What are nucleotides ? Describe their structure

Nucleotides are small complex molecules made of:
(1) Njicleotide : Each nucleotide consist of 3 units - a nitrogenous base, a pentose sugar and phosphate group.
(2) Nitrogenous base: Nitrogenous base are the purine (adenine or guanine) or pyrimidine (thymine, cytosine or uracil).
(3) The nucleotides are mono or di or triphosphates of nucleosides, e.g., Adenosine monophosphate (AMP), Adenosine diphosphate (ADP) and Adenosine triphosphate (ATP).