DNAi Timeline

Like most things, DNA would not be as well understood as it is today without the contributions from multiple researchers. This post is going to detail the work from some of these contributing scientists that helped develop the current understanding of DNA. A great resource for information on other scientists that contributed work to the evolution of the idea of DNA can be found at this address. This is also the resource that was used for this post.

Martha Chase, Alfred Hershey, and the "Blender Experiment"
In the early 50's, a group of researchers at the Cold Spring Harbor Laboratory were researching bacteriophage genetics (also referred to as phage genetics). Phage are viruses that target, attack, and infect bacteria. At this time, it was already known that phage was constructed with an outer casing of protein that surrounded in inner core of DNA. It was also known that phage relied on bacteria to reproduce, and that phage attached themselves to bacteria by their tails. It was hypothesized that after attaching, the phage pumped genetic material into the bacterial host, causing the bacterial enzymes to be replaced by new phage particles. In 1952, Martha Chase and Alfred Hershey dedicated their work to discovering why the bacteria transformed into a phage producing organism, proving whether or not DNA was a transforming principle. Through chemical analysis, it was discovered that DNA contained high amounts of phosphorus and zero amounts of sulfur. This information was in contrast to the known information about protein, which contains sulfur but no phosphorus. This information was used in an experiment to test which component entered the bacteria for infection. This was designed in a way that radioactive phosphorus (32P) and radioactive sulfur (35P) to selectively label the phage DNA and protein. The radio labeled phage was then combined with unlabeled bacteria so that the phage could attach. The attachment was then disrupted as the culture was mixed in a Waring blender. The samples were then spun in a centrifuge in an attempt to separate the phage from the bacteria. This attempt was successful, and due to the fact that the phage is lighter than the bacteria, it remained suspended in the test tube while the bacteria collected at the bottom in the form of a pellet. After evaluating the sample 35P, it was discovered that the newly produced phage from the bacteria did not contain any radioactive sulfur, unlike the protein coat of the parent phage.  In contrast, the sample 32P contained newly produced phage from the bacteria that was contaminated with radioactive 32P. From this, it was determined that phage DNA was used inside the bacteria to produce new phage, confirming that DNA is the genetic material.

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