Question

Q7. Control mechanisms operate both to regulate the onset of each phase of cell cycle and to avoid improper transitions between the cell cycle phases. Important clues to the nature of cell-cycle regulation were established by Rao and Johnson in their 1970 paper in Nature. Rao and Johnson fused mammalian cells that were at different stages of the cell cycle. The resulting 'heterokaryons' possessed two different nuclei — one from each fusing cell — and share the same cytoplasm. In one of their experiment a mammalian cell in G1 was fused with a mammalian cell in S phase. In the fused cell the two nuclei are visible, and it was observed that the fusion caused the G1 nucleus to enter S phase (Rao et al Nature 1970). However, when Rao and Johnson fused a G2 cell with an S phase cell, the G2 nucleus did not undergo DNA replication. Interestingly, again, fusing a cell in mitosis with an S phase cell caused the S phase cell to immediately enter mitosis, but not the mitotic cell entering S phase. a) What can you specifically conclude from the following experiments related to the cell cycle traffic. Can you assume how, or regulating which component the cell manifests such specificity? (Answer in not more than 3-4 Lines). b) Inspired by the story of Rao and Johnson, to study more about cell cycle, you performed some experiments yourself. You exposed yeast cells at G1 phase to growth factors and observed that the cells go into S phase. What do you think would happen if you withdraw the growth factor from the cell culture medium while the cells are in S phase of the cell cycle. (Answer in one to two lines).

Answer 1

Answer:

bsjzifjfncjckcncncjjcjckckvkfjgkgkvkgk