Interphase

Interphase consists of G1, S, and G2 phases. G1 is the first gap phase where cells grow and prepare for DNA duplication. S is the synthesis phase where DNA replication occurs. G2 is the second gap phase where cells continue growing and prepare for mitosis. Together, these phases comprise approximately 95 percent of the cell cycle.

During G1, newly generated daughter cells grow in size and prepare for DNA duplication. Cells are metabolically active, copying essential organelles and biochemical molecules such as proteins. The G1 phase typically spans approximately 11 hours in human cells, during which cells remain diploid with one copy of each chromosome.

During the S phase, cells duplicate their nuclear DNA, which remains packaged as chromatin. This DNA replication increases the cell's DNA content from 2n to 4n. Cells also duplicate the centrosome, a microtubule-organizing structure that forms the mitotic spindle apparatus. The S phase takes approximately 8 hours in human cells.

The centrosome is a microtubule-organizing structure that cells duplicate during the S phase of interphase. It forms the mitotic spindle apparatus, which separates chromosomes during mitosis. By duplicating the centrosome during interphase, cells ensure they have the necessary structures ready for the upcoming mitotic division.

During G2, cells continue to grow and synthesize proteins and organelles required for mitosis. They replenish energy stores and prepare for the first stage of mitosis. The G2 phase typically lasts about 4 hours in human cells. After G2 completion, the cell is ready to enter mitosis.

Interphase takes up approximately 95 percent of the total cell cycle duration. In a typical human cell, the entire cell cycle occurs over approximately 24 hours, with G1 spanning about 11 hours, S phase taking about 8 hours, and G2 lasting about 4 hours. This leaves only about 1 hour for mitosis and cytokinesis.

Following DNA replication in the S phase, cells increase their DNA content to 4n and remain at this level through G2 and mitosis. DNA content is reduced back to 2n only after cytokinesis is complete. Understanding the cell cycle helps clarify how cells prepare for division and maintain proper genetic content.