Medical Lecture Notes

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Thursday, 4 January 2018

Properties of monosaccharides :

Properties of monosaccharides :

Physical properties :

  1. all monosaccharides are soluble in water .
  2. all monosaccharides show the property of optical activity.
  3. all monosaccharides can exist ina β forms.

 Chemical properties :

  1. oxidation :oxidation of sugars gives acids
  2. reduction : reduction of carbonyl group gives the corresponding alcohol.e.g. glucose gives sorbitol ,ribose gives ribitol, galactose gives galacticol ect.
  3. Reducing sugars : sugars containing free aldehyde or ketone group can reduce other reagents e.g.they can reduce cupric ions of fehling,s and Benedict,s reagents into cuprous ions:   Cuporic (blue )+ sugar ® cuprous(red)+ oxidizd sugar .These tests are one of the earliest tests for sugar detection in urine of diabetic . These tests are nonspecific , because these reagents can be reduced also other hexoses or other reducing compounds as vimtamin C .
  4. Reactions of phosphoric and sulfuric acids :  Reaction of phosphoric acid with monosaccharides gives phosphate esters e.g. glucose gives  glucose-6- phosphate and glucose-1- phosphate.phosphorylated sugars  are important intermediates in carbohydrate metabolism .Reactions of sulfuric acids :This acid is a dehydrating agent, removing 3 molecules of H2Ofrom the sugar giving a comound called furfural .The compound can condense with a - naphthol to give a violet ring .This is the idea of Molish,s test. A general test for all carbohydrates .
  5. fermentation : fermentation is the action of bacterial or yeast enzymes on carbohydrate fermentation of sugars give ethyl alcohol and CO2  . All D – monosaccharides are fermentable . C6H12O6®2CH3- CH2-OH+2Co2
  6. Osazone formation : Osazones are characteristic crystals resulting from the reaction of sugars with phenylhydrazine All sugars having free carbonyl group can from osazone crystals.

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