The Eukaryotic Cell Cycle and Cancer

Question 1

In a eukaryotic cell cycle, state the importance of the following: G1 checkpoint, S phase and M checkpoint

Answer 1

G1 checkpoint: Checks for DNA damage/mutations, cell size, environmental conditions

S phase: DNA replication prior to division (ensure each daughter cell receives an identical copy of the DNA to the parent cell).

M checkpoint: Ensures spindle fibres have correctly attached to centromeres for even separation of sister chromatids in anaphase.

Question 2

The cell cycle is controlled by both internal and external factors. State one example of an internal factor and one example of an external factor, and explain how each factor can affect the cell cycle.

Answer 2

Internal factor: MPF (made up of the gene products Cdk and cyclin). An increase in MPF is required at the G2 checkpoint for cell to enter mitosis.
External factor: Hormone (e.g. growth factor) binds to complementary receptor on a target cell, which triggers/stimulates cell division.

Question 3

Define cancer.

Answer 3

The uncontrolled division of cells

Question 4

With reference to the checkpoints, explain how preventing the formation of the spindle fibers could inhibit cell division.

Answer 4

Inhibition of the formation of spindle fibers would inhibit mitosis at the M phase checkpoint, as the spindle fibers would not attach to the centromeres. This would stop the cell from dividing.