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