Each carbon atom in the pentose sugar is assigned a number with a prime sign (').

Ribonucleic acids (RNA) contain ribose, a 5-carbon sugar.

Deoxyribonucleic acids (DNA) contain deoxyribose, which has a hydrogen atom at the 2' carbon rather than a hydroxyl group.

A ribose or deoxyribose sugar with a purine or pyrimidine base attached to the 1' carbon is called a nucleoside.