Understanding Cell Cycle: Mitosis And Meiosis

The Process of Cell Cycle and Mitosis

Background

Cell cycle is the process in which a cell prepares to divide and successfully divides into two or four daughter cells. When two daughter cells are produced, mitosis is the process of cell division. On the other hand, when four haploid daughter cells are produces, meiosis is the process of cell division. Mitosis has been found to take place in most of the living organisms including bacteria and plant cells (McIntosh et al., 2016). Mitosis in living organisms is divided into four main phages – Prophase, Metaphase, Anaphase and Telophase. Mitosis also is defined by the production of two nuclei which are identical to the original nucleus. Meiosis, on the other hand results in the formation of four nuclei, which only has half the chromosome content in it.

Mitotic index or MI is a term, which can be stated as the ratio between the total number of mitotic cells and the total number of cells present in the population. Mitotic index is also defined by a specific formula. Mitosis has been found to be divided into a specifically well defined phase (Dominguez-Brauer et al., 2015). Cytokinesis is the final process by which physical division of the cell occurs. This process is preceded by telophase (6^th mitosis stage). Cell division by mitosis has been found to begin with a stage in which chromosomes recruit condensing and undergoes condensation. In metaphase, the chromosomes are compacted and the centromeres of the cells are aligned to the spindle (Maiato et al., 2017). In anaphase, the chromosomes from metaphase plates are associated with the shortening of kinetochore microtubules and thus the shortening process takes place. On the other hand, in the second stage of anaphase, the spindle poles are separated as the non-kinetochore microtubules move apart – or past each other.

During these latter movements, the present thoughts are associated with the function of a motor protein which connect the microtubules with opposite polarity and then start moving towards the end of microtubules. After this process, telophase stage comes and the chromosomes reach each of the poles. On the other hand, the nuclear membrane then starts to decondense into the interphase conformations (Schellhaus, Magistris, Antonin, 2016).  

One example of bacterial cell division is binary fission. This is an asexual reproduction process. In this process, the bacteria carry out a cell division process. This division is same as the mitosis process in which one parent cell divides into two daughter cells. In the process of binary fission, the organism duplicates the genetic material also. DNA is the primary genetic material which is duplicated (Bakhoum et al., 2014). And the cell divides into two major parts known as cytokinesis. Each of the new organisms receives one copy of DNA and finally the two complete daughters are produced.

 

Fig 1: Cell division – Mechanisms in every stage of mitosis

Source: Mcintosh, (2016)

The above figure 1 shows the schematic representation of mitosis. The left figure (A) shows the cell cycle by mitosis. On the other hand, the right figure (B), shows the mechanisms which are followed in every stage of cell division associated with mitosis. The cell cycle has been denoted with G1, S, G2, M, C and repeat. The mechanisms of mitosis associated with the stages (G1 to C) has been shown to be associated with cell division.

Mitotic Index and Calculation

The aim of the experiment is to observe cells undergoing division in a chosen organism. The secondary aim of the experiment is to calculate the mitotic index of the cells undergoing division.

The objectives of the experiment include –

1. To analyse the mitotic stages in mitosis.
2. To differentiate the mitosis stages by a light microscope.
3. To count the number of cells in each mitosis stages in the view of light microscope.
4. To calculate the mitotic index of each stage of mitosis, observed in a light microscope.

 

Fig 2: Mitotic cells observed through light microscope

Source: Laboratory

Total number of cells = 186

Total number of cells in prophase – 162

Total number of cells in metaphase – 9

Total number of cells in anaphase – 5

Total number of cells in telophase – 14

Mitotic indexes –

Prophase = 162/186 = 0.87

Metaphase = 9 /186 = 0.48

Anaphase = 5/186 = 0.026

Telophase = 14/186 = 0.16

The above results shows that most of the cells from the selected view have been found to be in prophase stage. Only few are in telophase and very small numbers are in anaphase and metaphase respectively (Dominguez-Brauer et al., 2015). Thus, it can be concluded that the selected view had cells, which has just begun their cell cycle. The mitotic index was calculated by dividing the total number of cells present in each stage of mitosis by the total number of cells present in the view.

Highest mitotic index was observed for prophase followed by telophase, anaphase and metaphase. Thus, it was concluded that the cell cells were mostly in the initial stages of cell division.

The chromosomes replicate and the associated proteins construct the mitotic spindle before the initiation of mitosis. The process has been found to initiate with the coiling as well as thickening of chromosomes in prophase. The nucleolus has been found to include a spherical structure which finally reduces and vanishes. The formation of a fibre clump has been found to be in the form of spindle and the nuclear membrane dissolution associated with prophase ending signal.

The genetic information of most cells in the body is maintained, fixed, and handed on to daughter cells in a highly coordinated and regulated process. However, there are several instances during the cell cycle when the cycle or a regulatory mechanism makes a mistake, causing the cell to grow uncontrollably, eventually leading to cancer. Somatic cells are the most well-known cells in this cycle, which comprises two main phases: interphase and mitosis. Some subdivisions are necessary for cell division and the maintenance of genetic material during interphase. G1, S, and G2 are the three subdivisions (Maiato et al., 2015). When a cell is about to die, it might also enter a fourth phase known as G0.

The results demonstrate that the majority of the cells in the selected view are in the prophase stage. Only a few cells are in telophase, and even fewer are in anaphase or metaphase. As a result, it may be deduced that the selected view contained cells that had only recently began their cell cycle. By dividing the total number of cells present in each stage of mitosis by the total number of cells present in the view, the mitotic index was obtained (Schellhaus et al., 2016).

Prophase had the highest mitotic index, followed by telophase, anaphase, and metaphase. As a result, it was determined that the majority of the cell cells were in the early phases of cell division. A high mitotic index has been found to indicate that more cells are dividing. This is a significant factor for diagnosing almost all the cancer types. In other words, it can be said that the mitotic index is significant and it provides a measure of the ability of cells to divide and of the cell division rates (McIntosh, 2016).

The current experiment was only associated with observing the cell division process in a selected organism by using microscope. However, it can be stated that this technique can also be used in other disciplines of the medical field. The experimental findings have proved to be significant for the future experiments associated with mitosis. The importance of mitotic index in cancer has been stated in another research study also (Bakhoum et al., 2014). On the other hand, it has been observed that, mitotic index can also be used as an experimental process to study the cell division process in academics (Ohkura, 2015).

A heightened rate of mitotic index has been found to indicate that a greater number of cells are dividing at a unit time. In other words, it can be said that the mitotic index can be stated to be elevated when compared to the normal growth of tissues or the cellular repair at the injury sites.

A mitotic index has been found to indicate that the cell division rate increases along with the mitotic index and is also a sign to show whether the cells are at a cancerous stage or not. Thus, for future experiments, the use of mitotic index, will be beneficial for understanding whether a human host is at the danger of developing cancer or not.

References

Bakhoum, S. F., Kabeche, L., Murnane, J. P., Zaki, B. I., & Compton, D. A. (2014). DNA-damage response during mitosis induces whole-chromosome missegregation. Cancer discovery, 4(11), 1281-1289.

Dominguez-Brauer, C., Thu, K. L., Mason, J. M., Blaser, H., Bray, M. R., & Mak, T. W. (2015). Targeting mitosis in cancer: emerging strategies. Molecular cell, 60(4), 524-536.

Maiato, H., Gomes, A. M., Sousa, F., & Barisic, M. (2017). Mechanisms of chromosome congression during mitosis. Biology, 6(1), 13.

McIntosh, J. R. (2016). Mitosis. Cold Spring Harbor Perspectives in Biology, 8(9), a023218.

Minocherhomji, S., Ying, S., Bjerregaard, V. A., Bursomanno, S., Aleliunaite, A., Wu, W., ... & Hickson, I. D. (2015). Replication stress activates DNA repair synthesis in mitosis. Nature, 528(7581), 286-290.

Ohkura, H. (2015). Meiosis: an overview of key differences from mitosis. Cold Spring Harbor Perspectives in Biology, 7(5), a015859.

Schellhaus, A. K., De Magistris, P., & Antonin, W. (2016). Nuclear reformation at the end of mitosis. Journal of molecular biology, 428(10), 1962-1985.

Vicente, J. J., & Wordeman, L. (2015). Mitosis, microtubule dynamics and the evolution of kinesins. Experimental cell research, 334(1), 61.