Interphase

Interphase consists of G1, S, and G2 phases. G1 (gap 1) is when newly generated cells grow and prepare for DNA replication. S (synthesis) is when cells duplicate their nuclear DNA and centrosomes. G2 (gap 2) follows DNA synthesis, with cells continuing to grow and synthesizing proteins and organelles needed for mitosis.

In human cells, the G1 phase spans approximately 11 hours, the S phase takes about 8 hours, and the G2 phase lasts about 4 hours. Together, these three phases comprise interphase, which accounts for roughly 95 percent of the total cell cycle duration of approximately 24 hours.

During the S phase, cells duplicate their nuclear DNA, which remains packaged in semi-condensed chromatin. This replication increases the cell's DNA content from 2n (diploid) to 4n. Cells remain at 4n until cytokinesis, when their DNA content is reduced back to 2n.

During the S phase, cells duplicate the centrosome, a microtubule-organizing structure that forms the mitotic spindle apparatus. The mitotic spindle separates chromosomes during mitosis. This duplication ensures the cell has the necessary structures to proceed through cell division mitosis and cytokinesis.

During G1, cells are metabolically active and continuously grow in size. They copy essential organelles and biochemical molecules, such as proteins, preparing for DNA replication in the subsequent S phase. This phase allows the cell to accumulate the resources needed for successful DNA synthesis.

Throughout interphase, cells grow, replicate their DNA, and synthesize proteins and organelles required for mitosis. By the end of G2, cells have doubled their DNA content, duplicated their centrosomes, and accumulated sufficient energy stores and cellular machinery. The cell is then ready to enter mitosis and complete cell division.

Interphase comprises approximately 95 percent of the eukaryotic cell cycle duration because cells must accomplish multiple critical tasks: growing in size, replicating their entire genome, duplicating organelles, and synthesizing proteins needed for division. These processes require substantial time compared to the relatively brief mitotic phase.