3H thymidine is incorporated into DNA during synthesis. A culture of rapidly gro

Question

3H thymidine is incorporated into DNA during synthesis. A culture of rapidly growing asynchronous cells is given 3H thymidine. The cells are then allowed to grow for 1 hour. At the end of the hour, a sample of the culture is fixed and examined by autoradiography. For the purposes of this experiment, consider that the length of G1 is 15 hours, S is 2 hours, G2 is 3 hours, and M is a half hour. Which result would you predict?

a. All of the cells that are in mitosis, but no others, have incorporated the labeled thymidine.

b. All of the cells, both mitotic and nonmitotic , have incorporated the labeled thymidine.

c . None of the mitotic cells, but some of the non-mitotic cells, have incorporated the labeled thymidine.

d. All of the non mitotic cells have incorporated the labeled thymidine

e. None of the non-mitotic cells have incorporated the labeled thymidine.

Explain why,

Explanation / Answer

The synthesis of DNA occurs during S phase of cell cycle. The cells incubated with 3HThymidine for one hour may result in incoporation of radioactive thymidine into cells of S phase or nomitotic phase. Several nonmitotic cells (almost 1/3rd of cells) can be detected with radioactive thymidine and also the mitotic cells. This is due to the cells in synthesis phase are readily detected and cells in mitotic phase are also detected because, the cells in synthesis phase may enter mitotic phase within 30 minutes or half an hour. The cells ae incubated for 1 hour. Therefore, option b is correct.

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