Cyclic form of sugar
Carbohydarte are polyhydroxy
aldehydes,polydroxyketones or compounds that can
be hydrolysed to them
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
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
The intermolecular hemiacetals.When aldehyde
react with alcohol. They are unstable compounds.
Open chain and cyclic form
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
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
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.
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.
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
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 –