DNA differs from RNA in both structure and function. The two molecules have different types of sugars, vary in the types of nitrogenous bases in each, are found in different places and do different things within the cell.
First of all, DNA and RNA don't have the same sugar in their backbones; DNA contains deoxyribose, which contains one less oxygen atom than ribose, the sugar in RNA. As for nitrogenous bases, DNA contains adenine, guanine, cytosine and thymine; RNA consists of adenine, guanine, cytosine and uracil. The overall structure of the two molecules also differs: DNA has two strands, while RNA only contains one strand.
DNA lives in the nucleus of a cell and cannot traverse the nuclear membrane, whereas RNA enters and exits the nucleus easily. DNA contains the plans for making proteins; however, because it cannot leave the nucleus, an RNA copy is made of the DNA template, and this RNA copy, called messenger RNA, leaves the nucleus.
Several types of RNA perform different functions within the cell. Messenger RNA travels to structures called ribosomes. Within the ribosomes, another type of RNA, transfer RNA, brings the various amino acids that make up proteins to the ribosome. The messenger RNA provides the code so that the transfer RNA can bring the correct amino acid to connect to the growing protein chain. Ribosomal RNA forms part of the structure of the ribosome. DNA, however, consists of only one type.