CARBOHYDRATE

Introduction

Carbohydrates are one of the three major classes of biological

molecules.

The body get its energy from three main classes of food :

1. Carbohydrates ( consider the most important source of energy )

2. Protein

3. Fat

functions

Variety of important functions in living systems:

Energy supply, particularly for the brain in the form of glucose

through oxidation and regulation of blood glucose

they supply carbon for the synthesis of cell components

Flavor and Sweeteners

Dietary fiber

Cellular and protein recognition

Carbohydrate

Polyhydroxy aldehyde or polyhydroxy ketone

The common chemical formula for carbohydrates is Cn(H2O)n

the ratios are usually:

1 Carbon: 2 Hydrogens: 1 Oxygen

Carbohydrates are carbon compounds that contain large quantities of

hydroxyl groups.

Carbohydrates are chemically characterized as:

1. Poly hydroxy aldehydes

2. Poly hydroxy ketones.

Sugars that contain an aldehyde group are called Aldoses.

Sugars that contain a keto group are called Ketoses.

C HHO

C OHH

C OHH

CH2OH

CH2OH

C O

D-fructose

C

C OHH

C HHO

C OHH

C OHH

CH2OH

D-glucose

OH

Carbohydrate

Carbohydrate

Carbohydrates also can combine with lipids to form

glycolipids .

With proteins to form glycoproteins.

classification

Monosaccharides

contain a single polyhydroxy aldehyde

or ketone unit (glucose, fructose).

Disaccharides

consist of two monosaccharide units linked together by a

covalent bond ( sucrose which

hydrolyzed to glucose and fructose.

Oligosaccharides

contain from 3 to 10 monosaccharide units

( raffinose)

Polysaccharides

contain very long chains of hundreds or

thousands of monosaccharide units. (cellulose, glycogen,

starch).

Classification of carbohydrate

A. monosaccharide:

The basic unite of carbohydrate

Monosaccharides are classified according to the number of carbon

atoms they contain:

3 triose

4 tetrose

5 pentose

6 hexose

E.g.: glucose, fructose.

Glucose is aldohexose

Fructose is ketohexose

Aldohexose: hexose is a monosaccharide with six carbon atoms, having

the chemical formula “C6H12O6”. An aldohexose is a hexose with an

aldehyde group on one end.

ketohexose: is a ketone-containing hexose (a six-carbon

monosaccharide).

Classification of carbohydrate

aldehyde

ketone

Classification of carbohydrate

B. Disaccharides :

Disaccharides consist of two monosaccharide units

linked together by a covalent bond

Example of disaccharide :

1. Lactose ( milk sugar)= galactose +glucose.

2. Maltose (malt sugar)= Glucose + Glucose .

3. Sucrose ( table sugar) = glucose + fructose .

Classification of carbohydrate

Lactose intolerance is the inability of adults to digest lactose, a sugar found in

milk or dairy products, causing side effects. It is due to a lactase deficiency, or

hypolactasia. Congenital lactase deficiency .

Lactose intolerant individuals have insufficient levels of lactase, an enzyme that

catalyzes the hydrolysis of lactose into glucose and galactose, in their digestive

system

Classification of carbohydrate

Classification of carbohydrate

Lactose Galactose + Glucose.

Maltose Glucose + Glucose

Sucrose glucose + fructose

C. Oligosaccharides:

contain from 3 to 10 monosaccharide units

D. Polysaccharides:

contain very long chains of hundreds or thousands of

monosaccharide units E.g. : cellulose, glycogen, starch

PHYSICAL PROPIRTIES

A. Monosaccharide :

Most monosaccharide's have a sweet taste

(fructose is sweetest; 73% sweeter than sucrose).

They are crystalline solids at room temperature.

They are extremely soluble in water

B. Disaccharide :

These are crystalline, water-soluble, sweet taste.

It is a white, odorless

PHYSICAL PROPIRTIES

C. Polysaccharide :

starch is a white, tasteless and odorless powder

Starches are usually insoluble in water because of the high

molecular weight, but they can form thick colloidal suspensions

with water. (Absorb water but do not dissolve in water)

PHYSICAL PROPIRTIES

Fructose LACTOSE

STATE Crystalline Powder

Color White White

Test Sweet

73% sweeter than

sucrose

sweet

Flammability Flammable Flammable

Solubility Extremely soluble

in H2O

Soluble in H2O

Effect on L.P neutral neutral

PHYSICAL PROPIRTIES

MALTOSE sucrose STARCH

STATE Crystalline Crystalline Powder

Color White White white

Test Sweet test Sweet test tasteless

Flammability Flammable Flammable Flammable

Solubility soluble in H2O Soluble in

H2O

inSoluble in

H2O

Effect on L.P neutral neutral neutral

PHYSICAL PROPIRTIES

CHEMICAL TEST

Chemical test

General test

Molisch’s test

Oxidation test

1) Fehling test

2) Benedict’s test

3) Tollens’ test

4) Barfoed's Test

Specific test

1) Seliwanoff's Test

2) Iodine solution test

General test:

Molisch’s test :

Use to distinguish between carbohydrates and non-carbohydrates .

procedure: 1 ml of carbohydrate solution + 3 drops Molisch reagent

+1 ml conc.H2SO4 (carefully added on the wall of tube) .

Result: a purple ring forming at the interface between the denser

sulfuric acid and the less dense test solution above .

CHEMICAL TEST

Oxidation tests:

1) Fehling test

procedure:

few mg of carbohydrates + 2 ml of Fehling reagent A&B then warm in water bath for 2.

Result :

change in blue color

All carbohydrates give +ve result except sucrose & starch

sucrose starch

Oxidation tests:

2) Benedict’s test

procedure:

2ml of carbohydrates + 2ml of Bendict’s soultion then

warm in water bath for 2-3 min.

Result :

Increasing amount of reduction of the sugar

Green ,orang, red ,brown

All carbohydrates give +ve except sucrose & starch

CHEMICAL TEST

sucrose starch

Oxidation tests:

3) Tollens’ silver mirror test

procedure:

1 ml of carbohydrates+ 1 ml of Tollens’ reagent ;then

warm in water bath for 2-5 min

Result:

make silver mirror Except sucrose & starch

CHEMICAL TEST

sucrose starch

Oxidation tests:

4) Barfoed's Test

To differentiate between mono- & disaccharide

procedure:

1ml of carbohydrates +3ml of Barfoed's reagent. The

solution is then heated in a boiling water bath for 3-10min.

Result :

formation of a reddish precipitate within three minutes.

+ve fructose

-ve starch, sucrose , maltose & lactose

CHEMICAL TEST

fructose

Specific tests for ketones sugar :

Seliwanoff's Test

Procedure:

1ml of carbohydrates +2 ml of Seliwanoff's reagent (a

solution of resorcinol and HCl). The solution is then

heated in a boiling water bath for 3-6 min.

Reuslt :

Give red color +ve fructose & sucrose

CHEMICAL TEST

fructose sucrose

Specific tests:

Iodine solution test :

Producer :

few mg of starch + 1ml of iodine solution

Result:

A dark blue color

CHEMICAL TEST

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