The pentose sugar in DNA is deoxyribose, and in RNA, the sugar is ribose (Figure 1.1.11.1.1\PageIndex{1}). The difference between the sugars is the presence of the hydroxyl group on the second carbon of the ribose and hydrogen on the second carbon of the deoxyribose (so deoxyribose is "missing" an -OH group). The carbon atoms of the sugar molecule are numbered as 1′, 2′, 3′, 4′, and 5′ (1′ is read as “one prime”).

Note that the two sister chromatids, which are held together by cohesin proteins, are still counted as a single chromosome until they are split apart during mitosis.