Topic 26: The Cell Cycle and Cancer

Question 1

Describe the three checkpoints that regulate the cell cycle.

Answer 1

The three checkpoints
- G1 Checkpoint: The G1 checkpoint is regulated both internally and externally.
It regulated internally by checking the cell size, DNA, and for adequate reserve to move on.
It is regulated externally by waiting for an external signal that gives the cell the yes to move on to the next-stage allowing it to move through every phase.
If it does not receive the signal it will move the cell into a G0 phase (resting phase).
- G2 Checkpoint: The G2 checkpoint is right before the mitotic stage. It checks that the new DNA replicated is correct, cell size, and that it has the right amount of reserve to move on to the next stage.
- M Checkpoint: The M checkpoint is on the mitotic stage, specifically on the metaphase phase. Here it checks if all the kinetochores is attached to a mitotic spindle to move on to Anaphase.

Question 2

Describe how the cells become cancerous.

Answer 2

Cells become cancerous when a mutation occurs in the cell cycle and oncogenes are on and tumor suppressors are turned off.
Cells continue dividing uncontrollably until cancer is formed.

Question 3

Compare proto-oncogenes and tumor-suppressor genes. Give examples of each.

Answer 3

Proto-oncogenes are genes that promote cell growth, important for cell division.
Oncogenes promote cell growth on mutated cells.
Tumor Suppressor inhibit cell growth. They are great for stopping damaged cells from dividing, but when turned they can’t do much.