Question

Suppose you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added. What would happen if a cell replicates once in the presence of this radioactive base? a. One of the daughter cells, but not the other, would have radioactive DNA. b. Neither of the two daughter cells would be radioactive. c. All four bases of the DNA would be radioactive. d. DNA in both daughter cells would be radioactive.

Answer 1

In the presence of radioactive thymine, both daughter cells would end up having radioactive DNA after one replication cycle, indicating the semiconservative nature of DNA replication.

Step-by-step explanation:

If you are provided with an actively dividing culture of E. coli bacteria to which radioactive thymine has been added, and a cell replicates once in the presence of this radioactive base, DNA in both daughter cells would be radioactive. This scenario is similar to the classic experiments conducted by Meselson and Stahl, who used isotopes to study DNA replication. The radioactive thymine would be incorporated into the newly synthesized DNA strands during replication, leading to both daughter cells containing this marker, confirming the semiconservative nature of DNA replication.

Answer 2

D. DNA in both daughter cells would be radioactive.

Step-by-step explanation:

DNA replication is a semiconservative process in which each parental strand serves as a template for the synthesis of a new complementary daughter strand. The central enzyme involved is DNA polymerase, which catalyzes the joining of deoxyribonucleoside 5′-triphosphates (dNTPs) to form the growing DNA chain.