Final answer:
Phoebus Levene proposed proteins as the genetic material due to their structural diversity, but later, the Hershey-Chase experiment confirmed DNA, not protein, was the genetic material.
Step-by-step explanation:
Why Did Levene Propose Protein as Genetic Material?
Phoebus Levene proposed that proteins were the genetic material of cells because proteins, with their 20 different amino acids, appeared to offer the vast structural diversity needed to account for the array of genetic traits found in organisms. Levene itself discovered the four nucleotides in DNA; however, he incorrectly believed that the structure of DNA was too simple to carry complex genetic information. Eventually, it was revealed that the genetic material was not protein but DNA, due in large part to the decisive experiments by Martha Chase and Alfred Hershey in 1952. Chase and Hershey provided confirmatory evidence that DNA was the genetic material through their experiments with bacteriophages, viruses that infect bacteria. Proteins were initially thought to be the medium of genetic information due to their complexity and the roles they played in biological processes.
Levene's contributions were initially overshadowed by the misconception that DNA was too simple to be the genetic material. However, later experiments, including those by Avery, McCarty, MacLeod, and particularly by Chase and Hershey, using bacteriophages where radioactive sulfur (35S) labeled proteins and radioactive phosphorus (32P) labeled DNA, unequivocally demonstrated that genetic information is carried by DNA, dismissing the previously held belief that proteins were the hereditary material.