What is the difference between DNA and RNA in term of nitrogen bases and pentose sugars?

There are two primary differences between the two molecules in these terms:

• In terms of pentose sugars, the "D" in DNA stands for deoxyribose, and the "R" in RNA stands for ribose. The "deoxy" prefix simply means "without oxygen," indicating deoxyribose is basically the same as ribose, just missing an oxygen. In ribose, the 2' carbon has a hydroxyl group (OH) attached, whereas deoxyribose has only a hydrogen in this position. 


• In terms of the nitrogen bases, which are interchangeable, the DNA molecules use cytosine, guanine, thymine, and adenine (CGTA), whereas RNA uses uracil instead of thymine (CGUA). The uracil still binds with adenine in the same way thymine does. 

Part of the reason for these differences, in terms of evolutionary development, is that they are very similar on the molecular level and therefore easy to create with the same basic cellular machinery, but different enough they can be distinguished from each other when necessary.