Nucleic Acids: Structure & Bonding - Notes | Study Biology Class 11 - NEET

NUCLEIC ACIDS :

CHEMICAL COMPOSITION :

 Meischer discovered nucleic acids in nucleus of pus cell and called it ''nuclein''. The name nucleic acid proposed by ''Altaman''.

 Nucleic acids are polymer of nucleotides.  = Nitrogen base + pentose + phosphate 

On the basis of structure, nitrogen bases are broadly of two types :

1.   Pyrimidines – Consist of one pyrimidine ring. Skeleton of ring composed of two nitrogen and four Carbon atoms e.g. Cytosine, Thymine and Uracil.

2.   Purines – Consist of two rings i.e. one pyrimidine ring (2N + 4C) and one imidazole ring (2N + 3C) e.g. Adenine and Guanine.

Pentose Sugar :-

Nitrogen base forms bond with first carbon of pentose sugar to form a nucleoside. Nitrogen of first place (N₁)  forms bond with sugar in case of  Pyrimidines while in purines nitrogen of ninth place (N₉) forms bond with sugar.

Phosphate forms ester bond (covalent bond) with fifth carbon of sugar to form a complete nucleotide.

Types of Nucleosides and Nucleotides:

1.   Adenine + Ribose = Adenosine

      Adenosine + Phosphate = Adenylic acid

2.   Adenine + Deoxyribose = Deoxy adenosine

      Deoxy adenosine + P = Deoxy adenylic acid  

3.   Guanine + Ribose = Guanosine

      Guanosine + P =  Guanylic acid

4.   Guanine + Deoxyribose = Deoxy guanosine

      Deoxy  guanosine + P = Deoxy guanylic acid 

5.   Cytosine + Ribose  = Cytidine

      Cytidine + P = Cytidylic acid 

6.   Cytosine + Deoxyribose = Deoxycytidine

      Deoxycytidine  + P = Deoxycytidylic acid 

7.   Uracil + Ribose = Uridine

      Uridine + P = Uridylic acid    

8.   Thymine + Deoxyribose = Deoxy thymidine

      Deoxythymidine  + P = Deoxythymidylic acid