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Cyclic Form of Monosaccharides 1. Glucose 2
3
4
5
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2. Galactose 7
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3. Fructose 9
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Reactions of hexoses Hexoses which are either aldoses or ketoses have reducing properties. This reducing property of hexoses is the basis of the test for sugar in urine or blood. Gluconic acid 12
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Reduction of Monosaccharides Note: Accumulation of sorbitol in the eye is a major factor in the formation of cataracts due to diabetes. 15
Fermentation In the presence of yeast (or enzymes of yeast) glucose forms ethanol and carbon dioxide Fructose can ferment but galactose can not. Pentoses do not ferment in the presence of yeast. 16
Formation of Phosphate Esters Glucose forms phosphate esters at carbons 1, 6 17
Amino Sugars 18
Amino Sugars Amino sugars contain an -NH 2 group in place of an -OH group – only three amino sugars are common in nature: D- glucosamine, D-mannosamine, and D-galactosamine
Protein-Sugar Interactions When the glucose level in the blood is elevated over a period of time, normal hemoglobin binds to glucose covalently. The amount of glucosylated hemoglobin HbA 1 c in blood is used as a measure of the effectiveness of blood glucose control in a diabetic patient. The concentration of HbA 1 c directly reflects the elevation of blood glucose over the preceding several days. 20
In diabetic patient HbA 1 c is about 7 – 11% of the total hemoglobin (HbA) In nondiabetic person this value ranges 4 – 6%. 21
22 The word epimer means each of two isomers with different configurations of atoms around one of several asymmetric carbon atoms present. In chemistry, epimers are diastereomers that differ in configuration of only one stereogenic centre.
23 The sugars α-glucose and β-glucose are epimers. In α-glucose, the -OH group on the second (anomeric) carbon is in the direction opposite the methylene group on carbon C-6 (in the axial position). In β-glucose, the -OH group is oriented in the same direction as the methylene group (in the equatorial position).sugarsmethylene groupaxial α-D-glucose β-D-glucose
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