The Discovery of the Structure of DNA Essay
DNA was first discovered by the Swiss scientist Friedrich Miescher in 1869 when he isolated it (along with RNA) from human white blood cells.Because DNA and RNA were located in the nucleus of the cells, he called the substances “nuclein.” They later became known as “nucleic acids.” At the same time, the search was on for the chemical compound in cells that held an organism’s genetic code.In 1864 Gregor Mendel concluded from his experiments with pea plants that an organism’s characteristics are inherited in discrete “packages” which became known as genes. The question was:where were the genes located in the cell?What chemical substance in the cell held the genetic material?
By 1900, it was known that DNA consisted of 3 types of chemicals:sugars, phosphates, and bases of which there were four types (A, T, C and G). Chromosomes were first seen under the microscope in 1882.Since they doubled just before cell division and halved in number when forming sex cells, it was realised that chromosomes must carry the genes. Chromosomes contain protein as well as DNA and it was assumed that the proteins carried the genes since their molecular structure was much more complex. But a series of experiments by Oswald Avery, Colin MacLeod and Maclyn McCarty showed in 1944 that it was indeed DNA that was the genetic material of the cell. They found that they could transform one type of pneumonia bacteria into another simply by mixing it with the DNA of the other. This result was confirmed by Alfred Hershey and Martha Chase in 1952 while studying how viruses infect bacteria.
Once it was established that DNA did indeed carry inherited information, the race was on to discover how. The key lay in determining the molecular structure and shape of the DNA. In 1949 Erwin Chargoff discovered that the amount of adenine in a sample of DNA was always the same as the amount of thymine, and the amount of cytosine was always the same as the a…