Back to David's theory of evolution: planned death (Evolution)

by David Turell @, Thursday, July 16, 2020, 22:08 (468 days ago) @ David Turell

Much of cell death is planned:

"Cells only have the physical disposal to contend with, so in the following discussion, one must not draw comparisons too tightly between human death and cell death.

"To a cell, dying really is a part of life. In fact, billions of cells die in the process of embryonic development, as our organs, fingers, and tissues are sculpted. That’s a wonderful thing. Nevertheless, tissues face real challenges in all stages of cell death, from deciding what cells need to bow out, to disposing of the “corpses” afterward. The cellular morgue is exquisitely designed for the challenge.


"While living, the cell keeps its lysosomes and proteasomes (molecular machines that recycle substrates) busy dismantling spent proteins and sending the components to recycling centers. Eventually, the whole cell’s work is done, or worse, has become infected and needs to commit hara-kiri. There’s an app for that. Apoptosis, programmed cell death, is a suite of tools and operations. Cells contain self-destruction kits, like spies with poison pills for use if captured. The poison pills consist primarily of the caspase family of proteins. Numbered caspase-1 through -14, these enzymes cut through (“cleave”) molecules like buzz saws.


"Processing of the apoptotic cell by the actions of activated caspases and their substrates, encapsulation of the cell into apoptotic bodies, and its subsequent disposal and recycling by surrounding phagocytic cells prevent the release of proinflammatory cellular contents and inflammation.


"Numerous actors come onto the stage when the apoptosis signal is triggered. In a sequence of steps, caspase-3 activates two other enzymes that create “find-me” signals that are sent out to attract wandering macrophages.


"In addition to the “find-me” signal, cells can post “eat-me” and “don’t-eat-me” tags on their outer membranes. Because don’t-eat-me tags take priority, these act as Boolean logic gates. The eat-me signal only activates the macrophage if the don’t-eat-me tag has been removed. Consequently, part of apoptosis includes removing the don’t-eat-me tags. This ensures that macrophages do not destroy healthy cells.


"Now that the phagocyte has found the cell to eat, how does it engulf the dying cell?

"Efferocytosis is a tightly regulated process involving the coordinated engulfment of dead and dying cells, maturation of the phagosome and then breakdown of phagolysosomal contents. Each stage is governed by molecular mechanisms that allow rapid breakdown of the engulfed cell and recovery of the engulfing phagocyte.


"A dizzying paragraph in the paper describes some 30 tools that create the “phagosome” (eating-body) that surrounds the dying cell or pathogen to engulf it safely without harming the phagocyte. The phagosome then delivers the contents to the recycling machines.

"Following recognition and entrapment of the dying cell, the phagosome and the cell corpse are destined for a well-orchestrated destructive end. The phagosome fuses with lysosomes, which contain a large variety of proteases, nucleases and lipases that digest the phagosome cargo...The phagosome containing the cell corpse is targeted to lysosomes through a multistep maturation process, which begins immediately following the formation of the phagosome on dynamin-dependent membrane scission and is marked by multiple biochemical changes at the phagosomal membrane….


"Once the phagosome has fused with lysosomes and its cargo has been degraded, a resolution phase restores homeostasis within the phagocyte, allowing further phagocytosis. Since dying cells are not the only phagocytic cargo, the outcome of phagocytosis can vary dependent on what cargo is internalized. In the context of efferocytosis, some of the components of the cell corpse can be recaptured and recycled for use by the phagocytic cell following lysosomal degradation. Sugars, amino acids, lipids and nucleotides are recycled to replenish cellular stores and can potentially be used as building blocks and an energy source by the phagocytic cell.


"The authors describe some of the terrible things that happen when components fail. Among them are autoimmune diseases, necrosis (accumulation of dead cells), neurodegenerative diseases like Alzheimer’s or Parkinson’s disease, multiple sclerosis, blindness, inflammation, atherosclerosis, liver disease, diabetes, impaired wound healing, rheumatoid arthritis, infertility, and cancer. (my bold)

"Efferocytosis is governed by a plethora of factors, including unique membrane lipids and multiple effector proteins, which mediate functions such as dead cell recognition, the activation of phagocytosis and, ultimately, the degradation of the cell corpse. As discussed, the multistep process from cell death to cell clearance is delicate, with multiple points of redundancy"

Comment: My bold is God's recognition of probable molecular failures. Definitely not intended or planned by God on purpose. Very carefully designed.

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