We explain what the cell cycle is, its phases, control and regulation points. In addition, its implication in the development of cancer.
What is the cell cycle?
The cell cycle is the orderly and sequential set of events that take place within all cells in general. They involve their growth and eventual reproduction in two “daughter” cells . This process is essential for the existence of multicellular beings .
It begins with the appearance of a young cell and culminates with its maturation and cell division , that is, the creation of two new cells. It is performed according to a set of stimuli and biochemical responses interpreted by the cell nucleus , which guarantee the orderly reproduction of body tissues.
Therefore, cells normally start their cell cycle when environmental conditions are conducive to this. However, the cycle does not always occur in the same way, with important animal and plant or prokaryotic and eukaryotic cell variations . However, it occurs in all living beings , with similar purposes and similar stages.
Phases of the cell cycle
The stages of the cell cycle are described according to the formula:
- G 1 : from English Gap 1 or Interval 1
- S : Synthesis or Synthesis
- G 2 : Gap 2 or Interval 2
- M : M-phase or Phase M, whose name is due to the fact that it includes mitosis or meiosis , before cytoplasmic division or cytokinesis.
The cells, before undertaking the cell cycle, are called “quiescent” (meaning that they choose to be still), and once they have undertaken the cell cycle, they are called “proliferating” (meaning that they multiply rapidly).
The cell cycle is not linear, but circular, since young cells can choose to repeat the process, thus creating two new ones each, as dictated by the needs. And broadly speaking, the different stages that comprise it are organized based on two separate phases, which are:
Interface . This first phase includes the G1-S-G2 stages, and during them it grows to its proper level to initiate the duplication of its genetic material, copying it completely according to its DNA .
- Gap stage 1 . The cell grows physically, doubling its organelles and the proteins necessary for the following stages.
- Step S . A complete copy of the cell’s DNA is synthesized, as well as a duplicate of the centrosome, which will help separate the DNA at later stages.
- Gap stage 2 . The cell grows even more in size, generates new proteins and organelles and prepares for mitosis, cell division.
M phase . The mitotic phase begins when the cell has already doubled its genetic material and organelles, ready to divide into two identical individuals. The onset of mitosis starts from the separation of DNA into two double chains, and the two new cell nuclei move away from each other, towards opposite poles.
Phase M is divided into four distinct phases: prophase, metaphase, anaphase, telophase .
Thus, when cytokinesis begins, which is the preparation for the definitive separation of the two new cells, each nucleus is separated. It begins to generate a barrier between both cells, which will then be part of the plasma membrane itself , and finally physical separation occurs.
Cell cycle regulation
The cell cycle must occur under very specific conditions , which merit very specific instances of control and regulation. So without the precise instructions, not only does the entire cycle not start, but transit from one stage to the next will not occur.
In the first instance, control is exercised by genes in the cell’s own genetic code . There are instructions to manufacture or modify proteins to detonate each stage of the cycle. The set of enzymes that activate, facilitate or end each phase are cyclin and cyclin- dependent kinases .
Cell cycle control points
There are, especially during mitosis, a series of cell cycle control points, in which the process is monitored and ensures that no mistakes have been made. These are transitory existence verification routes , that is, once their function has been fulfilled and it has been verified that the process continues without failures, they disappear.
In addition, if the problem, after a period of time, has not been satisfactorily resolved, these control points prepare the cell to undertake self-destruction or apoptosis .
The control points during mitosis are:
- At the end of the G1 stage and before the S . This is the control point for the non-replicated DNA, which inhibits the Cdc25 gene, which in turn activates Cyclin A / B Cdk1. Thus, it prevents the cycle from continuing.
- Before anaphase in mitosis . It is a control point that guarantees the separation of chromosomes , and operates by activating the Mad2 protein that prevents the degradation of segurin, until the conditions are appropriate.
- DNA damage control points in G1, S or G2 . In the event that cellular damage occurs, specifically to the genetic material, the p53 protein will be activated, which allows DNA repair. In case this fails, the apoptosis processes are immediately activated.
Importance of the cell cycle
The cell cycle is the fundamental cycle of cell reproduction, which allows the growth of multicellular organisms and tissue repair . In addition, it causes the necessary proliferation to, for example, generate the critical cell mass to form embryos of future new individuals of the species.
It is a process that is carried out constantly . It is encoded in our DNA itself, so it is one of the fundamental and original cycles of eukaryotic cell life.
Cancer and the cell cycle
As is known, cancer is a disease in which certain cells of certain tissues initiate an abnormal , unstoppable reproduction of dysfunctional cells. This process, which may well cause death if it is not stopped in time, is not interrupted by the natural process of cellular apoptosis , so it requires medical intervention.
Many specialists suggest that the beginning of the carcinogenic process is in certain regulatory genes of the cell cycle that do not work well or were damaged, subjecting the process to a lack of control that in turn engenders other failures and culminates in the formation of a tumor. These genes are known as oncogenes, and their precursors as protoncogenes.