Question

537. There is a defect in one of the proteins that make up the kinetochore such that the kinetochore cannot function. As a result, the mitotic cell cycle is blocked. What stage will the cycle stop at? Explain your reasoning.

538. There is a defect in the DNA Polymerase such that it cannot function. As a result the mitotic cell cycle is blocked. What stage will the cycle stop at? Explain your reasoning.

539. A cell fails to repair DNA damage after synthesis. Will the G2/M cyclin be synthesized? Explain your reasoning.

540. A cell begins to divide even though there are no growth hormones present. What could cause this? Be specific! Explain your reasoning.

541. There is a defect in the G2 cyclin such that it is never degraded. What effect, if any, would this have on the rate at which mutations accumulate as this cell-line continues to divide over many cell cycles? Explain your reasoning.

Answer 1

Ans 537) The cell cycle will be arrested at metaphase stage via spindle assembly checkpoint mechanism and no metaphase to anaphase transition will occur.Tension lacking kinetochores (due to mutation in one of the proteins for kinetochore formation) will be recognized by the CPC (chromosomal passenger complex), and the Chk1 kinase is acivated which inturn activates Aurora B .Aurora B pass the signal to Bub1,BubR1 and Mad2 to inhibit APC (Anaphase promoting complex) to bind to cdc20 (If APC do not bind to cdc20, APC remains inactive).Now,since the APC is inactive,it wont degrade securin and thus separase will not be free to cleave scc1 subunit of cohesin and thus no separation of sister chromatids.This is how metaphase to anaphase transition is blocked by spindle assembly checkpoint mechanism when the kinetochores are not properly attached.