Discovering The Mystery Of DNA

Deoxyribonucleic acid (DNA), is sometimes called the most important chemical on earth, because it makes up our genes. But did you know the tale of its discovery was a long journey, involving many scientists?

Father Mendel and the hunt for the ‘gene’
Father Gregor Mendel, a Catholic monk, carried out experiments in the 19th century which laid the principles of modern genetics. His findings were later confirmed and extended by Hugo de Vries, Carl Correns, Erich von Tschermak and Thomas Hunt Morgan. The most critical finding was that different traits were inherited independently, as if each was a particle (now called a ‘gene’). This set off a hunt to find the chemical nature of the gene.

The chromosome theory
Theodor Boveri was a biologist who showed that chromosomes were necessary for inheritance in sea urchins. Walter Sutton demonstrated this in a grasshopper. Soon evidence mounted that chromosomes were the bearers of heredity, and it was established beyond doubt in 1915.

Chromosomes are very complicated structures in the cell, and contain both proteins and DNA. For a long time, it was a matter of hot debate as to which was the actual carrier of heredity. The debate was finally put to rest in 1944 by Oswald Avery, Colin MacLeod, and Maclyn McCarty, who showed that it was DNA and not protein that caused heredity.

The structure of DNA
A race began to determine the structure of DNA and the chemical basis of how genes work. It was already known that DNA is made of four ‘bases’ – adenine, guanine, thymine and cytosine. In 1950, Erwin Chargaff demonstrated that the total amount of adenine in any DNA molecule equals the total amount of thymine. He showed that the amount of guanine equals that of Cytosine. These are now called Chargaff’s rules.

At the same time Rosalind Franklin, Maurice Wilkins, James Watson and Francis Crick were using a new method for determining chemical structures – X-ray diffraction. Rosalind Franklin carried out many experiments and obtained many X-rays that showed a distinct, repetitive pattern. From this, Crick (who was originally trained as an engineer) deduced that DNA existed in two intertwined strands – called the double helix. The discovery was announced in 1953.

The foundation of a new science
The double helix made it clear how Chargaff’s rules apply. Each strand is a chain made of a combination of the four bases. Every adenine on one strand pairs with a thymine on the other strand, while guanine pairs with cytosine.

Since then, a very large number of advances have been made and a whole science has emerged at the interface of chemistry and genetics. Called molecular biology, it has led to discoveries as to how genes work physically, the basis of genetic disorders and the new fields of gene therapy and genetic engineering.