The longest stage of the cell cycle is the interphase. The interphase is the period between two successive cell divisions and includes the G1, S, and G2 phases. The G1 phase is the longest phase of the cell cycle and is characterized by cell growth and preparation for DNA synthesis. The S phase is the phase during which DNA replication occurs, and the G2 phase is the phase during which the cell prepares for mitosis or meiosis.