RNA is an important intermediary in gene expression. Although closely related to DNA, RNA differs in three important ways. In the diagram of RNA structure, we see that the sugar is made up of ribose instead of deoxyribose that is found in DNA. Phosphate groups link the ribose molecules in RNA in the same way that they link the deoxyribose molecules in DNA.
The second important difference is the presence of the nitrogenous base uracil (abbreviated 'U'). Uracil does not exist in DNA. Like DNA, RNA contains cytosine (C), guanine (G), and adenine (A); however, in RNA, uracil (U) takes the place of thymine (T) that exists in DNA. Uracil will act in a similar way to thymine in that it can bind to adenine. The four nitrogenous bases of DNA are A, T, C, and G; while in RNA they are A, U, C, and G.
A third important difference is that RNA is single-stranded while DNA is double-stranded. In the diagram, we can see the single molecule of RNA with its ribose-phosphate backbone and the four nitrogenous bases attached to it.
