What is the Purpose of Mitosis? | Explanation and Review (2024)

Mitosis, coined by German biologist Water Fleming in 1887, is the process of cell division resulting in two identical daughter cells. But, what is the purpose of mitosis? Mitosis plays a crucial role in growth, cell replacement, and asexual reproduction. This blog post explores the stages of mitosis, its significance, and the differences between mitosis and meiosis.

What is Mitosis?

In 1887, the German anatomy biologist, Water Fleming, coined the term mitosis which comes from Greek andtranslates to “wrap thread”(mitos) and “act or process” (osis). This term was based on the warped thread appearance of the chromatin in the cell’s nucleus in the first stages of mitosis. Now, what is mitosis as a process and what is the purpose? Mitosis is the process of cell division by which the nucleus of the cell divides giving rise to two identical daughter cells.

The Purpose of Mitosis in Eurkayotes

Mitosis happens in all eukaryotic cells (plants, animals, and fungi). It is the process of cell renewal and growth in a plant, animal, or fungus. This process continuously occurs throughout our bodies, even while you are reading this. Cells continuously die in the process of apoptosis (programmed cell death). For you to stay alive and fully functional, these cells need to be continuously replaced. Mitosis is crucial to this process and it is the reason we can grow, heal wounds, and replace damaged cells.

Mitosis is also important in organisms that reproduce asexually. This is the only way that these cells can reproduce. This is the key process that sustains populations of asexual organisms. Mitosis allows for some organisms to maintain alternating life stages (asexual and sexual, such as fungi).

The key to mitosis occurring is the presence of a nucleus. Therefore, organisms without nuclei (prokaryotes) miss out on this impressive process.

Before Mitosis

Before mitosis begins, the chromosomes in the nucleus of the cell undergo replication. The main purpose of mitosis is to produce two daughter cells identical to the parent cell; so the number of chromosomes in the parent and daughter cells must be the same. Mitosis produces two diploid cells from one diploid cell. Thus, chromosome numbers must double before mitosis occurs. Keep in mind that diploid refers to the number of chromosomes in a cell. Haploid cells have one set of chromosomes (n), whereas diploid cells have two sets of chromosomes (2n).

Overview of Mitosis

During mitosis, all chromosomes separate into chromatids (the two halves of a chromosome). These chromatids separate in space, forming the chromatic makeup of each daughter cell. The parent cell has double the number of diploid chromosomes (2 X 2n = 4n). When these chromosomes split into chromatids and divide into two groups, each group has the same number of chromatids and chromosomes as the parent cell. The composition of these chromosomes will also be identical. Once the chromosomes separate in space, cell division occurs to produce two daughter cells. Thus, mitosis uses chromosome replication to produce two identical diploid daughter cells, which are genetically identical to the diploid parent cell. This way all your cells have identical DNA composition.

The Process of Mitosis

The process of mitosis can be mind-boggling to grasp fully; here we will try to work through it systematically. First off, mitosis consists of 5 phases: Prophase, prometaphase, metaphase, anaphase, and telophase. Some textbooks vary in the number of phases. In some instances, they do away with prometaphase and just keep the four fundamental phases.

What exactly happens in each phase of mitosis in animals may differ from what happens in plants. Nonetheless, all cells undergoing mitosis will in one way or another undergo each of the above-mentioned phases.

The Vocabulary of Mitosis

You will need to familiarize yourself with the following terms to fully understand the phases of mitosis explained below:

Cell furrow/cleavage furrow: The indentation found in the cell membrane of a recently divided animal cell.

Cell plate: The synthesized division of a plant cell laid across the metaphase plate. This later forms the middle lamella.

Centriole: An organelle associated with spindle fiber production, located in the centrosome. These are only found in animal cells.

Centrosome: The part of the cytoplasm which contains the centrioles.

Microtubules: Hollow protein tubes that form spindle fibers (among other things).

Tubulin: The protein which makes up microtubules.

Kinetochore microtubules: The microtubules that attach the centrosome to the kinetochore.

Centromere: The point of constriction of a chromosome.

Cohesin: The protein which binds two sister chromatids.

Cytokinesis: Division of the cytoplasm into two equal parts.

Equatorial plane/metaphase plate: The midline of the cell along which chromosomes align during metaphase.

Interphase: The period between mitosis occurrences; the period between one telophase and the next prophase.

Middle lamella: The cell structure between adjacent plant cell walls.

Nuclear envelope: The double membrane that encloses the nucleus.

Nucleolus: The center of rRNA production within the nucleus.

Sister chromatids: The two identical chromatids which form a chromosome.

Spindle fibers: Abundle of microtubules running from one pole of the cell to another, along which chromosomes move.

Now that the definitions are out of the way, let’s dive into the nitty-gritty of this process.

The Phases of Mitosis

1. Prophase

This is the longest phase of mitosis. Numerous important events occur in this phase: the centrioles migrate, the spindle fibers are organized, the nuclear envelope and nucleolus disintegrate, and the chromatin fibers condense (Figure 1).

Prophase in animal cells begins with the migration of two pairs of centrioles from just outside the nucleus, in the centrosome, to the polar ends of the cell. Once at the polar ends of the cell, the centrioles promote the movement of microtubules from the cytoplasm into the spindle fibers. Plant and fungi cells do not have centrioles; therefore, they skip this step.

While this is occurring, the nuclear envelope and nucleolus disintegrate, releasing the chromatin within. The chromatin condenses, and chromosomes become visible. The two chromatids making up each chromosome are identical and are known as sister chromatids. These are held together by cohesin.

Understanding Prophase

Prophase is integral to fulfilling the purpose of mitosis. Think of this phase this way. Every part of the cell that is involved in mitosis changes to prepare for the full mitotic process. For example, at the end of mitosis, the daughter cells need equal amounts of identical DNA. Therefore, there has to be a way of making sure that the right contents go to the right cell. In other words, cells need an insurance mechanism to ensure that one cell does not end up with two copies of one chromosome while the other cell ends up with zero copies. Spindle fibers achieve this by pulling the contents of one daughter cell to the one side while the other “half” is pulled towards the opposite end. This way, chromosomes never get lost and go to the wrong end. In short, things migrate to their rightful corners.

The presence of the nuclear envelope limits how far chromosomes, in particular, can go. So before the cell can consider pulling things apart and duplicating the contents, this barrier needs to be removed somehow. This is why the nuclear envelope disintegrates.

If you follow the logic above it should be obvious why the other events occur.

2. Prometaphase

Prometaphase is an intermediary stage between prophase and metaphase, here the cell is further prepared for metaphase (figure 2).

The spindle fibers attach to the kinetochore of each chromosome, at opposite sides of the centromere. Each sister chromatid is attached to its spindle fibers. These spindle fibers are comprised of kinetochore microtubules. The chromosomes migrate to the equatorial plane (or metaphase plate), which is perpendicular to the spindle fibers.

Here the same logic as above applies; it is all about making sure one chromatid ends up in one cell.

3. Metaphase

Metaphase refers to the alignment of the chromosomes at the equatorial plate following prometaphase.

Each centromere is aligned with the equatorial plate while the chromosome arms extend towards the poles. Each sister chromatid (still joined at this point) is on a different side of the equatorial plate (figure 3).

4. Anaphase

The Anaphase stage is the shortest phase of mitosis.

During this phase, disjunction occurs, and migration of sister chromatids away from each other to the poles of the cell occurs, leading to the formation of daughter chromosomes.

Molecular motors use ATP to shorten the spindle fibers attached to each sister chromatid. In so doing, the chromosomes are split into two genetically identical sister chromatids, known as daughter chromosomes from this point. This event is known as disjunction. As the spindle fibers shorten further, the daughter chromosomes are drawn further apart until grouped at opposite ends of the cell.

There is now a diploid number of chromosomes at each pole.

5. Telophase

Telophase is the final phase of mitosis. After anaphase, two diploid sets of chromosomes are located at each pole of the cell. Cytokinesis then occurs to split the cell into two identical daughter cells.

In animal cells, the cytoplasm is constricted to the point that the cell is divided in two. This results in a cell furrow. In plant cells, a cell plate is laid at the position of the equatorial plane. This later becomes the middle lamella of the plant cell.

Following this, chromosomes are packed to become chromatin, a nucleolus reforms, and a nuclear envelope forms around the chromatin and nucleolus. The spindle fibers disappear, and the cell enters interphase.

Now that we have explored all the different stages go back reread and try to reason each event and its role in fulfilling the purpose of mitosis. This will provide you with the ability to answer any questions about each and every one of these stages.

What is the Purpose of Mitosis?

Mitosis is important for three main reasons: development and growth cell replacement and asexual reproduction.

1. Development and growth

After meiosis has produced a gamete, and this has fused with another gamete to form an embryo, the embryo grows using mitosis. This growth continues throughout an organism’s life, in plants, animals, and fungi. In this way, the original chromosomal set is preserved.

2. Cell replacement

This occurs when the original cell is damaged or wounded. New cells are created to replace those that were damaged. Examples of this are the healing of a cut or a broken bone. When old cells die, new ones replace them to ensure continuing functionality.

3. Asexual reproduction

Single-celled organisms and certain multicellular organisms use mitosis for asexual reproduction. This includes reproduction by fragmentation, as in the case of planaria, and reproduction by budding, as in the case of sea anemones. Many plants reproduce using mitosis.

How is Mitosis Different from Meiosis?

First, we need to understand what meiosis is. Meiosis is the replication of cells that results in each daughter nucleus containing half of the parent cell’s chromosomes. Meiosis is used primarily for the production of gametes, which are incorporated during sexual reproduction. Thus, the main difference between mitosis and meiosis is that mitosis produces somatic (body) cells, which can go on to become part of any bodily tissue, whereas meiosis only produces germ (sex) cells. Organisms that reproduce asexually cannot undergo meiosis, whereas all eukaryotic organisms undergo mitosis.

Mitosis and meiosis are similar in that both can only occur in eukaryotic cells. This is because prokaryotic cells do not contain a nucleus within which to begin the processes of mitosis and meiosis. Instead, prokaryotes replicate themselves using binary fission. Both mitosis and meiosis begin with DNA replication in the parent cell to create four sets of chromosomes: in mitosis, these sets are split to form two diploid daughter cells, while in meiosis, these sets are split to form four haploid daughter cells. This is because cells undergo only one division in mitosis, whereas they undergo two divisions in meiosis.

Summary: Mitosis and Meiosis

The table below summarizes the similarities and differences between mitosis and meiosis.

Conclusion: The Purpose of Mitosis

In conclusion, mitosis is the process of asexual cell replication that is responsible for an organism’s development and growth, including cell replacement, and in certain organisms, asexual reproduction. Mitosis is an integral part of eukaryotic functioning.

Mitosis differs from meiosis in that meiosis is the production of gametes, or sex cells, which will allow for genetic recombination in sexual organisms. However, without mitosis, the embryos formed will never grow to become organisms. Mitosis is preceded by DNA replication, to form two diploid sets of chromosomes.

Mitosis has five phases. The first stage is prophase, where the chromatic material is released from the nucleus, and centromeres migrate to the poles of the cell. Prophase is followed by prometaphase, where the chromosomes migrate to align at the equatorial plane of the cell. The third phase is metaphase, where the chromosomes are fully aligned at the equatorial plane. Metaphase is followed by anaphase, wherein the sister chromatids forming each chromosome are pulled apart to assemble at the poles of the cell; and telophase, where cytokinesis forms two identical daughter cells, genetically identical to the parent cell. Following this, the cell enters interphase, the phase between mitosis events.

Mitosis has given eukaryotic organisms the ability to regenerate cells as necessary without reducing the chromosome set while meiosis has allowed the possibility of genetic recombination. Both are vital for the prevalence and continued survival of eukaryotic organisms.

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