what are nucleotides and nucleosides?

Nucleotides are molecules when joined together make up the structural unit of DNA or RNA.

 A Nucleotide consist of three parts : 

• Sugar: The sugar has 5 carbon atoms, therefore it is called a pentose. It can be ribose or 2'-deoxyribose sugar.
• Nucleobase or nitrogenous base (Purines and pyrimidines)
•  One Phosphate group

 Examples are Deoxyadenosine monophosphates(dAMP), Deoxyguanosine monophosphates (dGMP), etc

Nucleosides lack phoshate group or they can be called as nucleotides lacking phosphate group. Examples are  Deoxyadenosine, Adenosine, Guanosine, Uridine, Thymidine etc.