Answer the following questions : (2 marks)
(i) Why are vitamin A and vitamin C essential for us ?
(ii) What is the difference between a nucleoside and a nucleotide ?
(i) Because deficiency of vitamin A and vitamin C causes night blindness and scurvy respectively.
Nucleoside : A nucleoside contains only two basic components of nucleic acids i.e. a pentose sugar and a nitrogenous base. During their formation 1-position of the pyrimidine or 9-position of the purine moitey is linked to of the sugar (ribose or deoxyribose) by a -linkage.
Nucleotides : A nucleotide contains all the three basic components of nucleic acids, i.e. a phosphoric acid group, a pentose sugar and a nitrogenous base. These are formed by esterification of of the sugar of the nucleoside with phosphoric acid.