How does S-Cdk help guarantee that replication occurs only once during each cell

Question

How does S-Cdk help guarantee that replication occurs only once during each cell cycle? It blocks the rise of Cdc6 concentrations early in G1. It phosphorylates and inactivates DNA helicase. It phosphorylates the Cdc6 protein, marking it for destruction. It promotes the assembly of a prereplicative complex. Which of the following descriptions is consistent with the behavior of a cell that lacks a protein required for a checkpoint mechanism that operates in G2? The cell would be unable to enter M phase. The cell would be unable to enter G2. The cell would enter M phase under conditions when normal cells would not. The cell would pass through M phase more slowly than normal cells The concentration of mitotic cyclin (M cyclin) rises markedly during M phase. is activated by phosphorylation. falls toward the end of M phase as a result of ubiquitylation and degradation. is highest in G1 phase. Consider two mammalian cells, one in G1 and the other in G0 (stationary) phase. If they are stimulated to pass the restriction point by the addition of an extracellular proliferation signal, but the signal is then immediately removed, what would you expect to happen? Both cells will replicate their DNA. Only the G1 cell will replicate its DNA.

Explanation / Answer

Ans. 25) “C” ( S-Cdk first phosphorylates the Cdc6 and eventually dissociates it from ORC and carry out the ubiquitination and degradation.)

26) “C” (The cell that do not contain protein required for a checkpoint mechanism would enter M phase under conditions when normal cells would not.)

27) “C” (Concentration of mitotic cyclin decreases at the end of M phase.)

28) “B” (G1 cell will only replicate.)

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