Types of Carbohydrates• Monosacchrides• Disaccharides Contain 2 monosacchride units• Polysacchrides Contain many monosacchride units 2
MONOSACCHARIDES Empirical formula: CH2O Monosaccharides contain:a) C=O group andb) at least two OH- groups C5H10O5 pentoses (e.g. ridose) C6H10O6 hexoses (e.g. glucose) They have between 3 and 6 carbon atoms. They have many structural isomers. Several carbon atoms are chiral and give rise to optical isomerism. Chain and ring structures are possible.
Monosaccharides• Three Carbons = Triose• Four Carbons = Tetrose• Five Carbons = Pentose• Six Carbons = Hexose 4
Monosaccharides• Aldoses are monosacchrides with an aldehyde group and many hydroxyl (- OH) groups.• Ketoses are monosacchrides with a ketone group and many hydroxyl (-OH) groups. 5
D notation O H C H C OH H C OH CH2OH Right = D 6
D-GLUCOSEThe form of glucose that is found in nature is known as D-glucose. To form the cyclic structure, connect the first and the Figure 1: Straight fifth carbon chain formula of D- (condensation) glucose.
Cyclic Structures• Monosaccharides with 5-6 carbon atoms form cyclic structures• The hydroxyl group on C-5 reacts with the aldehyde group or ketone group O o 8
β βD-glucose can cyclize in twoways forming either furanose orpyranose structures
D-Glucose CH2OH CH2OH o o OH β OH OHOH OH OH α OH OHα-D-Glucose β-D-Glucose 10
POLYSACCHARIDES o Monosaccharides can undergo condensation reaction to form disaccharides and polysaccharides. Condensation CondensationMonosaccharides Disaccharides Polysaccharides
POLYSACCHARIDES Amylose Straight chain α-1,4 Water solubleStarch α-glucose Amylopectin Branched α-1,4+α-1,6 Water insolubleGlycogen α-glucose More branched α-1,4+α-1,6 Water insolubleCellulose β-glucose Straight chain β-1,4+H-bonds Water insoluble Hydrolyzed by cellulose > found only in plant eating mammals > cannot be digested by humans
MAJOR FUNCTIONS OF POLYSACCHARIDES IN THE HUMAN BODYCarbohydrates have many uses:c)They provide energy: bread, corn, cereals, rice,potatoes, fruits.d)The store energy: starch is stored in the liver ofthe animals in the form of glycogen. Glycogen ishydrolyzed to glucose.e)They used as precursors for other importantbiological molecules (nucleic acids)f)They are used as dietary fibres: cellulose,lignin, pectin in fruits, grains, vegetables
Dietary fibreWater insolubleCellulose, ligninWhole grain foods, brown rice, carrots, tomatoesAbsorb waterBulk moving food through digestive systemWater solublePectinOatmeal, beans, peas,lentils, most fruitsFermented by bacteria to carboxylic acidsStabilize blood glucose levels (prevent diabetes)Stimulate production of antibodiesPrevent:ConstipationIrritable bowelObesityHaemorrhoids