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					               Carbohydrate chemistry

 Definition
 Nomenclature
 Cyclic form of sugar
 Optical isomerism
 Glycosidic link
 Polysaccharides
 Carbohydrate derivatives
                      Defination


 Carbohydarte are polyhydroxy
    aldehydes,polydroxyketones or compounds that can
    be hydrolysed to them
   Monosaccharides
   Disaccharides are
   Oligosaccharides
   polysaccharides
                   Nomenclature


 Based on the no. of carbons with the suffix –ose
    added.
   CnH2On,n= no. of carbons
   Triose= three carbons
   Tetrose= four carbon
   Pentose = five carbon
   Hexose= six carbon
                        cont.

 Nomenclature can also indicate the reactive groups.
 A) Aldoses are monosaccharides with aldehyde.
 B) ketoses are monosaccharides with containing a
  ketone group.
 Sugar with aldehyde=aldohexoses.
 System of numbering the carbon . The carbon are
  numbered sequentially with aldehyde or ketone
  group being on the carbon with the lowest possible
  number.
              Cyclic forms of sugar

 Chemical and physical properties of many sugars has
  shown that cyclic forms predominate over open-
  chain structure, both in liquid and solid state.
 Cyclic form of sugar = pyranoses; they resemble
  pyran.
 Frutose= Furanose.
 The intermolecular hemiacetals.When aldehyde
  react with alcohol. They are unstable compounds.
Open chain and cyclic form
               Optical isomerism

 Asymmetric carbons: carbohydrates contain
 asymmetric carbons, those bounded to four different
 atoms or groups of atoms. Because of this
 asymmetric ,carbohydrates are optically active,
 rotating the plane of polarized light.
                          Cont.

 If plane polarized light is rotated to the right
  (clockwise) ,the compound is dextrorotatory.(+).
 If plane polarized light is rotated to the left
  (counterclockwise) , the compound is called
  levorotatory. (-).
                  configuration

 The simplest carbohydrate are the monosaccharides
 trioses for e.g glyceraldehydes,which has two
 optically active forms designated L and D form
L- Glecarldehyde; D-Glyceraldehyde
                          Cont.

 A sugar may be Dextrorotatory or levorotatory
  irrespective of its D or L configuration.
 Anomeric carbon : is a new asymmetric carbon that
  is created by cyclization at the carbon bound to
  oxygen in hemiacetal formation.
 If the hydroxyl on the anomeric carbon is below the
  plane of the ring ,it is said to be in the alpha position,
  if is above the plane of the ring , it is said to be beta
  position
Cont.
                        Cont.

 In solution alpha and beta slowly change into an
 equilibrium mixture of both. This process is known
 as mutarotation.
                    Glycosidic links

 Acetals : Hemiacetals reacts with alcohols to form
  acetals.
 Glycosides: a sugar react with an alcohols to form an
  acetal known as glycoside.
 If the sugar residue is glucose, the derivative is a
  glucoside, if fructose, it is fructoside , if galactose , it
  is a galactoside.
 When R is another sugar , the gyloside is a
  disacchraide.
                         cont.

 Gylcosidic linkages : Reading from left to right.
  Therefore , sucrose has an alpha 1,2 glycosidic
  linkage.
 The disaccharides maltose possess an unattached
  anomeric carbon atom, which may have either the
  alpha or beta configuration. The glycosidic linkage in
  maltose must be in the aplha 1,4 glcosidic
  configuration.
maltose
                  Polysaccharides

 Amylose is a linear unbranced polmer of alpha units
  in a repeating sequence of α 1,4 – glycosidic linkages.
 Amylopectin is a branced polymer of a α D glucose
  with α 1,4 glycosidic linkages and with α 1,6
  branching points that occur at intervals of
  approximately 25 to 30 α D glucose residues.
 Glucogen is a major storage form of carbohydrates in
  animals found mostly in liver and muscles . It is
  highly branched form of amylopectin .
                         Cont.

 Cellolose is composed of chain of d- glucose units
  joined by Beta 1,4 linkages. The chains are
  exclusively linear (i.e unbranced).
 1. Cellulose is a structural polysaccharides of plants
  cells.
 2.Although cellulose forms a part of the human
  diet(i.e diet in vegetables and fruits).it is not
  hydrolyzed by human enzymes systems.
            Carbohydrates derivatives

 A. Phosphoric acid esters of monosaccharides
 1. Phosphorylation is the initial step in the
  metabolism of sugars.
 2. phosphorylation sugars such as d – glucose 1-
  phosphate are metabolic intermediates.
Phosphorylation
                        Cont.

 Amino sugars . In these a , hydroxyl group is
 replaced by an amino or an acetylamino group.
D acetylglucosamine
                         cont.

 1. Glucosamine is the product of hydrolysis of chitin,
  the major polysaccharides of the shells of insects and
  crustaceans.
 2. Galactosamine is found in the polysaccharides of
  cartilage, chondroitin sulphate.
                        Cont.

 Sugars acid : are produced by oxidation of the
  aldehydic carbon , the hydroxyl carbon , or both.
  Ascorbic acid (vitamin C ) is a sugar acid.
 Deoxy sugars include 2- deoxyribose , found in DNA
                  Sugar alcohols

 Monosaccharides , both aldoses and ketones may be
  reduced at the carbonly carbon to the corresponding
  polyhydroxy alcohols(sugar alcohols).
 Aldoses yield the corresponding alcohols , while
  ketoses forms two alcohols because a new
  asymmetric carbon is found in the process.
                         Cont.

 Commonly occuring aldoses and ketoses forms the
    following sugar alcohols:
   A. D-Glucose yields D sorbitol.
   B. D Mannose yields D mannitol.
   C. D Galactose yields dulcitol.
   D. D.Fructose,and ketose yields D mannitol and D
    sorbitol.
                        Cont.

 There are enzyme sysytem in humans tissues that
  can reduce monosaccharides to their corresponding
  alcohols.e.g
 The formation of D-Fructose from D glucose via D-
  sorbitol in seminal vesicle.
 In cases of galactokinase deficency ,excess galactose
  may be reduced to dulcitol in the lens of the eye.
                        Cont.

 Sugar alcohols are also normal constituents of cell
 components as for e.g ribitol which is the
 carbohydrates moiety of riboflavin, found in the
 electron carriers riboflavin phosphate and flavin –
 adenine dinucleotide.

				
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posted:11/23/2012
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