Nucleosides

As earlier pointed out, a base combined with a sugar molecule is called a nucleoside. Obviously in DNA four different nucleosides are found. These are (i) deoxycytidine, (ii) deoxythymidine, (iii) deoxyadenosine and (iv) deoxyguanosine. In case of RNA, deoxyribose sugar is replaced by ribose and the base thymine is replaced by uracil. Corresponding nucleosides would be (i) cytidine, (ii) uridine, (iii) adenosine and (iv) guanosine. In a nucleoside, carbon no. 1 in sugar is linked with nitrogen at position no. 3 in pyrirnidines and at position no. 9 in purines.