only one chiral C are known as epimers. D-erythrose and D-threose are epimers. Fig. 16-3, p.437

22. Haworth projections formula

28. The most abundance monosaccharide in nature.

29. Glucose Anomers

32. Oligosacharides - oligosaccharides is a chain containing 2-10 sugar units. - Two sugar units also called Disaccharides. - The name is derived from the Greek word oligos, meaning "a few", and from the Latin/Greek word sacchar which means "sugar" - These sugar units join to one another by glycosidic linkages. - Maltose and Lactose: Alternative Glycosidic Linkages (1,4) - Sucrose: glucose-α-1,2-fructose

33. Examples • Maltose, a cleavage product of starch (e.g., amylose, is a disaccharides with an α(1,4) glycosidic linkage between the C1 hydroxyl of one glucose and the C4 hydroxyl of a second glucose. Maltose is the α anomer, because the O at C1  points down from the ring.

34. Sucrose, common table sugar, has a glycosidic bond linking the anomeric hydroxyls of glucose and fructose. Because the configuration at the anomeric carbon of glucose is α (O points down from the ring), the linkage is designated α(1,2). • Lactose, milk sugar, is composed of glucose and galactose with β(1,4) linkage from the anomeric hydroxyl of galactose.

35. Disaccharide Synthesis Energy + The reactions, the names of the sugars, and whether they are mono- or disaccharides is what you should know (also, “Glycosidic linkage”)

36. Dehydration reaction in the synthesis of maltose. The bonding of two glucose units forms maltose. The glycosidic link joins the number 1 carbon of one glucose to the number 4 carbon of the second glucose. Joining the glucose monomers in a different way would result in a different disaccharides. (a) CH2OH CH2OH CH2OH CH2OH O O O O H H H H H H H H 1–4glycosidiclinkage HOH HOH HOH HOH 4 1 H H H H OH OH O H OH HO HO OH O H H H H OH OH OH OH H2O Glucose Maltose Glucose CH2OH CH2OH CH2OH CH2OH O O O O 1–2glycosidiclinkage H H H H H HOH HOH H 2 1 H OH H HO H HO Dehydration reaction in the synthesis of sucrose. Sucrose is a disaccharide formed from glucose and fructose.Notice that fructose,though a hexose like glucose, forms a five-sided ring. H (b) HO H O O HO CH2OH CH2OH OH H OH H H H OH OH H2O Glucose Sucrose Fructose Figure 5.5

39. Reducing & Non Reducing Sugar • Sugars exist in solution as an equilibrium mixture of open-chain and closed-ring (or cyclic) structures. • In the open-chain form, the carbon atom that contains the C=O bond is called the carbonyl carbon. • Sugars that can be oxidised by mild oxidising agents such as Benedict's Solution, Fehling's Solution,and Tollen's Reagen are called reducing sugars because the oxidising agent is reduced in the reaction. • Reducing sugar: one that has a free aldehyde group and this aldehyde is easily oxidized.

40. + Ag (NH3)2 Being reduced Tollens’ agent

41. A non-reducing sugar is not oxidised by mild oxidising agents. • All common monosaccharides are reducing sugars. • The disaccharides maltose and lactose are reducing sugars. • The disaccharides sucrose is a non-reducing sugar (both anomeric groups are involved in glycosidic linkage)

42. Polysaccharides • are the complex carbohydrates • is a macromolecule, containing >1000 sugar units/monomers. • They are made up of chains of monosaccharides (the sugars) which are linked together by glycosidic bonds, which are formed by the condensation reaction.

43. The linkage of monosaccharides into chains creates chains of greatly varying length, ranging from chains of just two monosaccharides, which makes a disaccharide to the polysaccharides, which consists of many thousands of the sugars. • the molecule can be straight chain or branched. • e.g amylose, cellulose are straight. • e.g xanthan gum, amylopectin are branched.

44. the monomers can be of 1 type (homopolysaccharide) • e.g starch ( poly D-glucose) or • Mixed types (heteropolymers) • e.g xanthan gum which are glucose-glucose-mannose- glu.acid-mannose • the importance of glycosidic linkage: • β-glycosidic linkage: cellulose and chitin –structural material • α-glycosidic linkage: starch and glycogen – carbohydrate storage polymers in plants and animals

45. Xantham gum

46. Cellulose • Cellulose is a major component of plant cell walls. It is an unbranched polymer with about ten thousand glucose units per chain. • Hydroxyl groups (-OH) project out from each chain, forming hydrogen bonds with neighbouring chains which creates a rigid cross-linking between the chains, making cellulose the strong support material that it is.

47. Despite the combined strength of cellulose, it is fully permeable to water and solutes which makes it ideal for allowing water and solutes into and out of the cell. • It is the most abundant organic substance in the living world and it has been estimated that more than half the total organic carbon on the planet is in cellulose.

49. Cellulose Know the difference

50. Cellulose Cellulose is a Structural polysaccharide