Download Oxidation Oxidation of aldoses forms acids as end products . CHO

Oxidation
Oxidation of aldoses forms acids as end products .
CHO
H-C-OH
OH-C-H
H-C-OH
(O)
H-C-OH
(O)
CH2OH
(O)
CHO
COOH
COOH
H-C-OH
H-C-OH
HO-C-OH
H-C-OH
HO-C-OH
HO-C-OH
H-C-OH
H-C-OH
H-C-OH
H-C-OH
H-C-OH
H-C-OH
COOH
COOH
CH2OH
Glucoronic Acid
Glucaric Acid
Gluconic Acid
Oxidation of the aldehyde group form aldonic acids . However , if
the aldehyde group remains intact and primary alcohol group at the
opposite end of the molecule is oxidized , uronic acids are formed .
Reduction
The monosaccharides may be reduced to corresponding alcohols by
reducing agents like agents like sodium amalgam .
2[H]
CHO
CH2OH
R
R
H2C –OH
2[H]
H2-C-OH
C=O
H-C-OH
R
Aldosugar
R
Ketosugar
Glucose yields sorbitol , galactose yields dulcitol , and fructose
yields mannitol and sorbitol .
Disaccharides
The disaccharides are carbohydrates that can be hydrolysed into
two units of monosaccharides . Sucrose is a non – reducing sugar
while lactose and maltose are reducing carbohydrates .
Maltose ( 2 Glucose Units )
Maltose consists of two molecules of D- glucose joined by a ( 1,4 ) –
glycosidic linkage . Maltose or malt sugar dose not occur in free
state but is formed as an important transitory intermediate product
of the digestion of starch into glycogen and glucose .
CHO
H-C-OH
H-C-OH
HO-C-H
H-C
H-C
H-C-OH
H
Maltose
O
H-C
H-C-OH
HO-C-H
H-C-OH
H-C
H-C-OH
H
Hydrolysis
O
H-C-OH
[HOH]
HO-C-H
H-C-OH
H-C-OH
H-C-OH
H
2 Glucose Units
Lactose ( Glucose Plus Galactose )
H
OH
H-C
H-C-OH
HO-C-H
C
CHO
H-C-OH
H-C-OH
O HO-C-H
O Hydrolysis
[HOH] HO-C-H
O
H-C
HO-C-H
H-C
H-C
CH2OH
CH2OH
Lactose
CHO
+ H-C-OH
HO-C-H
HO-C-H
H-C-OH
CH2OH
H-C-OH
H-C-OH
H-C-OH
CH2OH
Glucose
Galactose
Lactose occurs in mammalian milk . It is a reducing sugar .
Sucrose ( Glucose Plus Fructose )
Sucrose is widely distributed in plants . In the case of sugar cane ,
sugar beets and sugar maples , the concentration is sufficient for
commercial production . Sucrose is not a reducing sugar as both the
– CHO and < C=O group are involved in linkage and are not free
Polysaccharides
Starch
Starch is the major form of carbohydrate in plants . It usually occurs
in the form of compact insoluble grains inside the plants cells . The
starch grains are composed of two different properties , namely
amylase and amylopectin .
Amylose
A polysaccharide in which glucose units are joined in α – 1,4 –
glucoside linkages to form long slender chains .
The molecular weight of amylase is 60,000 corresponding to a chain
of 300 to 400 glucose units . Amylose is soluble in water and is less
viscous than starch .
Amylopectin
This polysaccharide possesses the same basic chain as amylose but
they are larger molecules . They have molecular weight as high as
2,00,000 or more m corresponding to 1000 to 1300 glucose units
G
G
G
G
G
G
G
G
G
G
G
G
G
G
GGGGGGGGGGGGGG
G
G
G
G
G
G
G GGGG
G
G
G
They are highly branched and soluble in warm water .
Hydrolysis of Starch
Starch which is compound of several glucose units is hydrolysed to
form first , maltose and finally glucose molecules .Hydrolysis of
starch can be brought about by both enzymes and acids . Enzymes
which hydrolyse starch are amylases , and they are present in saliva
as ptyalin and in pancreatic juice as pancreatic amylase . Amylase
acts on starch , hydrolyzing them into fragments of dextrins , and
ultimately to maltose molecules . They act at the 1-4 Glucosidic
linkages . The products of hydrolysis are given below :
Starch
Soluble Starch
Amyladextrin + Maltose
Erythrodextrin + Maltose
Achrodextrin + Maltose
Maltose + Maltose
Test of Starch
Starch will form a blue coloured complex with Iodine . This colour
disappears on heating but reappears on cooling . Test for
carbohydrates ( Molisch test ) 2 ml of the unknown solution , add 2
drops of fresh 1% α naphthol reagent and mix .Pour 2ml of con
H2SO4 so as to form a layer below the mixture .A red violet ring
indicates carbohydrate .
Glycogen
This is the major carbohydrate reserve in animals . In most
mammals deposits of glycogen are maintained especially in the
liver and in the skeletal muscles .The structure of the glycogen is
essentially the same as amylopectins , except that there is much
more extensive branching . This gives an increased solubility.
Glycogen is quite readily put into suspension even in cold water .
Cellulose
Cellulose forms the chief constituent of the structure of the cell
wall of plants . It is similar in structure to amylase , except that all
of the glucose are held together by β- 1-4 glucoside linkages .It is
highly insoluble and resistant to hydrolysis . There is no enzyme in
the human beings to break the β 1-4 glycosidic linkage . It therefore
passes through the human digestive tract without being attacked
by the enzymes . Cellulose forms the bulk of faecal matter . When
cellulose is not sufficient in the diet , constipation results . In
industry , cellulose is used for manufacture of rayon and explosives
.
Dextran
Dextran is a polysaccharide , closely related to starch and glycogen .
It has a molecular weight of approximately 50,000 . It is synthesized
from sucrose by certain bacteria . It is used as a blood substitute in
extensive loss of blood .
Inulin
It is a polysaccharide , each molecule of which is composed of
about 80-D- fructose unite. It occurs as a reserve carbohydrate in
the tubers and roots of chickory , dahlia dandelions and in the bulb
of onions and garlic . It is a white crystalline powder , sweet to
taste . It is readily soluble in hot reducing property . Inyulin is not
hydrolysed by enzymes of the gastrointestinal tract and does not
undergo any metabolic change in the body . When injected
intravenously , it is excreted quantitatively by glomerular filtration
within a short time . It dose not undergo any reabsorption in the
.This property of Inulin clearance is made use of in the
determination of the rate of glomerular filtration or Inulin
clearance in an individual ( urine ).
Mucopolysaccharides
Proteoglycans or carbohydrates containing uronic acid and amino
sugars present in connective tissues. Mucopolysaccharides
represent a variety of polysaccharides present largely in the ground
substance of connective tissue along with mucoproteins . They are
acidic substances containing aminosugars or their derivatives . They
are divided into the following sub-groups .
a. Neutral mucopolysaccharides , such as immunologically
important blood group substances , which contain only an N- acetyl
hexosamine and a hexose .
b . The second group has a hexuronic acid ( e.g. D- glucose acid)
along with an N- acetyl hexosamine – The group includes hyaluronic
acids which are found as components of connective tissues . They
are straight chain polymers with D- glucoronic acid and Nacetylglucosamine alternatively in the chains .
c. The third group is a complex one in which a polysaccharide may
contain hexoses , aminosugars ( free and acetylated ) hexuronic acids
and sugar sulphates . Examples are chondroitin s of cartilage ( Nacetylgalactosamine , glucoronic acid and sulphate esters of these
sugars ) and heparin , the natural anticoagulant of blood ( Glucosamine
N- sulphate m glucoronic acid and their sulphate esters ) .
Glycosidic linkages involving uronic acids aminosugars are very resistant
to hydrolysis and hence polysaccharides containing these unites are
extremely stable and present where chemical resistance and physical
strength are needed , e.g. in skin , connective tissues , insect
exoskeletone , umbilical cord , etc .