2. Introduction:
•They have a general formula – Cn(H2O)n , n>3.
•They contain 3 main elements ; carbon ,hydrogen and oxygen.
Definition: “carbohydrates are polyhydroxy aldehydes or ketones
and their derivatives.”
4. Classification of Carbohydrates:
1) Monosaccharides- cannot be broken down into smaller units by
hydrolysis. Sometimes called simple sugars.
a) Trioses – glyceraldehyde
b) Tetroses- Erythrose
c) Pentoses- ribose
d) hexoses- glucose
2) Disaccharides- can be broken down (hydrolyzed) into two
monosaccharide units. Ex -lactose, maltose etc,
3) Oligosaccharides- can be broken into three to six monosaccharide
units. Ex- Raffinose
4) Polysaccharides- composed of 7 or more mono-saccharide units .
a) Homo polysaccharides: Ex- Starch, Glycogen etc,.
b) Hetero polysaccharides: Ex- hyaluronic acid, heparin etc,
6. Reducing and non-reducing sugars:
•Reducing sugars: - a sugar which has a free aldehyde group or a free
ketone groupthat can reduce benedict’s reagent.
Ex.-glucose, lactose, maltose etc,
•Non-Reducing sugars: - a sugar which do not have a free aldehyde
group or a free ketone group and thus, cannot reduce benedict’s
reagent.
Ex.- Sucrose.
7. Mutarotation:
Mutarotation is the change in the optical rotation because of the change
in the equilibrium between α and β anomeric forms of glucose.
8. Disorders of carbohydrate metabolism:
•Glycogen storage disorders:
Glycogen storage disease (GSD, also glycogenosis) is the result of
defects in glycogen-synthesis or breakdown related enzymes
within muscles, liver, and other cell types. It can be genetic or
acquired.
Example- type-1disorder (Gierke’s disease)- due to defect of glucose-
6-phosphatase enzyme, cori’s disease etc,.
9. Qualitative tests or identification tests for carbohydrates:
1)Molisch’s test:
-test for carbohydrates.
Few drops Molisch reagent+ 2ml sample+ conc.H2SO4-
along sides of test tube: carbohydrates on dehydration by sulfuric acid
produce furfural which then condenses with the -naphthol resulting
in a red or purple-colored ring at the junction of 2 liquids.
2) Iodine test:
-test for polysaccharides.
2ml sample+iodine solution drop wise-
Iodine solution based on adsorption reacts with starch producing a
blue-black color.
10. 3) Barfoed’s test:
-test for monosaccharides.
2ml sample+5ml reagent+ boil 2min-
In Barfoed’s reagent, cupric acetate in acetic acid, is balanced so that is
can only be reduced by monosaccharides forming brick-red cuprous
oxide precipitate.
4) Seliwanoff’s test:
-test for ketoses.
2ml sample + 5ml reagent+ boil 2min-
When heated with reagent, ketoses are more rapidly dehydrated
than aldoses, a red color appears.
11.
12. 5) Benedict’s test:
-test for reducing sugars.
5ml Benedict's reagent +few drops sample-
The reducing sugar here reduces the cupric ions in
these test solutions to cuprous ions, which then forms a brick red
copper oxide precipitate.
6) Fehling’s test:
-test for reducing sugars.
5ml Fehling’s reagent+ few drops sample-
The reducing sugar here reduces the cupric ions in these test solutions
to cuprous ions, which then forms a brick red copper oxide
precipitate.
14. 7) Osazone test:
• microscopic test for crystalline structure of carbohydrates.
•Osazones are formed when the sugars react with a
compound known as phenylhydrazine hydrochloride at
boiling point.
•Osazone crystals have a characteristic shape nder the light
microscope, ths help in identification of sugar type.
