What are nucleotides?

Nucleotide= Sugar + Phosphate group + Any Nitrogen Base

It means a nucleotide is actually the combination of deoxy or oxy ribose sugar; phosphate group attached to 5' end of sugar & nitrogen base like Purines (Adenine, Guanine) ; Pyrimidines (Cytosine, Thymine [For DNA], Uracil [For RNA])

Nucleotides are the subunits that are linked to form the ribonucleic acid (RNA) and deoxyribonucleic acid (DNA), which serve as the cell's storehouse of genetic information.

Free nucleotides play important roles in cell signaling and metabolism , serving as convenient and universal carriers of metabolic energy and high-energy electrons.

All nucleotides are composed of three parts: a five-carbon sugar, a phosphate, and a nitrogen-rich structure called a nitrogenous base. The sugar can be ribose, which is found in ribonucleotides and RNA, or deoxyribose, which is found in deoxyribonucleotides and DNA.

The only difference between these two sugars is that deoxyribose has one fewer oxygen atom than ribose. The five carbon atoms in the sugar are numbered sequentially. To distinguish these carbon atoms from those of the nitrogenous base, which are also numbered, they are designated as 1 (prime), 2 , and so on.

Source:

http://www.biologyreference.com/Mo-Nu/Nucleotides.html