A nucleoside is composed of both a nitrogenous base as well as a sugar. Cytosine and adenine are just nitrogenous bases. Guanosine monophosphate (or GMP) is also composed of a phosphate group, which designates it as a nucleotide. The only nucleoside is adenosine.

The pentose phosphate pathway (also known as the hexose monophosphate shunt or HMS), mainly serves to produce for anabolic reduction reactions and ribose-5-phosphate for nucleic acid production.