Abstract
The cell lifespan starts at the moment that the parental cell divides and completes when the cell undergoes mitosis. The cell cycle is comprised of the sequence of events that take place between two consecutive mitoses and results in the formation of the two daughter cells.
The cell cycle consists of two stages: 1) interphase and 2) M-phase (mitosis) followed by cytokinesis. Interphase represents the period when a cell is metabolically active, grows, transcribes genes, synthesizes proteins, carries out its functions depending on its specialization in a multicellular organism, differentiates, replicates nuclear DNA and prepares itself for a mitotic division.
Interphase is in terms of the cell division divided into three phases: G1 (Gap 1)-, S (Synthesis)-, and G2 (Gap 2)-phase. During the G1-phase, the cell increases the volume of the cytoplasm and synthesizes a range of proteins such as the histones and enzymes required for the replication of DNA.
The S-phase represents the part of the cell cycle in which DNA replication occurs. The G2-phase follows the S-phase, the cell duplicates the organelles and prepares for mitosis.
The M-phase, mitosis, is the final phase of the cell cycle, during which the duplicated chromosomes segregate into the daughter cells. The physical splitting of the dividing cell into the two daughter cells is called cytokinesis.
Progression through the cell cycle, which represents the precise timing of finishing one and entering the next phase, is primarily regulated by two protein families: 1) cyclins and 2) cyclin-dependent kinases (CDKs). Each CDK binds to a different class of cyclins and gives rise to the heterodimeric cyclin-CDK complex with the protein kinase activity necessary for activating the numerous substrates required for progression through the phases of the cell cycle