Dna Discovery Essay

The discovery that genetic information was passed on through DNA as well as the physical structure of DNA being a double helix, containing two complementary strands of DNA were some of the most significant biological discoveries in recent history. This particular discovery developed numerous areas of the science due to the fact that based of this discovery, numerous other hypotheses were made including about how DNA was replicated. Despite the fact that the replication process was easy to deduce, proving what hypothesis actually occurs was a challenging task. In 1958 Franklin Stahl and Mathew Messelson used the technique of density gradient centrifugation, to prove that DNA occurs in a semiconservative fashion.
Prior to the experiment, there

This isotope of nitrogen contains one more neutron within its nucleus causing for it to have a higher atomic mass that 14N. Due to the fact that nitrogen atoms construct part of the purine and pyrimidine bases within DNA, the DNA of E. coli was marked using 15N through growing the bacteria within 15N ammonia salts as the sole source of nitrogen. This then allowed for the parental DNA to be labelled, therefore the next step was the marking of the daughter strands. This was accomplished through the newly marking the newly synthesized DNA strands containing 14N through placing the replicating bacteria within 14N ammonia salts. After a period of time separate samples were taken from the culture of bacteria (collecting DNA with just the heavy isotope, DNA with just the light isotope, and DNA containing both) was mixed with cesium chloride solution CsCL2. Through the use of centrifugation at high speeds, the DNA moved to a particular position within the gradient where the DNA matched the density of the solution. Due to the different atomic weights of the isotopes within the different strands of DNA, it caused for the different densities to sediment at different levels. The DNA with only the heavier isotope 15N, was found to be lower than the DNA with only the lighter isotope 14N within the gradient. The DNA that was hybrid containing both the light and heavy isotope was located between the two at an intermediate