Question

A) A scientist cultures E. coli in the presence of a radioactive phosphate source. After growing the culture for 2 hours, she grinds up the E. coli and separates the bacterial DNA from the proteins. Which sample will contain most of the radioactivity and why?

B) The experiment is repeated, but this time, the bacteria are grown in the presence of radioactive sulfate instead of phosphate. Which sample will contain the radioactivity and why?

Answer 1

Step-by-step explanation:

A. The bacteria DNA will contain most of the radioactivity. The reason is that the DNA is made up of a sugar phosphate backbone which forms its structural framework. One grinding up the bacteria, the radioactive phosphate will likely react with the DNA.

B. In the second instance, the proteins will contain the radioactivity this is because, the DNA does not have any reaction with sulphur, on the other hand, proteins contain about 3 - 6% sulphur.