Nucleic Acids James Dewey Watson Born in Chicago, Illinois, in , Dr Watson received his Ph.D. ( ) from Indiana University in Zoology. He is best known for his discovery of the structure of DNA for which he shared with Francis Crick and Maurice Wilkins the Nobel prize in Physiology and Medicine. They proposed that DNA molecule takes the shape of a double helix, an elegantly simple structure that resembles a gently twisted ladder.
The rails of the ladder are made of alternating units of phosphate and the sugar deoxyribose; the rungs are each composed of a pair of purine/ pyrimidine bases. This research laid the foundation for the emerging field of molecular biology . The complementary pairing of nucleotide bases explains how identical copies of parental DNA pass on to two daughter cells. This research launched a revolution in biology that led to modern recombinant DNA techniques.
Complete hydrolysis of DNA (or RNA) yields a pentose sugar, phosphoric acid and nitrogen containing heterocyclic compounds (called bases). In DNA molecules, the sugar moiety is b -D- -deoxyribose whereas in RNA molecule, it is b -D-ribose. . .
Chemical Composition of Nucleic Acids Uracil (U) Thymine (T) Cytosine (C) DNA contains four bases viz. adenine (A), guanine (G), cytosine (C) and thymine (T). RNA also contains four bases, the first three bases are same as in DNA but the fourth one is uracil (U). A unit formed by the attachment of a base to ¢ position of sugar is known as nucleoside .
In nucleosides, the sugar carbons are numbered as ¢ , ¢ , ¢, etc. in order to distinguish these from the bases (Fig. .5a). When nucleoside is linked to phosphoric acid at ¢ -position of sugar moiety, we get a nucleotide (Fig.
Structure of Nucleic Acids Fig. . : Structure of (a) a nucleoside and (b) a nucleotide Nucleotides are joined together by phosphodiester linkage between ¢ and ¢ carbon atoms of the pentose sugar. The formation of a typical dinucleotide is shown in Fig.
. . A simplified version of