Tuesday, March 1, 2011
RNA molecules have various functions in the cell. Many of the functions are associated with translation, in which the genetic code of messenger RNA molecules is used to help the ribosomes synthesize a specific protein. In addition, ribosomal RNA is the main component of the ribosome, and transfer RNA does the actual translating from nucleotide sequence into amino acid sequence.
RNA molecules may also function as enzymes. They do so either alone or in association with proteins. RNA molecules associate with proteins, for example, when they serve as components of machinery that helps make other, newly formed RNA molecules functional.
RNA is chemically better suited to carry out certain tasks than is DNA. There are also other reasons RNA, not DNA, is used for these tasks. First, it is desirable to keep DNA available for replication and not tied up with other functions. Second, the small number of DNA molecules in the cell is often insufficient. Creating many identical RNA molecules that are copies of a single segment of DNA provides the necessary numbers. Third, RNA can be differentially degraded when it is no longer needed, providing an important regulatory mechanism that would be unavailable if there were only one type of nucleic acid.