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MHT-CET : Chemistry Entrance Exam

MHT - CET : Chemistry - Carbohydrates Proteins and Fats Page 1

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1.

Carbohydrates

 

The naturally occurring polyhydroxy aldehydes or ketones or substances which yield such compounds on hydrolysis are called carbohydrates.

 

 

Classification of Carbohydrates.
Carbohydrates are classified as sugars and non-sugars.

 

 

a) Sugars

  • Crystalline in nature
  • Soluble in water
  • Sweet to taste.

    Sugars are further classified as monosaccharides and oligosaccharides,

Monosaccharides

Oligosaccharides

o                                Basic units cannot be further hydrolysed.

i) Aldoses

                                                         Contains
group

                                                         Aldopentose
Contains 5 C - atoms. Example: Ribose C5H10O5

                                                         Aldohexose
Contains 6 C - atoms. Example: Glucose C6H12O6

ii) Ketoses

                                                         Contains
group

                                                         Ketopentose
Contains 5 C - atoms. Example: Ribulose C5H10O5

                                                         Ketohexose
Contains 6 C - atoms. Example: Fructose C6H12O6

                                 Can be hydrolysed to give 2 - 10 units of monosaccharides.

i) Disaccharides

                                                         2 molecules of monosaccharides of hydrolysis. Example: Sucrose C12H22O11

ii) Trisaccharides

                                                         3 molecules of monosaccharides on hydrolysis. Example: Raffinose C18H32O16

 

 

b) Non-sugars

Example: Starch, cellulose (C6H10O5)x

  • Amorphous in nature
  • Insoluble in water
  • Tasteless
  • On hydrolysis produce monosaccharides.

 

 

Preparation of Glucose (C6H12O6)

 

 

a]

From sucrose i.e., cane sugar (in laboratory)

 

 

 

b]

From starch (large scale preparation)

 

 

 

2.

Proteins

 

The naturally occurring nitrogen containing polymeric compounds of very high molecular weight containing recurring - CONH - group are called proteins.

 

 


Classification of Proteins:

 

 

a)

Simple Proteins: Examples: Albumin, globulin.

 

On hydrolysis, they give only a - amino acids.

 

 

 

i)

Globular Proteins: Example: Albumin
These proteins are spherical in shape and are soluble in water.

 

 

 

 

ii)

Fibrous or Structural Proteins: Examples: Fibroin, keratin.
These proteins have fibre-like structures and are insoluble in water.

 

 

 

b)

Conjugated Proteins: Example: Nucleoprotein.
On hydrolysis, they give
a - amino acids and some non-protein compound (prosthetic group).

 

 

c)

Derived Proteins: Examples: Polypeptides, peptones.
These proteins are formed by the treatment of some chemicals or heat on natural proteins.

 

 

 

 

 

Peptide Linkage
The - CONH linkage which joins a-amino acids in the structure of protein is known as a peptide linkage.
It is formed by the combination of the amino group of one
a-amino acid with the carboxyl group of the other a-amino acid.

 

 

 

 

 

 

 

Colour Test of Proteins

a)

Biuret Test

 

A protein solution is heated with 10% NaOH solution. A drop of aq. CuSO4 solution is added to the hydrolysed protein solution. A reddish - violet colour develops showing presence of peptide linkage.

 

 

b)

Millon's Test

 

Millon's reagent is a solution of mercurous nitrate and mercuric nitrate in dilute HNO3.
When a protein solution is warmed with Millon's reagent, a white precipitate is formed, which turns red on boiling. This shows the presence of phenolic
-OH group in the protein molecule.

 



 

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