Course material

1. Answers: Introduction Background Cell cycle is the process in which
Answers:
Introduction
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 (6th 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).

2. 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.
Aim And Objectives
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 –
To analyse the mitotic stages in mitosis.
To differentiate the mitosis stages by a light microscope.
To count the number of cells in each mitosis stages in the view of light microscope.
To calculate the mitotic index of each stage of mitosis, observed in a light microscope.
Results
Fig 2: Mitotic cells observed through light microscope
Source: Laboratory
Total number of cells = 186
Total number of cells in prophase – 162

3. 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.
Discussion
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

4. 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.

5. 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.