Carbohydrates

Carbohydrates

1. Monosaccharides

   • Classified according to
     • Presence of aldehyde or ketone group
       • Aldoses: Glucose Mannose Galactose
       • Ketoses: Fructose.
     • According to number of carbon atoms
       • Trioses Tetroses Pentoses Hexoses
   • Derivatives
     • Sugar acids e.g: Glucoronic acid and gluconic and saccharic.
     • Deoxy sugars e.g: 2 deoxy ribose that is present in DNA
     • Amino sugars e.g: glucosamine and mannosamine
     • Sugar alcohol e.g: mannitol ribitol and xylitol(replace sucros table sugar)
       • artifical sweeteners
       • can be used to mask unpleasant aftertastes of some high intensity sweeteners
       • Not metabolized by oral bacteria, so no tooth decay
       • They do not brown or caramelize when heated

2. Oligosaccharides

   • Disaccharides
     • Maltose
       • 2 glucose D units linked together by alpha 1,4 glucosidic bond
       • Reducing sugar
       • Can be fermented
       • Maltose + H2O - Maltase -> 2 glucose units
     • Lactose
       • Formed of D glucose and D galactose linked by beta 1,4 galactosidic bond
       • Reducing sugar
       • Non fermentable
       • Lactose + H2O -Lactase-> glucos + galactose
     • Sucrose
       • Formed of D glucose and D fructose linked together by alpha 1-2 glucosidic bond
       • Non reducing sugar
       • Fermentable into ethyl alcohol and CO2
       • Sucros + H2O -Sucrase-> Glucose + Fructose

3. Polysaccharides

   • Homopolysaccharides(same sugar units)
     • Glucosans on hydrolysis gives glucose only (starch dextrin cellulose glycogen)
       • Starchs and dextrins
         • Present only in plants
         • Branched chain formed of D glucose units linked by alpha 1-4 glucosidic bond and alpha 1-6 at branches
         • Gives blue colour with iodine
         • Starch -Acid hydrolysis-> glucose units
         • Starch + H2O -Amylase enzyme-> Maltose+Dextrins
       • Cellulose
         • In plants only
         • Formed of D glucose units linked by beta 1-4 glucosidic bond
         • Cannot be digested by amylase in human and carnivorous
         • Not branched
         • Dietary fibers such as lignin and pectin
           • Prevent constipation
             • Add bulk to stool to stimulate intestinal wall
             • Absorb water which is drained into intestinal lumen increasing bowel movement
       • Glycogen
         • Main storage for glucose, resembles starch in structure but more branched
         • Present in liver and muscles. muscle selfish liver supplies to rest of the tissues
         • Gives pink colour with iodine
   • Heteropolysaccharides(sugar units+ other groups)
     • Neutral Heteropolysaccharides
     • Acidic heterpolysaccharides
     • Acidic Heteropolysaccharides(Mucopolysaccharides)
       • Sulfate free (Hyaluronic acid)
         • Present in ground substances of C.T. cartilage and tendon, its highly viscous so serves as lubricant in synovial fluid
         • N-acetylglucosamine + glucoronic acid connected by glycosidic linkages
       • Sulfate containing acidic mucopolysaccharides
         • Mucoitin sulfate
           • Present in sulfomucin of saliva and gastric juice
           • N-acetylglucosamine SULFATE + glucoronic acid
         • Chondroitin sulfate
           • resent in cartilages and tendons
           • N-acetylgalactoasmine sulfate + glucoronic acid
         • Heparin
           • Present in mast cells
           • It acts as an anticoagulant aby binding to the protein antithrombin III
           • glucosamine BISULFATE + glucoronic acid