Here's why:

* DNA (Deoxyribonucleic Acid): The "deoxy" in its name refers to the fact that it uses deoxyribose as its sugar. Deoxyribose has one less oxygen atom than ribose.

* RNA (Ribonucleic Acid): RNA uses ribose as its sugar.

The difference in the sugars is one of the key distinctions between DNA and RNA.