An information-carrying molecule. DNA, as the carrier of the genetic code, is termed a primary semantide and is regarded by taxonomists and evolutionists as a primary source of information in drawing up classifications and evolutionary trees. RNA, as the transcription of the genetic code, is termed a secondary semantide, and proteins as the end product of this information transfer, tertiary semantides. Much effort has recently been directed to unlocking the information carried by such molecules. The amino acid sequences of various proteins, e.g. cytochromes and plastocyanins, have been determined and compared for a number of species. It is now also possible, using restriction enzymes, to determine the base sequences of nucleic acids. See also DNA hybridization. |
