Apoptosis or Cell Death

Introduction

The term apoptosis is of Greek origin meaning dropping or falling off. It was first introduced by Kerr, Wyllie, and Currie. Tissues and cells undergo a periodic ware and tare. In the midst of such a process, if there is abnormal cell damage and death, then the survival of organisms is at stake. In order to continue the life and generations of life of a multicellular organism, the organism depends on the ability to either regulate the turnover of cells or limit the injury that they witness.  "Apoptosis is used for a natural biological process of programmed cell death in which the cells destroy themselves for maintaining the smooth functioning of the body.”

 

Contents

1. Introduction

2. Characteristics of apoptosis

3. Difference between cell necrosis and apoptosis

4. Need for apoptosis 

5. Process of apoptosis

 

Characteristics of apoptosis

The process of apoptosis is an energy-dependent, tightly regulated physiologic process. Cells undergoing apoptosis exhibit membrane blebbing, nuclear condensation, and degradation of DNA into large fragments of uniform length. 

Difference between cell necrosis and apoptosis

A sequential wave of programmed cell death is necessary for normal development during embryogenesis, or during any cell injury, infections throughout life. Cell necrosis or death of tissues is a passive form of cell death that is induced by non-physiologic agents (not from within). For example, diabetic foot, cancer of certain types. Necrosis in simple terms is irreversible and abnormal because this is what the body doesn’t want whereas apoptosis is a necessity.

Need for apoptosis 

Cells need a periodic cleaning where the set of old and redundant groups must be removed, in addition, tissues must be resolved by removing the cells with dysfunctional DNA and chromosomes. On a daily basis, 50 – 80 billion cells die in a normal adult due to apoptosis. Apoptosis makes the body refreshed by removing the infected cells, aged cells, pre-cancerous cells, and other redundant masses. Hence, apoptosis is a normal requirement and essential for bringing in the balance within a system. Apoptosis can also occur in different forms if you take an example of a cobra, it sheds it`s outer layer 4-6 times in a year, it is indeed a normal process. Another classical example of apoptosis is the loss of the tail of a tadpole when it turned into a mature frog.

Process of apoptosis

There are 2 independent pathways to initiate the process, namely the intrinsic and extrinsic pathways. Explanation for the 2 pathways is as under. Intrinsic Pathway, as the name suggests, is a response to internal stimuli or triggers like biochemical stress, damage, infections, trigger for cancerous cells, etc. Extrinsic Pathway triggers apoptosis in response to some external stimuli like an injury. This can be in response to ligand binding at death receptors on the cell surface.  One of the classical examples is DNA damage ( genetic errors as shown in the image) which can activate the p-53 gene that halts the cell cycle. In the next phase, there is an initiation of DNA repair. If the DNA repair fails the ultimate result could be induced apoptosis. In addition to cell injury, apoptosis may also result from a lack of growth in a normal cell (redundancy). 





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