Carbohydrate chemistry_1_

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					               Carbohydrate chemistry

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

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

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

 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
              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
 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.

 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. (-).

 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

 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

 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
 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

 Gylcosidic linkages : Reading from left to right.
  Therefore , sucrose has an alpha 1,2 glycosidic
 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

 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 .

 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
 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.

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

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

 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.

 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

 There are enzyme sysytem in humans tissues that
  can reduce monosaccharides to their corresponding
 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.

 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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