Question

There are two major types of cell death, necrosis and apoptosis.

1. Compare and contrast the two major types of cell death, necrosis and apoptosis.

2. There are three main pathways of apoptotic cell death. Describe the pathways including induction, cells involved, main chemical mediators (pro-and antiapoptotic) and receptors and outcomes

Answer 1

Ans 1)

Necrosis:-

i) Necrosis is known to be a kind of cell death where the cell lies in an ultimate way due to some uncontrolled external factors.

ii) Necrosis is caused by factors external to the cell or tissue such as infections and toxins which result in untegulated digestion of cell components.

iii) Necrosis causes loss of membrane integrity and random degradation of DNA.

Apoptosis:-

i) Apoptosis is defined as a predifined suicide cell where the cell destroys itself maintaining a smooth functioning of the body.

ii) Apoptosis is a naturally occuring programmed and targetted cause of cellular death.

iii) Membrane blebbing occurs in apoptosis but integrity of the membrane is maintained and chromatin condensation as well as non random degradation of DNA.

Ans 2)

The three main pathways of apoptopic cell death are:- Intrinsic pathway, extrinsic pathway and perforin/granzyme pathway.

Intrinsic pathway:-

The stimuli that initiate the intrinsic pathway produce intracellular signals they may act in either a positive or negative fashion. Negative signals involve absence of certain growth factors and poaitive signals consits of cytochrome C.  It also includes Apoptosis inducing factor, inhibitots of apoptosis proteins and caspacase 3.

Extrinsic pathway:-

Extrinsic initiation pathway includes receptors of TNFR (Tumor Necrosis Factor Receptor). It includes flice like imhibitory protein, caspase 8 and cell death receptors - TNFR 1, CD95 and TRAILR 1 plus TRAILR 2.

Perforin Pathway:-

One of the main aspect of adaptivr immune system is recognizing and eliminating target cells through the induction of apoptosis involving CD8+ cytotoxic T lymphocytes and Natural Killer cells. It also includes killer cell immunoglobulin receptor and killer cell lectin like receptors.