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Free radicals as respiratory distress signal


corybroo
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I’ve been reading The Vital Question, a book by Nick Lane that explores the role of energy in the origin of life from alkaline hydrothermal vent to eukaryotes.  (There’s a 2 ½ minute video by the author on the linked page if you want a super quick summary.)  In the last chapter, he looks at the free-radical theory and tries to explain why “Taking high-dose antioxidant supplements carries a modest but consistent risk.”  It has been shown that blocking free-radical signals with antioxidants can block ATP synthesis in cell cultures.  It is likely that free-radical signals optimize respiration in mitochondria by increasing the number of respiratory complexes which increases respiratory capacity which leads to more ATP.  Antioxidants suppress the trigger of this mitochondrial biogenesis causing the increase in free radicals to be ignored by the cell.  He proposes a “death limit” of free radicals above which the cell commits apoptosis.

“Free radicals signal the problem that respiratory capacity is low, relative to demand.  If the problem can be fixed by making more respiratory complexes, raising respiratory capacity, then all is well and good.  If that does not fix the problem, the cell kills itself, removing the presumably defective [mitochondrial] DNA from the mix.”

A subsequent paragraph states that there is no simple relationship between rate of living and free-radical leak:

“When you exercise, you consume more oxygen, so your free-radical leak rises, right?  Wrong.  It remains similar or even goes down because the proportion of radicals leaked relative to oxygen consumed falls off considerably.”

That is summarized in a diagram labeled Why rest is bad for you.

    

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