Describe nucleotides.
Nucleotides are the basic unit of nucleic acids. It has three components which are chemically distinct :

(1) Nitrogen containing ring organic compound or heterocyclic compound. It can be adenine, guanine, cytosine, thymine (in DNA), uracil (in RNA). 

(2) A pentose sugar. The pentose sugar is ribose in case of RNA and 2' deoxyribose in case of DNA. 

(3) A molecule of phosphoric acid.