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