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(1) Glycosidic - Monosaccharides in a polysaccharide chain are linked by a glycosidic bond. The bond is formed between two carbon atoms of two adjacent monosaccharides with loss of a water molecule. 

(2) Peptide bond: Amino acids in a polypeptide or protein are linked by a peptide bond, which is formed when the carboxyl group ie. COOH of one amino acid reacts with the amino (–NH₂) group of the next amino acid with the elimination of a water molecule . 

(3) Phosphodiester bond : In a nucleic acid the phosphate group and sugar are joined together by phosphodiester bonds. An bonds is formed between phosphate and pentose sugar molecule in a nucleotide. The bond is called phosphodiester bond because there is an ester bond on either side. 

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Structual formulae for ten small molecules.

PYRIMIDINES

Purines and pyrimidines are manufactured by isolation. They are used by various laboratories, hospitals and research centres.

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Polysaccharides are long chains of sugars containing monosachharides as building blocks. If it is composed of the same monosaccharide it is called a homopolymer like cellulose. Heteropolymers contains different monosaccharide units. For eg starch

Polysaccharides perform various functions -

(1) Source of energy - polysaccharides are broken down to produce energy in the cells. 

(2) Storage - The food is stored in the form of starch in plants and in the form of glycogen in animals.

(3)Structural support -  Cellulose is the structural material of plants.

(4) Protective covering - Exoskeleton of the arthropods are made of polysaccharide chitin. 

 

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The important properties of enzymes are: 

1. All enzymes are proteins. They are complex macromolecules with high molecular weight.

2.  They catalyse biochemical reactions in a cell. They help in the breakdown of large molecules into smaller molecules or bring together two smaller molecules to form a larger molecule.

3. They catalyse reactions at a high rate with the help of the active site. They lower down the activation energy and thus the reaction can proceed with ease. 

4.  Enzymes do not initiate a reaction but accelerate it. 

5. They are not used up in the reaction. 

6. Enzymes affect the rate and not the direction.

7. Most of the enzymes have a high turnover number that is the number of molecules of a substance that is acted upon by an enzyme per minute. 

8. Enzymes are specific in action.

9. Enzymatic activity is affected by changes in temperature, pH and concentration of the substrate.

 

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The different tests are

(a) For proteins - Biuret's test. If Biuret’s reagent is added to protein,and the colour of the reagent changes from light blue to purple it shows the presence of protein.

(b) For fats or oils - Grease and solubility of the test. 

(c) For amino acids - Ninhydrin test. If Ninhydrin reagent is added to the solution, then the colourless solution changes to pink, blue, or purple, it shoes the presence of amino acids. 

On testing the fruit juice, saliva, sweat and urine for the molecules we get the following result.

Substance	Biuret's test for protein	Grease or solubulity test for fats and oil	Ninhydrin test for amino acids.
1. Fruit juice	Gives positive result showing the presence of proteins.	Negative result showing absence of fats and oils.	Gives positive result for the presence of amino acids.
2. Saliva	Shows presence of proteins	Absence of fats and oils	Shows presence of amino acids.
3. Sweat	Absence of proteins	Presence of fats or opils	Absence of amino acids
4. Urine	Presence of proteins.	Not present	Presence of amino-acids.