Introduction:
- Cell division is the process by which cells divide and replicate their DNA in order to produce new cells. There are two main types of cell division: mitosis and meiosis.
- Mitosis is the process by which cells divide to produce two daughter cells that are genetically identical to the parent cell. It occurs in eukaryotic cells, which are cells that have a true nucleus and membrane-bound organelles.
- During mitosis, the chromosomes in the nucleus of the parent cell are replicated, and the two copies of each chromosome are separated and moved to opposite poles of the cell. The cell then divides into two daughter cells, each of which receives one copy of each chromosome. This process ensures that the genetic information is accurately transmitted to the daughter cells.
- Mitosis plays a vital role in the growth and repair of multicellular organisms, as it allows cells to divide and produce new cells when needed. It also plays a role in the development of embryos and the maintenance of tissue homeostasis.
- Meiosis, on the other hand, is a type of cell division that produces four genetically diverse daughter cells from a single parent cell. It occurs in the production of gametes, such as sperm and eggs, and is essential for sexual reproduction. During meiosis, the DNA of the parent cell is replicated and the chromosomes are separated into four daughter cells, each of which receives a unique combination of chromosomes. This process generates genetic diversity, which is important for the survival and evolution of species.
Phases:
Mitosis is a type of cell division that occurs during the cell cycle, which is the series of events that take place in a cell leading up to and following cell division. The cell cycle consists of two main phases: interphase and the mitotic phase.
Fig: Cell cycle
Interphase
Interphase is the period between cell divisions and is divided into three subphases:
G1 phase: During the G1 phase, the cell grows and performs its normal functions.
S phase: During the S phase, the DNA of the cell is replicated.
G2 phase: During the G2 phase, the cell prepares for mitosis by synthesizing proteins and organelles that will be needed during cell division.
Mitotic phase
The mitotic phase is the phase of the cell cycle in which cell division occurs. It is divided into several subphases:
Prophase: During prophase, the replicated chromosomes become visible and the nuclear envelope begins to break down. The mitotic spindle also begins to form.
Metaphase: During metaphase, the replicated chromosomes line up at the equator of the cell, with one copy at each pole. The mitotic spindle becomes fully formed.
Fig: Stages of Mitosis
Anaphase: During anaphase, the replicated chromosomes are separated and move to opposite poles of the cell, carried by the mitotic spindle.
Telophase: During telophase, two new nuclei form at opposite poles of the cell, and a new cell wall begins to form between the two daughter cells.
Fig: Stages of Mitosis
Cytokinesis: Cytokinesis is the process by which the cytoplasm of the parent cell is divided into two daughter cells. In animals, this process involves the formation of a cleavage furrow in the cell membrane, while in plants it involves the formation of a cell plate.
Fig: Stages of Mitosis
Function:
Mitosis plays several important roles in the growth and development of multicellular organisms. Some of the key functions of mitosis include:
Growth: Mitosis allows cells to divide and produce new cells, which is essential for the growth and development of multicellular organisms.
Repair: Mitosis allows cells to replace damaged or dead cells, helping to maintain the health and function of tissues and organs.
Development: Mitosis plays a crucial role in the development of embryos, allowing cells to divide and differentiate into the various cell types and tissues needed to form a functional organism.
Homeostasis: Mitosis helps to maintain tissue homeostasis by allowing cells to divide and replace old or damaged cells. This helps to maintain the proper function of tissues and organs.
Asexual reproduction: Some organisms, such as bacteria and fungi, reproduce asexually through the process of mitosis. This allows them to rapidly produce offspring and colonize new environments.
Mitosis as a Diagnostic Marker:
- Mitosis is a process that occurs in all actively dividing cells, and it can be used as a diagnostic marker in certain situations. For example, the presence of abnormal mitosis in cells can be an indication of cancer or other diseases. The examination of mitosis can be an important tool in the diagnosis and treatment of various medical conditions.
- In cancer, the normal process of cell division becomes disrupted, and cells may divide in an uncontrolled or abnormal way. One way that cancer cells can be distinguished from normal cells is by examining the way that they divide during mitosis. Cancer cells may exhibit abnormal mitosis, such as chromosomal abnormalities or misaligned chromosomes, which can be detected under a microscope.
- Additionally, the rate of mitosis in a tissue can be used as a diagnostic marker for certain conditions. For example, a high mitotic index (the number of cells undergoing mitosis in a given tissue) can be an indication of cancer or other abnormal cell growth. Conversely, a low mitotic index can be an indication of tissue damage or degeneration.
Difference between mitosis and meiosis:
Mitosis and meiosis are two types of cell division that have different functions and outcomes.
- Mitosis is the process by which a single cell divides into two identical daughter cells. It is a type of asexual reproduction that occurs in somatic cells, which are cells that make up the body of an organism. During mitosis, the cell’s nucleus divides into two identical copies, and the cytoplasm is divided equally between the two daughter cells. This ensures that each daughter cell receives a complete set of genetic material and is able to function normally.
- Meiosis, on the other hand, is the process by which a single cell divides into four non-identical daughter cells. It is a type of sexual reproduction that occurs in the cells that produce gametes, such as eggs and sperm. During meiosis, the cell’s nucleus divides into four daughter cells, each of which receives a unique combination of genetic material from the parent cell. This results in genetic diversity among the daughter cells, which is important for the survival of a species.
Here are some key differences between mitosis and meiosis:
Purpose: Mitosis is used for growth, repair, and maintenance in an organism, while meiosis is used to produce gametes for sexual reproduction.
Number of daughter cells: Mitosis produces two daughter cells, while meiosis produces four daughter cells.
Genetic material: Mitosis produces daughter cells that are genetically identical to the parent cell, while meiosis produces daughter cells with a unique combination of genetic material.
Chromosome number: During mitosis, the number of chromosomes in the daughter cells is the same as the number in the parent cell. During meiosis, the daughter cells have half the number of chromosomes as the parent cell.
Genetic variation: Mitosis does not produce any genetic variation, while meiosis produces a large amount of genetic variation through the process of crossing over and independent assortment.
Difference between animal and plant cell mitosis:
In total, while there are some differences between animal and plant cell mitosis, the basic process of cell division is similar in both types of cells. Here is a summary of the main differences between animal and plant cell mitosis:
Cell wall: Plant cells have a cell wall that surrounds their cell membrane, while animal cells do not. This means that during cell division, plant cells must produce a cell plate that will eventually develop into the cell wall of the daughter cells.
Mitotic spindle formation: In animal cells, the mitotic spindle is formed by microtubules that grow out from the centrosomes, which are located at opposite ends of the cell. In plant cells, the mitotic spindle is formed by microtubules that grow out from the centrosomes as well as from the cell cortex, which is the layer of cytoplasm just beneath the cell membrane.
Cytokinesis: During cytokinesis, the cytoplasm of the cell is divided into two daughter cells. In animal cells, cytokinesis occurs by the formation of a cleavage furrow, which is a shallow indentation in the cell membrane that eventually deepens and divides the cell into two daughter cells. In plant cells, cytokinesis occurs by the formation of a cell plate, which eventually develops into the cell wall of the daughter cells.
Chromosome movement: During mitosis, the chromosomes are moved to opposite poles of the cell. In animal cells, the chromosomes move along microtubules that extend from the centrosomes to the poles of the cell. In plant cells, the chromosomes move along microtubules that extend from the centrosomes and the cell cortex to the poles of the cell.
Importance of mitosis in cell division:
- Growth and development
- Tissue repair and regeneration
- Asexual reproduction
- Development of multicellular organisms
- Continuity of life
Mitosis and cancer:
Cancer is defined by uncontrolled cell division, hence mitosis and cancer are mutually dependent. Cancer cells frequently have abnormalities in genes that control the cell cycle, altering the usual regulation systems that ensure orderly cell division. These mutations can cause problems with the mitotic machinery, resulting in incorrect chromosomal segregation, genomic instability, and the accumulation of genetic mistakes. Furthermore, cancer cells proliferate more because mitotic processes are dysregulated. In addition, cancer cells’ ability to metastasis is dependent on their ability to undergo unusual mitosis, which allows invasion of surrounding tissues and distribution to distant places. Understanding the relationship between mitosis and cancer is critical for developing targeted therapeutics aimed at disrupting abnormal cell division and slowing cancer growth.
References:
- Pollard, T.D., Earnshaw, W.C., Lippincott-Schwartz, J. and Johnson, G., 2016. Cell biology E-book. Elsevier Health Sciences.
- Johnson, M., 2002. Introductory biology online. Journal of College Science Teaching, 31(5), p.312.
- Rastogi, S.C., 2006. Cell and molecular biology. New Age International.