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In 1928, Frederick Griffith published his work with two strains of Streptococcus pneumoniae and their abilities to infect and kill mice. He noted differences between an encapsulated S strain that appeared "smooth" when grown on agar plates and a non-encapsulated R strain that appeared "rough" by comparison when grown on agar plates. The S strain was pathogenic due to the production of an extracellular capsule while the R strain was unable to produce this capsule and was therefore not pathogenic. Using various combinations of living and heat-killed (dead) R and S strains, he demonstrated the process of transformation and proposed the existence of a transforming principle.

After Griffith’s experiments, three researchers (Avery, McCarty, and MacLeod) did experiments in 1944 to determine what macromolecule was responsible for transformation by adding protease (an enzyme that degrades proteins) and DNAse (an enzyme that degrades DNA) to various combinations of the S and R strains.

Suppose that their experiments had the results shown below. Put yourself in the shoes of the researchers at the time and use these data to infer which experiment tells us something about the nature of the genetic material.

Experiment W: Infection with Live S + Dead R + protease: mouse DIES
Experiment X: Infection with Live S + Dead R + DNAse: mouse DIES
Experiment Y: Infection with Live R + Dead S + protease: mouse LIVES
Experiment Z: Infection with Live R + Dead S + DNAse: mouse DIES

Based upon the data presented here, which experiment demonstrates the nature of the macromolecule responsible for heredity?

A

Experiment W demonstrates that the macromolecule responsible for heredity is protein in nature.

B

Experiment X demonstrates that the macromolecule responsible for heredity is DNA in nature.

C

Experiment Y demonstrates that the macromolecule responsible for heredity is protein in nature.

D

Experiment Z demonstrates that the macromolecule responsible for heredity is DNA in nature.

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