Nucleic Acids

Friedrich Miescher  (1868) discovered the presence  of these compound  in protoplasm ,but Altman (1889) introduced the term Nucleic acid. These  acids are the largest  and most  complex compounds of carbon, hydrogen, oxygen, nitrogen and phosphorus, and of most biological  importance, two  type of these occur in biological systems viz.

1. Deoxyribonucleic acid (DNA) and

2. Ribonucleic acid (RNA)

Just as proteins and carbohydrates are polymers respectively of amino acid and monosaccharide units or monomers, nucleic acids are long  chain polymers of nucleotide   monomers (polynucleotide's). This polymerization is also dehydration  compensation  process i.e. nucleotide monomers link together by elimination  of water.

Each Nucleotide molecule is itself a complex compound of nitrogenous organic base  a pentose sugar and a phosphoric acid group linked together by dehydration condensation in two steps. First a base  and sugar molecule link by a n glycoside  bond to form a nucleoside. Then the C5 hydroxyl of the sugar molecule of nucleoside joins with a phosphate group to form a nucleotide molecule. Five nitrogenous bases enter into the composition of various nucleotides. these are of 2 kinds pyrimidine  derivatives with a single ring and purine  derivatives  with  a double ring structure. Pyrimidine derivatives are cytosine, Uracil and thymine. Purine derivatives are Adenine and Guanine. The pentose sugars o nucleotides are  also of two type deoxyribose and ribose .thus the nitrogenous bases, combining with pentose sugars and a phosphate group ,form eight types of nucleotide molecules as follows.

(1)   Cytosine + ribose sugar +phosphate = Cytidylic  acid

(2)   Cytosine +deoxyribose sugar +phosphate=Deoxycytidylic acid

(3)   Uracil+ riboxe sugar + phosphate = Uridylic acid

(4)   Thymine +deoxyribose sugar +phosphate= Thymidylic acid

(5)   Adenine + ribose sugar =phosphate=Adenylic acid

(6)   Adenine+ deoxyribose sugar +phosphate = Deoxyadenylic  acid

(7)   Guanine+ ribose sugar + phosphate = Guanuylic acid

(8)   Guanine+ deoxyribose sugar + phosphate= Deoxyguanylic acid