Interphase is the period of the cell's life cycle between the end of the previous division and the beginning of the next. From a reproductive point of view, such a time can be called a preparatory stage, and from a biofunctional point of view - a vegetative one. During the interphase period, the cell grows, completes the structures lost during division, and then metabolically rearranges itself to move to mitosis or meiosis, if any reasons (for example, tissue differentiation) do not take it out of the life cycle.
Since interphase is an intermediate state between two meiotic or mitotic divisions, it is otherwise called interkinesis. However, the second version of the term can only be used in relation to cells that have not lost the ability to divide.
General characteristics
Interphase is the longest part of the cell cycle. The exception is stronglyshortened interkinesis between the first and second divisions of meiosis. A notable feature of this stage is also the fact that chromosome duplication does not occur here, as in the interphase of mitosis. This feature is associated with the need to reduce the diploid set of chromosomes to haploid. In some cases, intermeiotic interkinesis may be completely absent.
Interphase stages
Interphase is a generalized name for three successive periods:
- presynthetic (G1);
- synthetic (S);
- postsynthetic (G2).
In cells that do not drop out of the cycle, the G2 stage directly passes into mitosis and is therefore otherwise called premitotic.
G1 is the stage of interphase, which occurs immediately after division. Therefore, the cell has half the size, as well as about 2 times lower content of RNA and proteins. Throughout the pre-synthetic period, all components are restored to normal.
Due to the accumulation of protein, the cell gradually grows. The necessary organelles are completed and the volume of the cytoplasm increases. At the same time, the percentage of various RNAs increases and DNA precursors (nucleotide triphosphate kinases, etc.) are synthesized. For this reason, blocking the production of messenger RNAs and proteins characteristic of G1 excludes the transition of the cell to the S-period.
At stage G1 there is a sharp increase in enzymes,involved in energy metabolism. The period is also characterized by high biochemical activity of the cell, and the accumulation of structural and functional components is supplemented by the storage of a large number of ATP molecules, which will serve as an energy reserve for the subsequent rearrangement of the chromosome apparatus.
Synthetic Stage
During the S-period of interphase, the key moment necessary for division occurs - DNA replication. In this case, not only genetic molecules are doubled, but also the number of chromosomes. Depending on the time of examination of the cell (at the beginning, in the middle or at the end of the synthetic period), it is possible to detect the amount of DNA from 2 to 4 s.
The S-stage represents the key transitional moment that "decides" whether division will occur. The only exception to this rule is the interphase between meiosis I and II.
In cells that are constantly in a state of interphase, the S-period does not occur. Thus, cells that will not divide again stop at a stage with a special name - G0.
Postsynthetic stage
Period G2 - the final stage of preparation for the division. At this stage, the synthesis of messenger RNA molecules necessary for the passage of mitosis is carried out. One of the key proteins that are produced at this time are tubulins, which serve as building blocks for the formation of the fission spindle.
At the border between postsynthetic stage and mitosis (or meiosis), RNA synthesis is sharply reduced.
What are G0 cells
ForIn some cells, interphase is a permanent state. It is characteristic of some constituents of specialized fabrics.
The state of inability to divide is conditionally designated as the G0 stage, since the G1-period is also considered the phase of preparation for mitosis, although it does not include the associated morphological rearrangements. Thus, G0 cells are considered to have fallen out of the cytological cycle. At the same time, the state of rest can be both permanent and temporary.
The G0 phase most often enters cells that have completed their differentiation and specialized in specific functions. However, in some cases this condition is reversible. So, for example, liver cells in case of damage to the organ can restore the ability to divide and move from the G0 state to the G1 period. This mechanism underlies the regeneration of organisms. In a normal state, most of the liver cells are in the G0 phase.
In some cases, the G0 state is irreversible and persists until cytological death. This is typical, for example, for keratinizing cells of the epidermis or cardiomyocytes.
Sometimes, on the contrary, the transition to the G0-period does not mean the loss of the ability to divide, but only provides for a systematic suspension. This group includes cambial cells (for example, stem cells).
