What is DNA?
The basic unit of all living organisms, from bacteria to humans, is the cell. Contained within the nucleus of these cells is a molecule called deoxyribonucleic acid (or DNA). Today, we
know that DNA is the blueprint used to build an organism – our genetic makeup, or genotype, controls our phenotype (observable characteristics). The directions coded for by our genes controls everything from growth and development to cell specification, neuronal function, and metabolism.
How was DNA discovered?
The Swiss physician Friedrich Miescher discovered DNA in 1868, when he purified a novel substance from the nucleus of white blood cells. This molecule, which he called “nuclein”, had chemical properties unlike any substance previously identified. By the end of the 19th century, scientists had described DNA as a polymer composed of building blocks known as nucleotides. Most scientists believed that DNA was too simple to comprise the genetic material, so biological importance of DNA was not realized until much later.
How did scientists determine that DNA was the genetic material?
In 1928, Frederick Griffith observed that living cultures of a normally non-pathogenic strain of S. pneumonia were able to kill mice, but only after being mixed with a heat-killed pathogenic strain. Because the non-pathogenic strain had been “transformed” into a pathogenic strain, he named this transfer of virulence “transformation”. In 1944, Oswald Avery purified DNA, RNA and protein from the virulent strain of S. pneumonia to determine which was responsible for transformation. Only those recipient cells exposed to DNA became pathogenic, leading to the recognition of DNA as the genetic material. These experiments kicked off a worldwide race to unlock the secrets coded for in our DNA.