Question

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1. Before a cell undergoes mitotic cell division:
   1. what has to happen first, regarding its DNA?
   2. If (what you wrote in 2a) didn’t happen, what problem would arise?

For the list below, indicate which statements are true of the G1, G2, S, or M phase of the cell cycle. A statement may be true of any or all of the phases

f. _______ mitotic cyclin is at its highest level

g. _______ a Cdk protein is present in the cell

h. _______ a cell cycle checkpoint has been identified in this phase

i. ________ nuclear envelope reforms

j. ________ cohesion proteins break down

k. ________ cell is active in doing its “job”

l. _________ cell is getting ready to make proteins needed for cell division

m. __________ S cyclin is at its lowest concentration

Answer 1

a. Before a cell can enter the active phases of mitosis it must go through interphase stage. Because the cell duplicates its DNA during interphase before the cell undergoes mitosis.

b. If a cell does not duplicate its chromosomes, the cell will remain in S phase or undergo programmed cell death.

f. S phase -  mitotic cyclin is at its highest level

The highest level of mitotic cyclin is at its highest level.

g. S-phase - a Cdk protein is present in the cell.

Cdk (Cyclin Dependent Kinases) is an enzyme which activate or inactivate proteins inside the cell. It catalyzes phosphorylation of the proteins present in the cell and initiate DNA replication.

h. G1 - a cell cycle checkpoint has been identified in this phase

Check points are the controlling points in the cell cycle of a eukaryotic organism. At this point the cell cycle is halted for favourable condition to continue next stage.

i. M phase - nuclear envelope reforms

The nuclear envelope reforms around the nucleus in the telophase, the final stage of mitosis.

j. S phase - cohesion proteins break down

Cohesion proteins is called cohesins, present during S phase.

k. G1 - cell is active in doing its “job”

At the end of the G1 phase the cell enter into a resting stage (G0) in order to prepare cell division. At this stage the cell is active and doing its job.

l. S phase - cell is getting ready to make proteins needed for cell division

The cell getting reasy to make various proteins needed for cell division during S phase.

m. G1 - S cyclin is at its lowest concentration

The S cyclin concentration is lowest at G1 phase.