The part of the cell cycle that occurs before mitosis can begin is Interphase.

Interphase is a crucial period of cell growth and preparation for cell division. It consists of three distinct phases:

* G1 (Gap 1): The cell grows in size and synthesizes new organelles and proteins.

* S (Synthesis): The cell duplicates its DNA, ensuring each daughter cell receives a complete copy of the genome.

* G2 (Gap 2): The cell continues to grow and prepares for mitosis by synthesizing proteins necessary for cell division.

After completing interphase, the cell enters mitosis, the process of nuclear division.