Question

Comparing the rate of DNA synthesis with and without cytochalasin B, the researchers hypothesized that the toxin increases the diffusion of thymidine into the embryos. Explain their logic.

Short answer

According to the question, the hypothesis is that toxin (cytochalasin B) increased the diffusion of thymidine into embryos. This is because DNA is labeled more extensively due to a greater uptake of labeled thymidine.

Step-by-step solution

Cytochalasin B 

Cytochalasin B is a toxin that is permeable to the cell membrane. It obstructs the development of contractile microfilaments. Hence, it inhibits cell movement and cytoplasmic division. It is used for cell cycle studies, cell imaging methods, and also as an anticancer drug.

It consists of carbon, hydrogen, nitrogen, and oxygen in its structure. Its molar mass is 49.6 g/mol. It is used for cytological research because it inhibits the network formation by actin filaments.

Diffusion of thymidine into embryos

Radioactively labeled thymidine is a nucleoside that researchers use to determine the rate of DNA synthesis. The increased diffusion of thymidine into embryos indicates that due to greater uptake of labeled thymidine, DNA is more largely labeled. This increases the diffusion rate of thymidine into embryos.

Effect of the toxin on the diffusion of thymidine

The rate of DNA synthesis is the same with and without the toxin. However, the diffusion of thymidine is increased into embryos due to the presence of thymidine. This suggests that uptake of labeled thymidine is more in DNA, which increases its amount during DNA synthesis.