Question

please help answering

You start with a cell that is grown in normal media. Subsequently DNA is allowed to replicate in an environment with all necessary enzymes, dATP, dCTP, dGTP, and radioactively labeled dTTP (3H thymidine) for 1 cell cycle, (resulting in 2 cells) and then switched back to normal, nonradioactive medium. Cell are allowed to replicate once more, so you end up with 4 cells. How many of these 4 cells with have radioactive dTTP incorporated in their DNA?

Select one:

a. 2

b. 1

c. 0

d. this can not be determined

e. 4

Answer 1

The correct option is​​​​​ a.2

During 1 cell cycle in radioactive medium, the newly synthesized strand of 2 daughter cells will have radioactive dTTP while the strand inherited from the parent will lack radioactive dTTP.

After 1 cell cycle in normal medium, the newly synthesized strand of 2 daughter cells will have radioactive dTTP (inherited as the radioactive strand from the parent) while the other 2 daughter cells will have normal dTTP.