The Scientific Community at this time understood that proteins consisted of combinations of 20 different types of amino acid subunits. DNA, on the other hand, consisted of only four types of nitrogen base subunits. (We now know there are 22 amino acids. The 22nd having been discovered here at OSU!)
2. Considering the wide diversity of life forms, which molecule would the majority of the Scientific Community consider to be the more likely candidate for genetic material, despite Griffith's findings regarding the "transforming factor"?
3. Read through the original papers on Carmen and familiarize yourself with the figures.
INVESTIGATION I: WHAT IS THE NATURE AND STRUCTURE OF THE GENETIC MATERIAL?
Materials (per lab group)
Assorted colored beads representing sugar, phosphate, and nitrogen bases
Procedure
In the 1940s, Oswald Avery noted the following about nuclein:
Nuclein was determined to be DNA (deoxyribonucleic acid), made up of long chains of nucleotide subunits.
The quantity of DNA was equal in all cells of an organism, except for the gametes (sperm and egg cells), which had exactly half the amount of DNA as the other cells.
The amount of DNA in cells of closely related organisms was similar.
DNA was a remarkably stable molecule.
None of these points supported the hypothesis that protein was responsible for heritable traits, but rather supported the hypothesis that DNA played this role.
Avery hypothesized that DNA must be the genetic material. He further investigated Griffith's "transforming factor" and tested his hypothesis through experiments involving careful filtration of chemically digested chromosomes (Figure 8.2). Avery found that Griffith's "transforming factor" was not affected when proteins were chemically digested (destroyed), but was incapacitated when DNA was digested. He concluded that Griffith's "transforming factor" must be DNA.