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Mitosis

Introduction refers to the duplication of the parent cell into two identicaldaughter cells. The DNA of the parent cell duplicates and theresulting daughter cells have the same genetics as the original cell. occurs in all eukaryotic cells (cells that have a nucleus).Each resulting daughter cell has an equal number of chromosomes withthe parent cell. The whole process of mitosis consists of six phases,namely: Interphase, prophase, prometaphase, anaphase and telophase. is a significant process in the life of different organisms.Growth and development of new membranes, fibres and tissues oforganisms occurs through mitosis. Single celled organisms such as anamoeba reproduce asexually through mitosis. Replacement of worn outcells by new identical cells take place through mitosis. In the samemanner, red blood cells are worn out easily and new red blood cellsform through mitosis (Goldberg 21).

Phasesof mitosis

Interphase Technicallyspeaking, interphase is not a stage of mitosis, but rather a restingstage before joining prophase. In this phase, the cell undergoes itsnormal process of growth while accumulating energy and nucleic acid.The cell prepares itself for another process of mitosis that startsin the phase of prophase. Cells are able to grow because they produceproteins and other cytoplasmic organelles. Chromosomes duplicateduring this phase as the cell prepare to join mitosis. At the time ofleaving the phase, the cell has enlarged, chromosomes have replicatedand centrioles (organizational sites for microtubules) replicate too.At this phase, the chromosomes may not be visible but a dark spotreferred to as nucleolus may be visible (Cregan 9).

Prophase Thenucleus of a cell contains substances known as chromatids, but theyare not visible during interphase. During this phase, the chromatidscondense and begin to form chromosomes that can be seen using a lightmicroscope. The visible chromosomes consist of two sister chromatidsthat are joined together by a protein known as the centromere.Nucleolus that is initially visible during interphase disappears. Apair of centrioles found close to the nucleolus start moving toopposite ends of the cell in this stage. Spindle fibre networks formduring this phase and they push the microtubules to the opposite sideof the cell.

Figure1: A cell during prophase

Source:Cregan and Elizabeth

Prometaphase Inthis phase, the process varies depending on the category of animals.In most multicellular organisms such as animals, the nuclear membranesurrounding the nucleus disappears and microtubules invade thenucleus through open mitosis. However, in some organisms such asfungi, the microtubules penetrate the nucleus through the intactmembrane and this is known as closed mitosis. During this phase, acomplex protein structure known as kinetochore is formed at thecentromere. Kinetochores are two and each of them attach itself to achromatid. Microtubules that have already developed attach themselvesto each kinetochore and this forces the chromosomes to start moving.The combination of kinetochore and microtubules produces sufficientenergy to separate the chromosomes’ two chromatids (Cregan 13).

Figure2: A cell during prometaphase

Metaphase Thecentre of a nucleus is referred to as the metaphase plate.Chromosomes align themselves at this metaphase plate and this isbrought about by several factors. First, it is during this stage thatthe spindle fibres attach themselves to the kinetochore. Chromosomesare pulled towards the ends of the cell by centrosomes through theirattached centromeres. The alignment of the chromosome towards thecentre of the nucleus is thought to be caused by the two opposingforces of the kinetochores. All chromosomes have to be aligned toavoid joining the next phase (anaphase) prematurely. The organizationof the chromosome along the equator is useful in ensuring that in thenext phase when chromosomes separate, each nucleus of the new cellsreceive a pair of the chromosome.

Figure3: A cell during metaphase

Anaphase Theseparation of chromosomes occurs in this phase. Half of thechromosomes are pulled on one pole of the spindle fibres while theother half move to the opposite pole. Spindle fibres shorten duringthis phase as the energy to sustain them is exhausted (Sircar 44).The contracting spindle fibres pull the sister chromatids apart andthus each chromatid move to the opposite end. The elongation offpolar microtubules forces the centrosomes and chromosomes to whichthey are attached to drift towards opposite sides of the cell. Thecentromeres are thought to move to different sides due to thebreakdown of microtubules. At the end of anaphase, all kinetochoremicrotubules degrade. The process enters its final phases known astelophase.

Figure4: A cell during anaphase

Telophase Thisphase signals the end of cell division. New membrane forms andencloses each daughter cell. Each chromatid has now reached theopposite pole of the cell. The increase in size of polar microtubuleselongates the cell even more. Nucleolus that disappeared duringprophase reappears during this stage. The chromosomes, now surroundedby new nuclei condense back to chromatids. Spindle fibres dissolveduring this phase. In short, this stage is the reverse of whathappened in prophase and prometaphase. ends at this phase,but cell division may not be complete. Cell partitioning may alsobegin at this phase (Rieder 8).Figure 5: A cell duringtelophase

Cytokinesis Thisis a separate process from mitosis that helps complete cell division.There is a notion that the cytokinesis is a part of telophase but inreality it is a different process that starts at the same time withtelophase.The process of cytokinesis differs between plants andanimals. In animals, there is a protein called actin at the centre ofthe cell that contracts and thus separate the cell into two similardaughter cells. The creation of two separate diploid cells from oneparent cell marks the end of cell division in animals. In plants,however, the plant cell has a rigid wall that requires a cell plateto be synthesized between the two daughter cells. At the end of thecytokinesis process, both mitosis and cell division are complete.

Conclusion is an important process that involves splitting of a mother cell intotwo similar daughter cells. As a process, mitosis has several phases,which are aligned to ensure complete duplication. Each phase hasunique roles that are not present in other phases and thus the phasesmay be said to be interdependent. Although some organisms such asprokaryotes duplicate through binary fission, most organisms usemitosis for cell division and these underlines the significance ofmitosis. Unicellular organisms such as an amoeba reproduce throughmitosis, growth and development of tissues, fibre and membranes areenabled by mitosis. Worn out cells such as skin cells are replacedthrough mitosis. Some organisms such as starfish regenerate bodyparts through mitosis. After every four months, red blood cells arereplaced through mitosis because of their short life span.

Works Cited

Cregan, Elizabeth. All about mitosis and meiosis. HuntingtonBeach, CA: Teacher Created Materials, 2008. Print.

Goldberg, Deborah. AP biology 2008. Hauppauge, N.Y: Barron`sEducational Series, 2007. Print.

Rieder, Conly L. and meiosis. San Diego: AcademicPress, 2009. Print.

Sircar, Sabyasachi. Principles of Medical Physiology.Stuttgart: Thieme, 2008. Print.