Interphase refers to the portion of the cell cycle that occurs between two cell divisions. During this phase, the cell performs its normal functions and prepares for the next mitosis. Proper cell cycle progression is monitored at two interphase checkpoints and at one checkpoint during mitosis.
What is interphase?
Interphase refers to the portion of the cell cycle that occurs between two cell divisions. Interphase is a part of the cell cycle that consists of mitosis and the phase between cell divisions. In over 90 percent of the time of the cell cycle, the cell spends in interphase. Both interphase and mitosis are again divided into different sections. The cell cycle is a recurrent cyclic process, which is divided into cell growth and cell division. To avoid disturbances in cell proliferation, several control mechanisms are built into this process. Cell proliferation and cell growth must be in balance. In embryogenesis and the physical growth phases, mitosis predominates within the cell cycle. The interphase is divided into three stages. These are the phases G1, GS and G2. The letter G stands for the English word ‘gap’. Depending on the cell type, phase G1 can also be followed by a longer resting phase, which is called G0.
Function and task
After a cell division (mitosis), there is always a phase that prepares the next cell division. This is the interphase. The function of the body is always dependent on the formation of new cells and the death of old cells. In the course of life, a constant process of renewal and regeneration takes place. Even in the old age of an organism, the cell cycle still functions, although by then cell division slows down more and more. During mitosis, two new cells with identical genetic material are formed from one cell. The genetic material is present as DNA in the chromosomes. The chromosomes in turn consist of one or two chromatids. A chromatid is composed of a DNA double strand and chromatin proteins. In the G1 stage of interphase, the chromosomes each contain only one chromatid, because during mitosis the two identical chromatids of the chromosome were separated and divided between the two new cells respectively. In this process, the G1 stage of interphase is mainly characterized by cell growth and the formation of new cell organelles. Furthermore, protein biosynthesis and RNA synthesis take place. At this stage, the cell reaches its typical nucleus-to-plasma ratio. When this ratio is exceeded, the cell can no longer perform its specific function at this stage. The cell enters the GS or G0 stage. During the GS stage (S for synthesis), the cell is still in the cell cycle and synthesizes new DNA to replicate identical chromatids. An identical copy is made for each chromatid. They are joined together within the chromosome via the centromere. Thus, the chromosome now consists of two chromatids. The centrosomes also duplicate. This creates the basis for the next cell division. However, the G1 stage can also be followed by a G0 stage. During the G0 stage, the cell is in a reversible resting phase in which it is not prepared for the next mitosis. Depending on the cell type, the cell then performs important functions for the organism. The resting phase can vary in length. For example, nerve cells usually do not divide again and stem cells can also remain in this stage for a very long time. However, if the cell is already in the GS stage, the next cell division will take place soon. The GS stage is followed by the G2 stage of interphase. In this stage, protein and RNA synthesis continues in preparation for the next mitosis. At the same time, checks are made to ensure that chromatid replication has proceeded without error. In total, interphase lasts approximately 23 hours with about 10 hours for phase G1, 9 hours for phase GS, and 4 hours for phase G2. The subsequent mitosis is completed within only about 40 minutes. Thus, a complete cell cycle takes about 24 hours. However, if the interphase is interrupted by resting phases, this results in quite different times for the overall process. This varies from cell type to cell type.
Diseases and ailments
Disruptions in the cell cycle process can have devastating health consequences.Both in the growth phase and in stable life phases, the correct ratio of cell renewal and the death of old cells is always important. If this ratio is disturbed, malignant tumors can develop. Cancer is always characterized by uncontrolled cell growth. Within the tumor, the regulatory mechanism that stops ongoing cell division fails. The causes are manifold. However, there are three control points in the cell cycle, which control the proper course of processes and at the same time take care of the correct distribution of chromosomes. Thus, there are two control systems within the interphase and one control system within the cell division phase. Within mitosis, a check takes place at the metaphase checkpoint as to whether all chromosomes are attached to the spindle. In interphase, there is the G1 checkpoint and the G2 checkpoint. Here, a check is made in each case to see if the environmental conditions are favorable for cell division. At the G2 checkpoint, it is still checked whether the chromosomes have two chromatids. By means of a complex of cyclin-dependent kinase and cyclin, cell division is then regulated.
