Apoptosis And Necrosis Comparison Essay

Apoptosis vs Necrosis
(Similarities and Differences)

Apoptosis and Necrosis are two types of cell death occur in organisms. The cells undergo death when the cell death becomes necessary as a part of developmental process or they fail to adapt to injuries. Both these types of cell deaths differ in their initial cause and progression of the cell death pathway.

Apoptosis definition (programmed cell death): a physiological process by which unwanted or useless cells are eliminated during the development and other normal biological processes. Often found during tissue homeostasis, embryogenesis, immunological reactions and development of nervous systems. During apoptotic cell death, the cells undergo some characteristic events such as chromatin condensation, nuclear and cytoplasmic aggregation and partitions of cytoplasm and nucleus into membrane bound vesicles called apoptotic bodies containing ribosomes and mitochondria. Apoptotic bodies are recognized and phagocytized by either by macrophages or adjacent cells and thus no inflammatory response are elicited during apoptotic cell death.

Necrosis definition: (accidental cell death) a pathological process occurs when the cells are exposed to serious physical or chemical insults. Occur during pathological infections such as bacterial and fungal infections, hypothermia and hypoxia conditions. The cell and cellular organelles swell and ruptures to release the entire cell content including lysosomal enzymes into the extracellular fluid.  Due to this, necrotic cell deaths are always associated with severe inflammatory response in the surrounding tissues.

The current post describes the similarities and difference between apoptotic and necrotic cell death with a comparison table.

Similarities between Apoptosis and Necrosis

Ø  Both apoptosis and necrosis are cell death pathways in organisms

Ø  Both are characterized by profound membrane dysfunctions

Ø  Both are characterized by mitochondrial dysfunctions

Ø  In both apoptosis and necrosis, the DNA get fragmented

Ø  The remnants of both apoptotic and necrotic cell death are phagocytosed

Ø  Apoptosis and necrosis occurs both in plants and animals (mechanism varies)

Ø  Both apoptosis and necrosis are absent in prokaryotic cells

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Difference between Apoptosis and Necrosis

Sl. No.ApoptosisNecrosis
1Apoptosis is a ‘programmed’ cell deathNecrosis is a ‘premature’ cell death
2Apoptosis is a highly regulated timely eventNecrosis is an unregulated random event
3Genetically ControlledNot Genetically controlled
4Apoptosis is a pre-planned cell death pathwayNecrosis is not a pre-planned cell death pathway
5Apoptotic cell deaths are natural/normalNecrotic cell deaths are always pathological (not natural)
6Apoptotic cell death usually do not require any treatmentNecrotic cell death are not naturals and always require proper treatment
7Apoptotic cell deaths are usually beneficial to the organismsNecrotic cell deaths are always detrimental to the organisms
8Apoptotic cell death is initiated by self-generated signals from inside or outside the cellsNecrotic cell death always occurs after signals from external agents such as fungal or bacterial toxins
9Shrinkage of cells occurs during apoptosisSwelling of cells occurs during necrosis
10Membrane blebbing occurs during apoptotic cell deathNo membrane blebbing but the membrane get disrupted during necrotic cell death
11Chromatin condensation is a hallmark of apoptosisNo chromatin condensation occurs during necrosis
12Nucleus get fragmented Nucleus get disorganized
13Apoptotic bodies are formed during apoptotic cell deathNo such necrotic bodies are formed during necrosis
14Usually apoptotic cell death is devoid of any physical symptomsSevere inflammatory symptoms are evident in the neighboring cells after necrotic cell death
15No inflammation occurs in the surrounding tissuesCause severe inflammation in the surrounding tissues
16Cell undergoing apoptosis are actively take part in cell death pathway Cells undergoing necrosis do not take part in any events in the death pathway
17An active process hence require energy from ATP moleculesA passive process and do not require ATP
18Since it is an active process, apoptosis does not occur at 4oCSince it is a passive process, necrosis can also occur at 4oC
19Phagocytosis of the cell remnants are done by the adjacent cells or macrophagesPhagocytosis of the cell remnants are always done by the macrophages
20The integrity of lysosomes are preserved in apoptotic cell deathThe integrity of lysosomes are compromised during necrotic cell death, lysosome leakage occurs
21The integrity of mitochondria usually lost during the initial phases of apoptosisThe integrity of mitochondria usually maintained during the initial phases of necrotic cell death
22Apoptosis is a Caspase dependent cell death pathwayNecrosis is a Caspase independent cell death pathway
23Activation and participation of many Cascase enzymes are involved in apoptosisNo Caspase enzymes are involved in necrosis
24Externalization of phosphatidyl serine from inner to the outer leaflet of plasma membrane occursNo such flipping of plasma membrane occurs during necrotic cell death
25DNA fragmentation is pre-lytic (before cell lysis) in apoptosisDNA fragmentation is post lytic (after cell lysis) in necrosis
26DNA is fragmented between nucleosomes and hence a ladder like pattern is formed after the agarose gel electrophoresis of total DNA extractDNA fragmentation is random and hence not ladder but a smear like pattern is formed after agarose gel electrophoresis of total DNA extract
27Release of cytochrome C and AIF from the mitochondria to the cytoplasm of cells occursNo such events are reported in necrosis
28pH of the cells changes to acidic during apoptosisThere is no change in the pH of the cells during necrosis
29Apoptosis ends in fragmentation of cells into smaller bodies (apoptotic bodies)Necrosis ends in total lysis of the cells
30Usually apoptotic cell death occurs in individual cellsUsually a group of cells undergo necrotic cell death

(image source cc Wikipedia)

Posted in Cell and Molecular Biology, Cell Biology, Difference Between..., Molecular Biology and tagged Apoptosis, Cell Cycle Checkpoints, Cytology, Life Science NET Study Materials, Molecular Biology, Necrosis.

3 Pathological processes - cell death

3.1 Apoptosis and necrosis

When cells die, they do so in two main ways: by apoptosis or necrosis (Figure 10). Apoptosis is programmed cell death; the cell dies as part of its normal programme of development, or it may be lacking in growth factors, or it may be instructed to die by cells of the immune system, because it has become infected. Even pre-cancerous cells may be propelled into apoptosis, by the normal cellular controls that check the development of tumours. In all cases, apoptosis is a highly ordered process. If it occurs as part of a developmental process, it does not induce inflammation - the dead cells are quietly removed by phagocytes within the tissue. Hence, it is often very difficult to identify apoptotic cells within tissues, since they are usually individual cells, with small condensed nuclei and little cytoplasm. Cell death in degenerative conditions (e.g. Alzheimer's disease) appears to occur by apoptosis. Although the loss of individual cells is histologically undramatic, the cumulative loss of cells in such degenerative conditions can cause major loss of function in the affected tissue. Moreover, cell loss may be accompanied by the accumulation of products of tissue breakdown, which are histologically evident.

Figure 10 Schematic diagram comparing the events that occur in cells undergoing death by necrosis (left) or apoptosis (right). The first events in necrosis are irregular condensation of chromatin, swelling of the mitochondria and breakdown of membranes and ribosomes. The cell is eventually disrupted, releasing its contents and inducing an inflammatory reaction. In contrast, a cell undergoing apoptosis shows condensation of the nucleus into fragments and shrinkage of the cell. The nucleus and cytoplasm break up into fragments called apoptotic bodies, which are phagocytosed by mononuclear phagocytes.

In contrast necrosis is wholesale unregulated cell death caused by lack of nutrients or infection. For example the failure of the blood supply to an organ due to thrombosis (see below) will cause massive cell death due to lack of oxygen (ischaemia). A large area of cell death caused by ischaemia is called an infarction. Another example of cell necrosis is seen in severe viral infections with cytopathic viruses (e.g. polio). Necrosis is an uncontrolled process and the dying cells release their contents. Areas of necrosis are characterised by infiltration with inflammatory cells; macrophages and neutrophils enter the area over a number of days and weeks in order to clear the dead cells and associated cellular debris. Such large areas of cell loss and inflammation are frequently easily seen in pathological specimens, even without microscopic examination (Figure 11).

Figure 11 An area of necrosis in the lung caused by a thromboembolism is visible on the left of this section. The area on the right includes surviving lung tissue, which is thickened and has areas of fibrosis. Scale bar = 2mm.

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