In the Light of Evolution Volume IV: The Human Condition (2010) / Chapter Skim
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7 Bioenergetics, the Origins of Complexity, and the Ascent of Man-Douglas C. Wallace
7 Bioenergetics, the Origins of Complexity, and the Ascent of Man-Douglas C. Wallace
Pages 127-146
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From page 127... ...
structures embody information, and biological information is stored in nucleic acids. The progressive increase in biological complexity over geo logic time is thus the consequence of the information-generating power of energy flow plus the information-accumulating capacity of DnA, winnowed by natural selection.
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From page 128... ...
Therefore, biological complexity increases because a portion of the information generated by energy flow through each generation is added to the accumulated information stores from previous generations. The increasingly complex information can then be used to recreate the more complex structures, as long as there is sufficient energy flow (Mathematical Formulations)
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From page 129... ...
. Therefore, it is the information-generating power of energy flux plus the information storage capacity of nucleic acids, winnowed by natural selection, that continually drives biology to increased complexity.
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From page 130... ...
Thus, adaptive bioenergetic mtDnA mutations arise in populations within hundreds to thousands of years and permit rapid physiological adaptation to changes in the regional energy environment. As regional subpopulations become established, additional nDnA mutations in bioenergetic genes arise to further solidify the physi
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From page 131... ...
Because growth and reproduction must be coordinated with the availability of energy, the status of the energetic flux through the cellular bioenergetic systems, particularly the mitochondrion, came to be communicated to the nucleus-cytosol by alterations in the nDnA chromatin, the epigenome, and cytosol signal transduction systems, based on the production and availability of high-energy intermediates, reducing equivalents, and ros produced primarily by the mitochondrion. As a consequence, biological systems interface with the energy environment at three levels: the species level in which nDnA gene variation alters anatomical forms to exploit different environmental energy reservoirs, the species population level in which primarily mtDnA bioenergetic genetic variation permits adaptation to long-term regional differences in the niche energetic environment, and the individual level in which high-energy intermediates reflecting cyclic changes in environmental energetics drive the modification of the epigenome and the signal transduction pathways.
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From page 132... ...
These are achieved through epigenomic changes: modification of DnA by methylation or of histones through phosphorylation, acetylation, and methylation. shorter-term reversible changes are accomplished through modulation of transcription factors and alterations in signal transduction pathways.
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From page 133... ...
. The mtDnA genes of all animals encode the core proteins of oXPhos, so mtDnA mutations directly affect bioenergetic physiology and provide the ideal genetic system for adaptation to changes in regional energy environments.
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From page 134... ...
and then through complex iii, cytochrome c, and complex iv to reduce 1/2 o2 into h2o. The energy that is released as the electrons pass through complexes i, iii, and iv is used to transport protons out across the mitochondrial inner membrane to generate a transinner membrane electrochemical potential (ΔP = Δψ + Δμh+)
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From page 135... ...
The percentage of mutant and normal mtDnAs can be unequally distributed at cytokinesis, such that the percentage of mutant mtDnAs can drift during successive mitotic and meiotic cell divisions, replicative segregation. As the percentage of deleterious mtDnA mutations increases, the energy output of the cell declines until it drops below the minimum energy output required for that cell type to function and symptoms ensue, the bioenergetic threshold.
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From page 136... ...
. Although mild mtDnA mutations may be adaptive in one local energy environment, the same mutation might be maladaptive in another energy environment.
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From page 137... ...
ENERGY FLUCTUATION AND CYCLIC ADAPTATION individual adjustments to cyclic changes in the energy environment must be reversible. Therefore, cyclic changes cannot be due to DnA sequence changes, but must be due to changes in bioenergetic gene expression.
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From page 138... ...
. evidence that the epigenome regulates bioenergetics comes from the facts that pathogenic mtDnA mutations result in symptoms similar to those attributed to the epigenomic disease and that several epig enomic diseases have been associated with mitochondrial dysfunction.
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From page 139... ...
. Bioenergetic Regulation of Signal Transduction and Metabolism To respond to more rapid energy environment fluctuations, animal cells modify transcription factors and signal transduction systems via high-energy intermediates.
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From page 140... ...
in the mitochondrion, a substantial portion of the nADh is oxidized via the eTC using o2 to generate ΔP, but the redox state of a portion of the nADh + h+ is increased by the nicotinamide nucleoside transhydrogenase (nnt) , using energy from ΔP to drive the transfer of reducing equivalents from nADh + h+ to nADPh + h+ with a redox potential of −405 mv.
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From page 141... ...
Trx1(sh) 2/ss donates reducing equivalents to cytosolic peroxidoxins to control radicals, and to the thiol/disulfides of enzymes and transcription factors to regulate their activity.
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From page 142... ...
The discovery that the mammalian ovary harbors a selective system to eliminate the most deleterious mtDnA mutations explains why the high mtDnA mutation rate does not drive mammalian populations to extinction from overwhelming mtDnA genetic load. since the mtDnA only encodes oXPhos genes and oXPhos genes are expressed in every cell of the body, intraovarian selection can monitor the physiological con sequences of mitochondrial oXPhos defects within proto-oocytes and eliminate those with the most severe bioenergetic aberrations.
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From page 143... ...
Genetic load then places an upper limit on the combination of the nDnA mutation rate and the genetic target size, the amount of protein coding information in the organism's genome. in animal species, a steady state may have been achieved between nDnA mutation rate and gene target size when the genome complexity reached that of the invertebrates.
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From page 144... ...
as ΔA declines, provided αU is constant. however, in a system where energy flows through the system, such that an equal quantity of energy enters and leaves the system, the total instantaneous energy (U)
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From page 145... ...
, divided by the sum of the energy flux through the biosphere over the past 3.5 billion years, represents the average efficiency by which energy flux has been converted into conserved biological information on earth. ACKNOWLEDGMENTS This work was supported by national institutes of health Grants ns21328, AG24373, DK73691, AG13154, and AG16573; California institute for regenerative Medicine Comprehensive Grant rC1-00353-1; and a Doris Duke Clinical interfaces Award 2005.
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