There are an estimated 37.2 trillion cells in the average adult human body. 37.2 trillion is a staggering number, especially when we remember that we all develop from a single fertilized egg cell. So how does one cell become 37.2 trillion cells? Through mitosis.
Mitosis is the process of cell division, in which one cell produces two new daughter cells that are genetically identical to each other. Mitosis occurs during development, creating more cells that allow an organism to grow, but it also takes place throughout the lifetime of an organism, as means to replace old cells with new ones.
Defects during cell division can result in cells containing either too few or too many chromosomes, which are molecules of DNA. Human cells, for instance, have 23 pairs of chromosomes and either the loss or gain of a single chromosome can lead to developmental disorders and certain diseases like cancer. As such, the process of mitosis requires absolute accuracy.
Based on visual observations, mitosis is classically divided into five phases: prophase, prometaphase, metaphase, anaphase and telophase. Interphase is the cell cycle stage in between two cell divisions. This is the cell equivalent of half time during a game, and it allows the cell to grow and double its genetic content in preparation for mitosis.
Duplicated chromosomes are referred to as “sisters,” and they remain closely linked. The linkage is particularly strong at the center of the chromosome within a region known as the centromere, and this is why chromosomes often appear X-shaped. This X-shape becomes visible at the start of mitosis during Prophase, as the chromosomes condense, transitioning from a loose “spaghetti” form into “rods,” which helps prevent them from tangling up as the cell divides.
The primary goal of mitosis is then to line up the duplicated chromosomes in the middle of the cell (Metaphase), and to equally split them apart (Anaphase) so that both daughter cells receive the same number of chromosomes. A spider-like structure called the mitotic spindle supports this process. The spindle consists of microtubules that connect to the chromosomes and, by growing and shrinking, provide the forces required to separate the duplicated chromosomes from each other. While the chromosomes move to opposite poles, the center of the cell contracts during the last phase of mitosis (Telophase), pinching off the two new-born daughter cells.
Leah was even inspired to design mitosis shirts! You can find them in her shop here.
Contributed by Leah Bury, a postdoc at the Whitehead Institute in Cambridge, and our Featured Artist for June, 2018. To meet Leah and see more of her art, click here.
During interphase, it is easy to identify the DNA in the nucleus of a cell, but during mitosis, the DNA must be replicated to make new chromosomes. “Threading a needle” necessitates described replication process is sometimes as that all of the nuclei DNA be condensed into a single point, much like threading a needle. This location, called the metaphase plate, creates new threads.
The metaphase plate moves from underneath the nuclear membrane to opposite cell ends. At the metaphase plate, two daughters create new threads are that will form the cells. If a cell is too small, this stage of mitosis will not occur, and division will either not occur at all, or it will be delayed.
Anaphase is the stage that separates one daughter cell from another: it is also known as telophase or division. At this stage, each daughter cell has half the number of chromosomes as the original parent cell and contains a complete DNA set.
Cytokinesis followed Telophase, which divides the cytoplasm and plasma membranes that form between daughter cells. After cytokinesis, create two new cells. All organelles, along with cytoplasm and membrane, present in the parent cell are divided equally between the two new cells.
During cytokinesis, the nucleus also migrates to the center of each new daughter cell: DNA replication and division have occurred exclusively in the cytoplasm.
Finally, mitosis ends with a process called interphase, and the cell begins to grow and increase its DNA content in preparation for another round of mitosis. The whole process is repeated indefinitely – which means that even a 37.2 trillion cell organism has to keep going through mitosis if it is to survive.
Leah even got the idea to create mitosis shirts. These shirts can be found in Leah’s shop here.