Cell Cycle Definition and Meaning
What is Cell Cycle?
The cell cycle is the life cycle of a cell. In eukaryotic cells (with defined nucleus), the cell cycle is divided into interface and M phase (mitosis or meiosis and cytokinesis).
In most of the time of the cell cycle, the cell is in the interface, being the preparatory, resting or dormant part. The interface is divided in turn into 3 stages:
- The G 1phase or presynthetic period : where the cell can remain for hours, days or throughout its life,
- The S phase or synthesis period: where the chromosomes replicate, and
- The G phase 2: when duplicate content is prepared for cell division.
On the other hand, phase M is divided into cytokinesis, where the cytoplasm is divided, and mitosis that is summarized in the following phases or processes:
- Prophase: chromosomes condense, the mitotic spindle is created that captures the chromosomes, the nucleolus disappears, and the nuclear envelope breaks down.
- Metaphase: the metaphysical plate is generated.
- Anaphase: the sister chromatids are separated.
- Telephony: mitotic spindle disappears and the nucleolus appears.
A cycle is characterized by not being linear. In this sense, each of the daughter cells has the ability to start the process again.
The cell cycle is important as are the life cycles, since they allow the reproduction and regeneration of the cells that make up all the organs, tissues and elements of living organisms.
Cell cycle phases
The cell cycle of eukaryotic cells is divided into two main phases: the interface and the mitotic phase or M phase.
The interface carries most of the cell’s life. In this phase, the cell lives, grows, and prepares to reproduce. The cell cycle interface is divided into three stages:
- G 1or presynthetic phase : the cell grows, copies the organelles and makes the molecular components that it will need for the later stages.
- Phase S (synthesis): DNA that is in the form of chromatin is replicated and the centrometer is duplicated.
- Phase G 2: The cell grows further, makes more organelles and necessary proteins, and rearranges the duplicate content to prepare for mitosis.
It is important to note that before the cell enters the M phase or mitotic phase, 2 identical and complete copies of the chromosome will be connected, called sister chromatids. Being connected in the centrometer, they are considered 1 chromosome. Then, when separated at the anaphase, each one will be considered a different chromosome.
DNA genetic information is in the form of chromatin before DNA replication. When chromatin condenses, the DNA of eukaryotic cells breaks up into linear pieces called chromosomes. In prokaryotic cells like bacteria, the chromosomes are usually circular.
Mitotic phase (M)
The mitotic phase is the equal distribution of the genetic material that was duplicated at the interface. This is important, since the disorder of the cell cycle can generate diseases, since cells with too many or insufficient chromosomes are usually weak or cause cancer.
The mitotic phase is divided into a mitosis or meiosis and cytokinesis.
The mitosis is the process by which a stem cell divides into two daughter cells. This cell division is asexual, of diploid cells (2n), whose chromosomes come in homologous pairs.
The meiosis , however, is a sexual division of haploid cells, such as, the sperm and eggs, which need to be combined to form a complete set of diploid chromosomes.
The mitotic phase is divided into four sub-stages:
The prophase is subdivided in some texts into early prophase and late prophase or prometaphase.
In early prophase, the chromosomes condense and the mitotic spindle forms that will organize and move the chromosomes. The nucleolus disappears, being the signal of preparation of the nucleus to decompose.
In the methaphase, the mitotic spindle captures and organizes the chromosomes. The chromosomes end their condensation, the nuclear envelope breaks down so that the chromosomes are released, and the mitotic spindle grows to capture more chromosomes.
At metaphase, the mitotic spindle captures all of the chromosomes made up of two sister chromatids and lines them up in the center of the cell creating what is called a metaphysical plate.
Before the next stage of mitosis, the mitotic spindle generates a checkpoint verifying that all the existing chromosomes are in the metaphysical plate and the protein section of the centrometer that links the sister chromatids (kinetochore) are correctly connected to the microtubules of the mitotic spindle. In this way they can be divided evenly.
At anaphase, sister chromatids are separated and pulled towards the opposite poles of the spindle while the chromosome- free microtubules that make up the mitotic spindle grow to lengthen the cell. This process is powered by motor proteins.
In telephase, the mitotic spindle disappears while the nuclear membrane and nucleolus appear.
Meanwhile, the chromosomes are decondensing to make way for the final step of cytokinesis, a process that overlaps with anaphase or telephase.
The cytokinesis is the final stage of cell division, in which the cytoplasm divides to finish form two daughter cells of a stem cell. This process begins in conjunction with anaphase.