(a) What are essential and non-essential amino acids ? Give two examples of each. (3 marks)
(b) How are nucleosides different from nucleotides ?
(a) Non-essential amino acids : The amino acids which can be synthesised in the body, are
known as non-essential amino acids.
Example : Glycine, Alanine etc.
Essential amino acids : The amino acids which cannot be synthesised in the body and must
be obtained through diet are known as essential amino acids.
Example : Valine, Leucine etc.
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.