Abstract
The overviews task of cell division is constant with all living things especially true when it comes to biology in particular cell-division cycle. Organisms are constantly dividing and growing throughout their lifetime. The cell-division cycle in eukaryotes is a complex process that involved cyclins and multiple point that actually leads to cell division. In biology, there are two different types of cell division, which are Meiosis and Mitosis. Meiosis is the type of cell, which involved sex cells in a sexual reproduction.
Cell Division
The process of cell division plays a key roles in everyday life of human beings and as well as living organisms. Due to Rudolf Virchow (1855), a German physician said that “Where a cell exists, there must have been a pre-existing cell, just as the animal arises only from an animal and the plant only from a plant” If cell division were not active in life, all living organisms would cease to reproduce and eventually perish because of it. Within cell division, there are key roles knows as nuclear division and cytokinesis. There are two types of cell within nuclear division, which are Mitosis and Meiosis.
Mitosis and Meiosis play an effective role in everyday life; Meiosis is a sex cell, which involved in a sexual reproduction. This type cell division produce four different cell from haploid cell from original diploid cell due to the crossing over of chromosomes during cell division. In a way, the cell-division cycle is also involved in sexual reproduction when two gametes are fuses together in order in other to create a living organism that is made of complex cells and organs.
Mitosis is the type of cell division, which involved regular cells in the body. This cell division is a normal haploid cell, which is replicated and divided into two identical cells. The resulting cells are identical because there are no sex involved crossing over chromosomes does not take place. Mitosis defined to as binary fission in prokaryotes where one cell is divided into two identical cell types. When a cell first enters cell- division cycle, it needs to take in certain necessary nutrients, which it acquires during interphase. This phase prepares the cell for more cell division in the future. (Alberts, et al., 2010).
Stages of the Cell Cycle
The cell cycle has two major phase called interphase and the mitotic phase. During this phase, the cell grows and DNA id replicated, while mitotic phase, the replicated DNA and cytoplasmic contents are separated and the cell divides. The mitotic phase (also known as M phase) is a multistep process during which the duplicated chromosomes are aligned, separated, and move into two new, identical daughter cells. During mitotic phase, nuclear division, karyokinesis will occur. There are 4 stages in Mitosis namely Prophase, Metaphase, Anaphase and Telophase.
There are three stages of interphase called G1, S, and G2.
‘G1’ Phase: Cell doubles its organelles and Cell grows in size
‘S’ Phase: DNA replication and each Chromosome forms 2 identical Sister chromatids.
DNA is in very long threads. DNA associated with histone proteins which is called ‘chromatin’. Chromatin breaks in to small bits and condenses (coils) to form ‘chromosomes’. (Each species has certain number of chromosomes – Humans 46, Corn 20 & Goldfish 94. Each chromosome duplicate and produce 2 sister chromatids and they are attached together by centromere while ‘G2’ Phase: Cell grows in size and prepares for mitosis.
Mitosis in Animal Cells: Prophase Sister chromatids are clearly visible, Nucleolus disappears, Nuclear envelope disintegrates and Centriole will produce spindle fibers. (Microtubules grow out from each centrosome with their ends growing toward the center of the cell (metaphase plate). These clusters of microtubules are called spindle fibers).
Mitosis in Animal Cells: Metaphase
Centromere of each chromosome develops two kinetochores,
(specialized protein complex), they physically hook /help to attach sister chromatids with spindle fiber. Chromosomes, (made up of sister chromatids), are pulled by spindle fibers and forced to align across equatorial plane /central region /metaphase plate of cell.
Mitosis in Animal Cells: Anaphase
- Due to the contraction of the spindle fiber, centromere breaks in the middle, separating the two sister chromatids apart.
- Sister chromatids are pulled to opposite poles by the spindle fiber. Each sister chromatid is now called daughter chromosomes.
Mitosis in Animal Cells: Telophase
Spindle fiber will disappear. Centromere will disappear. Two clusters of chromosomes are resulted at each pole. Around each cluster, nuclear envelopes form. Nucleolus reappears. Chromosomes uncoil and become chromatin again. Resulting in two daughter nuclei inside a parent cell.
Cytokinesis: Animal Cells
Mitotic phase, will be followed by cytokinesis, the division of cytoplasm will occur resulting in the physical separation of the cytoplasmic components into the two daughter cells. Division of cytoplasm into two, often begins in anaphase.
Animal cytokinesis: A cleavage furrow appears between 2 daughter nuclei. (Formed by a contractile ring of actin filaments). Eventually pinches parent cell in two.
Meiosis brings about genetic variation in two ways: one is crossing over and independent assortment. Crossing over exchange of genetic material between non-sister chromatids of homologous chromosomes during meiosis I. While Independent assortment Then homologues chromosomes separate and are distributed to different daughter cells.
Changes in Chromosome Structure
- Deletions: One or both ends of a chromosome breaks off leading to loss of an internal segment
- Duplications: Presence of a chromosomal segment more than once in the same chromosome
- Inversions: Occurs as a result of two breaks in a chromosome. The internal segment is reversed before re-insertion and genes occur in reverse order
- Reciprocal Translocations: Exchange of segments between non-homologous chromosome.
References
- “Cell Division | Biology | Science.” Khan Academy, Khan Academy, www.khanacademy.org/science/biology/cellular-molecular-biology.
- “Cell Division.” Cell Division – an Overview | ScienceDirect Topics, www.sciencedirect.com/topics/neuroscience/cell-division.
- Kazilek. “Cell Division.” Kazilek, 3 Feb. 2014, askabiologist.asu.edu/cell-division.
- Nature News, Nature Publishing Group, www.nature.com/scitable/topicpage/mitosis-and-cell-division-205/.
- “What Is Meiosis?” Facts, The Public Engagement Team at the Wellcome Genome Campus, 6 May 2016, www.yourgenome.org/facts/what-is-meiosis.
