“The term apoptosis can be defined as a natural biological process of programmed cell death in which the cells destroy themselves for maintaining the smooth functioning of the body.”
What is Apoptosis?
There are two forms of cell death
- Programmed death of cells called Apoptosis.
- An uncontrolled death of cells called Necrosis.
Both apoptosis and necrosis occur under different circumstances and involve different steps.
The term apoptosis is derived from the Greek word meaning dropping or falling off. It was first introduced by Kerr, Wyllie, and Currie.
Apoptosis is a biological process which occurs in all multicellular organisms including plants and animals. It removes the cells from the organisms that should no longer be a part of the organism. This process plays a major role in the development of humans and in developing and maintaining a healthy immune system.
On an average, 50 – 80 billion cells die every day in a human adult due to apoptosis. During this biological process, infected cells, pre-cancerous cells and other cancer cells are eliminated successfully and maintain the balance of cells in the human body. Therefore, it is an essential process that is responsible for the normal development of cells, cell cycle maturation and maintaining the regular functions and activities of cells.
Apoptosis occurs in all the vertebrates that have fingers and toes like digits. A slight mistake during apoptosis results in fused toes or fingers. The loss of the tail of a tadpole when it develops into a frog is yet another example of apoptosis.
Also Read: Difference between apoptosis and necrosis
The process of apoptosis undergoes two pathways:
- Extrinsic Pathway
- Intrinsic Pathway
This pathway triggers apoptosis in response to external stimuli, like, ligand binding at death receptors on the cell surface. These receptors are members of the Tumor Necrosis Factor gene family. The receptor binding initiates caspase activation.
This pathway triggers apoptosis in response to internal stimuli such as biochemical stress, DNA damage and lack of growth factors. This pathway is modulated by two groups of molecules- Bax, and Bcl-2. These groups of molecules determine whether a cell will survive or undergo apoptosis in response to the stimuli.
Significance of Apoptosis
Apoptosis is significant for the following reasons:
- It helps to maintain homeostasis in the multicellular organisms.
- Proper size of the body is maintained by apoptosis.
- Apoptosis maintains the constancy of cell number in an organism.
- The unwanted cells are eliminated from the body by apoptosis.
- The dangerous T-lymphocytes are eliminated by apoptosis.
- Programmed cell death is crucial for cell development.
Role Of Apoptosis
Apoptosis plays an important role in the body of an organism. Following are a few such roles performed by the process:
- The separation of the fingers during the development of the foetus is due to apoptosis.
- It results in the closure of the neural tube in the dorsal part.
- Programmed cell death results in the removal of vestigial remnants such as pronephros.
- During the determination of sex of the foetus, the Wolffian ducts are removed by cell death.
- In the urachus, apoptosis allows the removal of redundant tissues between the bladder and umbilicus.
Relationship Between Apoptosis and Cancer
Cancer is the uncontrolled division of cells that leads to the development of tumour. If the apoptotic signalling works properly, these unwanted cells can be removed from the body. The main reason for cancer is that they have the ability to prevent apoptosis and therefore multiply uncontrollably.
Also Read: Senescence
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Frequently Asked Questions
How is apoptosis important?
Apoptosis eliminates the pre-cancerous and virus-infected cells. It thus maintains a balance of cells in the human body and enhances the immune system.
Give an example of apoptosis.
As the tadpole transform into a frog, it destroys and reabsorbs its entire structures. As the tadpole matures, the cells from its gills, fins, and tail die by apoptosis signals.