Biological complexity: programmed cell death (Introduction)

by David Turell , Thursday, February 16, 2023, 21:13 (435 days ago) @ David Turell

Several kinds:

https://www.the-scientist.com/sponsored-article/programmed-cell-death-mechanisms-for-ce...

"Over the years, researchers have described many forms of PCD. This summary provides a brief overview of three types—apoptosis, pyroptosis, and necroptosis–and their importance in health and disease.

"In general, PCD can be either lytic or non-lytic. During lytic cell death, the contents of a dying cell are released into the surrounding space as the cell’s membrane becomes damaged. In contrast, non-lytic cell death secludes the cellular remains in multiple apoptotic bodies before they are discarded.

"Apoptosis is a form of non-lytic PCD that involves condensation of the nucleus and cytoplasm, chromosomal cleavage, and plasma membrane blebbing.

***

"Intrinsic apoptosis occurs when a cell is damaged on the inside or is facing a stressful internal condition, such as DNA damage or nutrient deprivation. These conditions cause the mitochondrial outer membrane to permeabilize and release cytochrome C.1 Cytochrome C helps apoptotic protease-activating factor 1 (APAF-1) proteins assemble into a larger unit in the cytoplasm. APAF-1 is key during apoptosis because it contains a caspase recruitment domain (CARD), which activates protease enzymes called caspases that cleave proteins.

"Unlike intrinsic apoptosis, extrinsic apoptosis is triggered by a signal outside of the cell and requires membrane-spanning proteins called death receptors. The external signal, or death ligand, can come from another cell or environmental response. Activation of death receptors by death ligands such as Fas, tumor necrosis factor (TNF), or TNF-related apoptosis-inducing ligand (TRAIL), recruits two proteins to form a death-inducing signaling complex (DISC), which activates a different set of caspases from intrinsic apoptosis.

*** several rare mechanisms skipped for brevity

"Autophagy is often used by cells as a survival mechanism to protect itself from nutrient deprivation, oxidative stress, endoplasmic reticulum stress, etc.11 Here, the cytoplasm is sequestered and packaged for degradation by the lysosome, rather than being release into the extracellular space. In many cases, the material that is degraded by the lysosome can be recycled and used again as starting materials, such as amino acids for protein synthesis or carbohydrates for energy production."

Comment: obviously cells constantly develop damage or garbage. The body is in constant cleanup mode. These different mechanisms are highly complex and must have been present as cells appeared. That puts it in the realm of irradicably complex requiring design.