Question

Suppose Hershey and Chase found that phage ghosts contained 32P but the label was absent from infected E.coli. Furthermore, suppose they found 35S lacking in the ghost and present in the infected E.coli. They would have concluded?

1) that protein was the genetic material in phage
2) that DNA was the genetic material in phage
3) that somehow the radioactivity prevented DNA from getting into E.coli
4) that protein and DNA together made up the genetic material

Answer 1

Under the hypothetical situation where phage ghosts contained 32P and the label was absent from infected E.coli, with 35S present in E.coli, Hershey and Chase would have concluded that DNA was the genetic material in phage, which is the correct conclusion based on the actual historical experiments.

Step-by-step explanation:

If Hershey and Chase had found that phage ghosts contained radioactive isotope 32P but the label was absent from infected E.coli, and instead found 35S lacking in the ghost and present in the infected E.coli, then they would have concluded that DNA was the genetic material in phage. This is in contrast to the actual historical experiments, where they found the opposite: 32P was detected in the infected bacterial cells and 35S was found in the phage remnants, which led them to their landmark conclusion that DNA, not protein, is the genetic material. The options given are hypothetical and reverse the actual results, so under those hypothetical conditions, the correct conclusion would be option 2) that DNA was the genetic material in phage.

The clarification comes from understanding that 32P labels DNA because phosphorus is a component of DNA and not present in proteins. Conversely, 35S labels proteins since sulfur is found in some amino acids but not in DNA. Therefore, finding 32P in the phage ghosts would indicate that the DNA remained outside the bacterial cells, while finding 35S inside the cells would suggest that the proteins had been transferred inside, which implies that DNA is the carrier of genetic information.

Answer 2

Hershey and Chase's experiment using radioactive isotopes showed that DNA is the genetic material in bacteriophage, supporting the hypothesis suggested by Avery et al. The experiment involved labeling phage particles with 32P, which represented DNA, and then infecting bacterial cells. Only 32P entered the cells, providing evidence that DNA, not protein, was the genetic material. Option 4 is the correct answer.

Step-by-step explanation:

Hershey and Chase conducted an experiment using radioactive isotopes to determine whether protein or DNA was the genetic material in bacteriophage.

They labeled one batch of bacteriophage with radioactive sulfur, 35S, which labels protein, and another batch with radioactive phosphorus, 32P, which labels DNA. After infecting bacterial cells with the labeled phage, they separated the phage particles from the bacterial cells through centrifugation.

The result showed that only 32P, which represents DNA, entered the bacterial cells, indicating that DNA is the genetic material in the phage (option 2). Therefore, Hershey and Chase concluded that DNA, not protein, was the source of the genetic material.