Carbohydrates 2 - Disaccharides Ⅰ

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Its early in the morning and you just woke up. You are thirsty for a glass of milk. Afterwards you have those favorite cornflakes of yours covered in honey for breakfast (Now I’m really hungry πŸ˜‚). What does the milk and honey have in common? …………. You guessed right. Disaccharides. We are going to learn what they are, how they form and their functions in this article.


Sucrose is the most abundant disaccharide. It is formed by the bonding of one glucose and one fructose molecule through a glycoside bond. Using sucrose as an example let us understand what disaccharides are.

The structural formula of sucrose is given below,


Glucose and Fructose have the same chemical formula C6H12O6 but glucose is an aldehyde and fructose is a ketone therefore they are functional structural isomers of each other because thy have 2 different functional groups this results in the change of shape of ring structure.

The reaction involved in forming a sucrose molecule is called a condensation/dehydration reaction since a H2O(l) is formed as a byproduct and the reverse reaction in which a sucrose molecule is dissociated/decomposed back into glucose and fructose is called hydrolysis. Why? Since a H2O molecule is dissociated and added into the monosaccharides [ as a result the name hydrolysis – lysis as in breaking]

Through this we can come to understand the chemical composition of a disaccharide, its chemical formulae and the general formula assigned in identifying a disaccharide which is,

CX (H2O) x-1

The removal of a H2O molecule is the reason for that X-1.

X = no. of C atoms

(X-1) = no. of C atoms – 1

E.g.:

D

D
Glucose + Fructose             →                 Sucrose

D

D
C6H12O6 + C6H12O6             →              C12H22O11


From our formula we can obtain the same result,

CX (H2O) x-1                             x= 6+6=12

Therefore C12(H2O)12-1 = C12(H2O)11 = C12H22O11

Continued in Carbohydrates 2 - Disaccharides Ⅱ.......



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