Final answer:
The correct statement regarding the role of Cdk 2 and cyclin E in cell cycle progression is that the amount of free cyclin E is highest during G1. During this phase, cyclin E levels increase, leading to the formation of the cyclin E/Cdk 2 complex which is necessary for the cell to proceed to S phase, thus reducing the amount of free cyclin E before it forms a complex with Cdk 2.
Step-by-step explanation:
In addressing the question of how Cdk 2 (cyclin-dependent kinase 2) forms a complex with cyclin E to enable the progression of the cell from G1 into S phase, and which condition correlates with this mechanism, we note that cyclins regulate the cell cycle by binding to Cdks. The activity of the cyclin E/Cdk 2 complex is essential for the cell to pass the G1 checkpoint and enter the S phase of the cell cycle. The levels of cyclin proteins, including cyclin E, fluctuate throughout the cell cycle, while the levels of Cdk proteins tend to be more stable.
During G1, cyclin E levels increase, leading to the formation of the cyclin E/Cdk 2 complex which is necessary for the cell to proceed to the S phase. Once this transition occurs, the amount of free (unbound) cyclin E would typically be reduced because it is now bound to Cdk 2, and thus, the highest levels of free cyclin E are observed in G1, before it forms a complex with Cdk 2. Conversely, the amount of free Cdk 2 would be expected to decrease as well, because it is becoming bound to the increasing amounts of cyclin E during this phase transition. Therefore, the correct statement is C. the amount of free cyclin E is highest during G1. The activity of the cyclin E/Cdk 2 complex is not highest during G2, as by then, cyclin E has served its purpose in the transition from G1 to S phase and is being degraded.