Nucleoside contains

The correct option is base-sugar.

To understand the composition of a nucleoside, let us break down the components of nucleic acids (like DNA and RNA):

1. Nitrogenous Base: These are nitrogen-containing molecules that behave as bases. They include purines (adenine and guanine) and pyrimidines (cytosine, thymine, and uracil).
2. Pentose Sugar: This is a five-carbon sugar, which is ribose in RNA and deoxyribose in DNA.

When a nitrogenous base is covalently linked to the 1'-carbon of a pentose sugar through a glycosidic bond, the resulting compound is called a nucleoside. For example, adenosine, guanosine, cytidine, and uridine are nucleosides found in RNA.

If a phosphate group is subsequently attached to the 5'-carbon of the sugar in a nucleoside, it becomes a nucleotide. Therefore, the relationship can be summarized as:
Nucleoside = Nitrogenous Base + Pentose Sugar
Nucleotide = Nucleoside + Phosphate Group (Base + Sugar + Phosphate)

Thus, a nucleoside contains only a base and a sugar.