RNA (ribonucleic acid)
Comparison of RNA and DNA molecules.
RNA (ribonucleic acid) is a class of nucleic acids characterized by the presence of the sugar ribose and the organic base uracil. By contrast, DNA contains deoxyribose and thymine, respectively. Most RNA molecules, including messenger RNA and transfer RNA, act as cellular intermediaries; that is, they convert the genetic information stored in DNA into the proteins that provide cells with structure and enable them to carry out metabolism. In some viruses, RNA also serves as the hereditary material.
Biologists believe that RNA evolved on Earth before DNA. However, a major debate is in progress about the sequence of events leading to the first cellular life-forms, and, in particular, about which came first, RNA or proteins.