Question

analyze the graph of cyclin levels. which statement best describes the relationship between mpf and the cell cycle?
cyclin binds with an enzyme to produce mpf cyclin and as its concentration rises, it promotes mitosis. the rise and fall of mpf cyclin controls the cell cycle.
cyclin binds with a factor to produce mpf enzyme and as the enzymes concentration decreases, it promotes mitosis. the concentration of the mpf enzyme controls the cell cycle.
the mpf cyclin concentration remains constant, as the rise and fall of the mpf enzyme controls the cell cycle.
the mpf cyclin concentration rises over time and as it uses up the mpf enzyme after fertilization, it regulates the cell cycle.

Explanation:

To solve this, we recall the role of cyclin and MPF (Maturation - Promoting Factor) in the cell cycle. Cyclin binds with a Cdk (cyclin - dependent kinase, an enzyme) to form MPF. As cyclin concentration rises, MPF activity (which promotes mitosis) increases, and as cyclin concentration falls, MPF activity decreases. The first option correctly states that cyclin binds with an enzyme (Cdk) to produce MPF, and as its (cyclin's) concentration rises, it promotes mitosis, and the rise and fall of MPF (driven by cyclin levels) controls the cell cycle. The second option has incorrect details about the factor and the enzyme's concentration. The third option is wrong as cyclin concentration does not remain constant. The fourth option has incorrect details about using up the MPF enzyme after fertilization (this is not the correct mechanism of cell cycle regulation by MPF and cyclin).

Answer:

A. Cyclin binds with an enzyme to produce MPF Cyclin and as its concentration rises, it promotes mitosis. The rise and fall of MPF Cyclin controls the cell cycle.