Carbohydrates Definition :
are macromolecules, consists of Carbon, Hydrogen and Oxygen. H and O are found in
same proportion as in water (H2O).
Biological Significance of Carbohydrates:
1- Carbohydrates are the major source of Energy.
2- Stores energy in form of glycogen in liver and muscles.
3- Component of cellular membranes (as well as organelles membranes). e.g. cellulose of
plant cell wall, and Actin for cuticle of insects outer bodies.
Types of Carbohydrate in living organisms : can be divided into 3 types
1-Monosaccharides: The simplest form of carbohydrates.
• Monosaccharide exists in form of (unbranched )chain, or in cyclic form (ring).
• Molecular formula is (CH2O)n, where n is number of C atoms and =3,4,5,6,7.
• Monosaccharides are classified by the number of carbon atoms: Trios (3 carbon
atoms), tetrose(4), pentose (5), hexose(6), heptose(7).
• The cyclic (ring) form can be either a pentose (5) or hexose (6) only.
• e.g. Glyceraldehyde (Triose)( C3H6O3), Ribose and deoxyribose (pentose) found in
nucleic acids.
Glucose and fructose (hexoses).
•2-Disaccharides:
Formed by binding of 2 units of monosaccharides by glycosidic bond (-O-) . Molecular
formula is C12H22O11.
* Maltose: 2 units of glucose , Joined together by glycosidic bond.
* Sucrose: Glucose + fructose ,Sucrose is table sugar we use as sweetener for food and drinks.
* Lactose: Galactose + glucose, it is milk sugar.
3-Poly saccharides:
Large molecules composed of repeating units of monosaccharides. Molecular formula is
(C6H10O5)n, where n = number of monosaccharides units.
A-Polysaccharides can be divided chemically to:1- Homo-polysaccharides: consists of
one type of monosaccharides.
2- Hetero-polysaccharides: consists of different types of monosaccharides, e.g.
Hemicellulose (present along with cellulose in almost all plant cell walls.)- Hyaluronic
acid.( is a substance that is naturally present in the human body )
B- Polysaccharides can be divided according to function to:
1- Structural Polysaccharides
2- Nutritional Polysaccharides
Cellulose units of glucose
linked by β- glycosidic bond,
unbranced and linear.
Glycogen (animal starch) units of glucose
linked by α- glycosidic bond. Branched.
Actin units of acetyl-glucose
amine. Forms the outer
Starch units of glucose linked by αglycosidic bond
1-banched called Amylopectine.
Slide
Features
(For read)
Nutritional
Polysaccharides
Glycogen in liver
Mucus in mucus
gland
‫المواد المخاطية في األمعاء‬
mucus in intestine
Nutritional
Polysaccharides
Starch granules in
potatoe.
Tissue parts
stained red
indicate
presence of
glycogen
Tissue parts
stained blue
indicate
presence of
Mucoid
substances.
Starch granules
stained dark.
Object
Reagents
and dyes
periodic
acid
Schiff
(PAS)
method
Alcian
blue
method
Gieson
Stain

Glycogen
(Animal
Starch)
Mucoid
Substance

(polysacch
aride
derivatives
)
Starch
Chemical Experiments
Detection of Carbohydrates
(1) Detection of Monosaccharides:
•Detection of Glucose and Fructose
1- In test tube, put 5 ml of sucrose solution (1%) , add 5 drops of HCl to hydrolysis sucrose
into glucose and fructose
2- Heat mixture of sucrose preparation in boiling water for 5 minutes.
3- Add 1 ml of NaOH solution to make solution slightly basic.
4- To detect Glucose (Fehling reaction): In test tube mix 1 ml of Fehling A + 1 ml Fehling B,
then add 5 drops of sucrose preparation from the previous steps and heat over flame for 5
minutes.
5- To detect Fructose (Silvanof reaction) : In test tube put 5 drops of sucrose preparation +
2 ml of silvanof reagent. Heat on flame for 6 min
Observation:
Sucrose solution with Fehling’s: Red brown precipitant
Sucrose solution with Silvanof: Bright red color
Results
Sucrose solution
Glucose
fructose
Fehling reagent
(+) Red brown ppt.
(-)
Silvanof
(-)
(+) Bright red solution
•2-Effect of Invertase enzyme on Sucrose Digestion and Hydolysis:
1- Prepare invertase enzyme extract by grinding 10 gm of yeast with 5 ml distilled
water and table sugar.
2- In test tube, put 2 ml of sucrose solution (2%) + 2 ml of Fehling reagent (1ml of Fehling
A and 1 ml of B), heat in 37˚C water bath for 6 min.
3- In new test tube, put 2 ml of sucrose solution + 2 ml of invertase extract and mix well.
Then put in for 15 min. Add 2 ml of Fehling reagent (A & B) , heat in boiling water bath
for 10 min.
Results
Sample
Mixture
without
Observation and Conclusion
enzyme ( - ) Reagent color does not change
(invertase)
No hydrolysis (Fehling does not react with sucrose)
With invertase
(+) Brown color, sucrose was digested and
hydrolysed into Glu and Fru ( Fehling reacts with