• G1 Phase: growth phase.
During the G1 phase, cell development is subject to the influence of stress and various environmental and metabolic components. In this phase, the cells synthesize many proteins, amplify organelles including ribosomes and mitochondria, and grow in size.
• S phase: DNA synthesis.In this phase, each chromosome consists of two sister chromatids following replication to double the amount of DNA.
• G2 Phase: after passing S phase, the cell enters G2 phase. During this phase, the main task of the cell is to prepare for mitosis. this phase is marked by significant protein/lipid synthesis and cell growth. During and after DNA replication, DNA double-strand breaks accumulate in the cell and must be repaired before the cell can pass the G2/M checkpoint.
• M phase: mitosis and cytokinesis which are tightly coupled.
The M phase includes mitosis, during which the nucleus of the cell divides, and cytokinesis, in which the cytoplasm of the cell divides to form two daughter cells. Segregation of chromosomes and cytoplasm must be tightly coordinated to generate offspring with the correct complement of chromosomes.
Mitosis is divided into prophase, prometaphase, metaphase, anaphase, and telophase (1)
After the M phase, the cells enter the G0 resting stage, which means that the cells lose the ability to further divide for a period of time (4)
The perfectly controlled cell division of mammalian cells is essential for cell homeostasis and development. The transition through the different stages is tightly controlled by the cyclins (cyc), their partners Serine/Threonine cyclin-dependent kinases (CDKs), the CDK inhibitors (CKI) and the retinoblastoma family of proteins (pRb) (2,3).