Figure 13.2
-In an experiment, DNA is allowed to replicate in an environment with all necessary enzymes, dATP, dCTP, dGTP, and radioactively labeled dTTP (3H thymidine). After several minutes, the DNA is switched to nonradioactive medium and is then viewed by electron microscopy and autoradiography. Figure 13.2 represents the results. It shows a replication bubble, and the dots represent radioactive material. Which of the following is the most likely interpretation of the results?
A) There are two replication forks going in opposite directions.
B) Thymidine is being added only where the DNA strands are farthest apart.
C) Thymidine is being added only at the very beginning of replication.
D) Replication proceeds in one direction only.

Question

Figure 13.2
-In an experiment, DNA is allowed to replicate in an environment with all necessary enzymes, dATP, dCTP, dGTP, and radioactively labeled dTTP (3H thymidine). After several minutes, the DNA is switched to nonradioactive medium and is then viewed by electron microscopy and autoradiography. Figure 13.2 represents the results. It shows a replication bubble, and the dots represent radioactive material. Which of the following is the most likely interpretation of the results?
A) There are two replication forks going in opposite directions. 
B) Thymidine is being added only where the DNA strands are farthest apart. 
C) Thymidine is being added only at the very beginning of replication. 
D) Replication proceeds in one direction only.

Quizplus · Accepted Answer

The replication bubble and the dots on both sides of the bubble indicate that there are two replication forks. This means that replication is proceeding bidirectionally, with DNA polymerase synthesizing both strands simultaneously in opposite directions from the replication origin. The radioactive thymidine is incorporated into the newly synthesized DNA strands, which can be visualized by autoradiography.

Figure 13.2 -In an Experiment, DNA Is Allowed to Replicate in an in an Environment