1.Experiments by the following scientists provided critical information concerning DNA. Fully describe 2 of these 3 classical experiments and indicate how each provided evidence for the chemical nature of the gene.
a. Hershey and Chase- bacteriophage replicationThey prepared two separate samples of viruses, one in which the DNA (contains phosphorus but no sulfur) was labeled with a radioactive isotope, 32P, and the other in which the protein (contains some sulfur and no phosphorus) was labeled with a radioactive isotope 35S. E. coli were grown on a medium that contained one of the radioactive isotopes. One colony of bacteria was infected with P-labeled virus, and the other - with S-labeled virus. After infection had begun and the viruses had transferred their genetic material into the bacteria, the mixture was spun in a blender. Thus, two layers were formed: one containing extracellular material and the other - intracellular materialThe results were the following:-the extracellular material contained 35S.
This meant that protein is not inserted in bacterial cells when viruses reproduce-the intracellular material (the infected bacterial cells) contained 32P, which meant that DNA is the carrier of genetic material that is needed for the formation of a viral progeny.
b. Griffith and Avery- bacterial transformationStreptococcus pneumoniae, a bacterium that causes pneumonia, has two forms: virulent (with capsule) and non-virulent (without capsule). Griffith was searching for a vaccine for pneumonia and conducted a series of experiments. One of them (marked in bold) produced a puzzling result.
1) mouse + live encapsulated -> dead2) mouse + heat-killed encapsulated -> alive3) mouse + live nonencapsulated -> alive4) mouse + live nonencapsulated + heat-killed encapsulated -> deadA sample from a dead mouse from experiment n.4 revealed that there were live encapsulated bacteria within the mouse. Griffith concluded that a so-called "transformation factor" could cause a...