Nucleic Acids
Nucleic Acids
Nucleic acids are a group of organic compounds that carry genetic information. Nucleic acids are essential to life since they contain not only a cell's genetic information, but also instructions for carrying out cellular processes. Deoxyribonucleic acid (DNA) is the particular type of nucleic acid out of which genes are made, and genes are the bearers of hereditary traits from parents to offspring.
Nucleic acid was discovered in 1869 by the Swiss biochemist Johann Friedrich Miescher (1844–1895), who first found a sticky, clear chemical in the nucleus of cells. He named it nuclein, and although it later became known as nucleic acid, no one had any idea that it was in some way connected to heredity. The name nucleic acid itself indicates that these clear molecules were first found in the cell nucleus and that they have a mildly acidic character. By 1929, scientists had discovered that there were two types of nucleic acids. One of these contained the sugar ribose (and became known as ribonucleic acid or RNA) and the other contained the sugar deoxyribose (and was called deoxyribonucleic acid or DNA). By the 1930s, most geneticists agreed that the gene was crucial to heredity and was made of some sort of complex chemical, but no one thought it was made of nucleic acid because the acid did not seem to have a complicated enough structure to carry genetic information.
By 1950, however, nucleic acid had been established as the key factor in inheritance, yet in the fall of that year when the young American biochemist James Dewey Watson (1928– ), traveled to Europe to study the chemistry of nucleic acids, no one knew how this chain of fairly simple molecules could contain all the information necessary to form a complex organism. In 1951 when Watson met the English biochemist Francis Harry Compton Crick (1916– ) at the Cavendish Laboratory at Cambridge, England, the two began a collaboration with the goal of determining the structure of DNA (which they believed would then explain how DNA actually works).
In March 1953, the team of Watson and Crick announced that they had discovered the "double helix structure" of the DNA molecule and offered to science what was essentially an explanation of the chemical basis of life itself. Their theory was that the nucleic acid DNA was made up of two twisted strands that are held together by base pairs that make up the actual coded instructions. Each DNA base is, therefore, like a letter in the alphabet, and a sequence of bases can be thought of as forming a message. Nucleic acids were found not only to contain genetic information (DNA), but were also able to carry that information from genes in the nucleus to other structures in the cell. Thus, the building of proteins was found to be controlled by the group of nucleic acids known as ribonucleic acid (RNA). Geneticists eventually came to describe RNA according to its function in the cell, messenger RNA (mRNA) and transfer RNA (tRNA). Both types of RNA are essential for a DNA molecule to make a copy of itself (which in turn is how proteins are made). mRNA passes out of the nucleus and carries the message for making a protein. tRNA reads this message and transfers the right amino acid to where they form proteins. Watson and Crick's landmark discovery of the nature and function of nucleic acids provided the foundation for understanding the chemical basis of life.
[See alsoChromosome; DNA; Enzyme; Genetic Engineering; Genetics; RNA ]