The cell cycle is the sequence of events that a cell undergoes in order to replicate its DNA and divide its cytoplasm. It consists of four distinct phases known as interphase, prophase, metaphase, and anaphase. Of the four phases, interphase— the longest phase of the cell cycle— constitutes the majority of the cell cycle and is generally divided into three sub-phases: G1, S, and G2.
Interphase is when the cell engages in activities such as carrying out metabolic processes, synthesizing proteins, and growing in size. During interphase, the cell actively prepares for the cell division process. During G1, the cell synthesizes several proteins and organelles and diversifies its gene expression. During S, the cell replicates its DNA— each chromosome duplicates itself in preparation for nuclear division. During G2, the cell finalizes its preparations for mitosis by synthesizing additional proteins.
Importantly, interphase is the longest phase of the cell cycle, typically lasting anywhere from 5-15 hours depending on the species. During interphase, the cell continues to grow, allowing for its eventual division into two daughter cells. This growth can be attributed to G1, as the cell increases in size and increases its enzymatic efficiency.
At the end of interphase, a messenger molecule signals the start of the next phase of the cell cycle: prophase. During prophase, the genetic material condenses and the nucleolus, a structure found in the nucleus of the cell, dissipates. Chromosomes become visible due to the condensation of the genetic material, and spindle fibers form to separate the duplicated chromosomes. During metaphase, the chromosomes are aligned in the center of the cell, and the spindle fibers are used to pull the chromosomes apart.
Next comes anaphase, when the spindle fibers separate the chromosomes and pull them to opposite sides of the cell. This marks the start of the second longest phase of the cell cycle, cytokinesis. During cytokinesis, the two sides of the cell separate, forming two daughter cells. Finally, telophase marks the end of the cell cycle, when the two daughter cells undergo the steps of interphase to begin the cycle anew.
The length of the cell cycle— from the start of interphase to the end of telophase— typically takes from 12-24 hours depending on the cell type. Across the board, however, interphase is the longest phase of the cell cycle, and it plays a critical role in the successful replication of a cell’s genetic material. Without the necessary time allotted for interphase to fully prepare the cell for cell division, the entire cell cycle can be disrupted, leading to apoptosis, or cellular death. Interphase, in other words, is essential for the successful functioning of the cell cycle.