Final answer:
A nucleoside composed of cytosine attached to ribose is called cytidine, a molecule formed via an N-glycosyl linkage between the nitrogenous base and the pentose sugar.
Step-by-step explanation:
A nucleoside composed of the base cytosine attached to ribose is called cytidine. Nucleosides are molecules that form when a nitrogenous base is linked to a sugar (pentose) molecule through an N-glycosyl linkage. In the case of cytosine, a pyrimidine base, when it is attached to the 1' carbon of the ribose sugar, the resulting nucleoside is cytidine. This occurs via an N-glycosidic bond. The two categories of nitrogenous bases are purines and pyrimidines, and as a pyrimidine, cytosine forms the nucleoside cytidine when it is connected to ribose.
In RNA, ribose is the sugar present, and thus the nucleotides are ribonucleotides. Specifically, a nucleoside lacks the one or more phosphate groups that, when attached, would make it a nucleotide. The primary structure of RNA consists of a chain of such nucleotides.