The cells of our organism are in continuous change due to a series of cellular events. These events are known as cell cycle.
Phases of the cell cycle
The cell cycle consists of two phases: the interphase phase and the mitotic phase.
During interphase, the cell grows and performs its functions. In this phase we find three different subphases:
- G1: Subphase in which the cell grows and prepares for DNA replication.
- S: subphase in which the cell replicates its DNA.
- G2: Second phase of growth in which the cell prepares for cell division or mitosis.
- M: phase known as mitosis that gives rise to the two daughter cells.
Phases of mitosis
The mitotic phase also known as mitosis or cell division is the phase during which the cell divides into two daughter cells identical to the original cell. The mitotic phase consists of five main stages:
- Prophase: the nuclear envelope disintegrates and the DNA condenses forming chromosomes. Chromosomes are composed of two identical copies of DNA called sister chromatids, joined by an area called the centromere. At the same time, the mitotic spindle (a complex of microtubules) begins to form.
- Metaphase: the chromosomes line up in the center of the cell forming a structure known as the equatorial plate. The mitotic spindle attaches to the centromeres of the chromosomes and prepares them for the subsequent separation.
- Anaphase: the sister chromatids separate and are pulled to opposite ends of the cell. This process is driven by the microtubules of the mitotic spindle that shorten, pulling the sister chromatids to opposite poles of the cell.
- Telophase: the nuclear envelope appears around each set of chromosomes. The mitotic spindle disintegrates and the cell begins to divide into two daughter cells.
- Cytokinesis: at this stage the cell completes its division by the division of the cell cytoplasm. This process varies between animal and plant cells. In animal cells it occurs by strangulation, while in plant cells a new plant wall is formed in the middle of the cell, completing cell division.
After the cell divides, the two new cells enter to interphase, and the process begins again. The cell cycle is tightly regulated to ensure that the cells divide at the right time and that proper cell division occurs in which the DNA from the parent cell is "passed on" to the two daughter cells.