The fermentation (glycolysis) of glucose with release of carbon dioxide generates only two net molecules of ATP, whereas complete oxidation of glucose to water generates 12-fold more molecules of ATP. In anaerobic conditions the final electron acceptor can be sulfur or sulfate, but with the advent of an O2 gas-containing atmosphere on the Earth’s surface and waters, life adapted to use the highly electronegative O2 molecule as the final electron acceptor. This process relies on the chemiosmotic mechanism whereby electrons are transferred through reducing equivalents, for example, NADH, using mobile, lipid permeable quinones as intermediate charge carriers, while protons are pumped across an ion impermeable membrane using the energy of the Sun or substrates to establish a voltage (electro-)-chemical gradient. In turn, most ATP is generated when the protons reenter down this gradient. This transduction process was crucial for life to develop. The oxidation phosphorylation machinery existed in prokaryotes long before the tricarboxylic cycle and electron transport system became incorporated entirely from a prokaryote to another as an endosymbiont. The encapsulated, two-membrane endosymbiont is now called the mitochondrion, and its evolution is likely tied to encapsulation of a prokaryote’s genome into another’s, forming a defined nucleus within the first eukaryotes. Most of the endosymbiont’s mitochondrial genome was transferred to the host nucleus or eliminated, while the host DNA now furnishes over 1000 nuclear-encoded proteins to assure efficient function and regulation of its mitochondria. Mitochondria exhibit great diversity within a tissue or organism (heterogeneity). They are very flexible in regulating energy output according to needs, for example, running or flying, and in adjusting to cell environmental changes, for example, ischemic stress. Modern-day cardiac myocyte mitochondria are exemplified here as high-energy mitochondria. Before the last common ancestor, the first proteins were made to facilitate the work of the ribozyme in precisely coding peptides with information stored in RNA after transcription from DNA. This required adaption of a final standard genetic code by which only four DNA nucleobases, arranged in a linear codon of only three nucleobases, encode only one amino acid out of the 20 amino acids utilized in lifeforms. The genetic code exhibits redundancy in the last base of the codon but coding is not ambiguous as a given codon only translates one distinct amino acid. Protein function is dependent not only on the linear sequence of amino acids but also on the folding of the protein by hydrogen bonding among the amino acids and water in the cytoplasm. Viruses likely coexisted with early prokaryote genomes.

Genesis of Mitochondria to Power Complex Lifeforms

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发表日期：

2025年

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David F. Stowe

摘要

The fermentation (glycolysis) of glucose with release of carbon dioxide generates only two net molecules of ATP, whereas complete oxidation of glucose to water generates 12-fold more molecules of ATP. In anaerobic conditions the final electron acceptor can be sulfur or sulfate, but with the advent of an O2 gas-containing atmosphere on the Earth’s surface and waters, life adapted to use the highly electronegative O2 molecule as the final electron acceptor. This process relies on the chemiosmotic mechanism whereby electrons are transferred through reducing equivalents, for example, NADH, using mobile, lipid permeable quinones as intermediate charge carriers, while protons are pumped across an ion impermeable membrane using the energy of the Sun or substrates to establish a voltage (electro-)-chemical gradient. In turn, most ATP is generated when the protons reenter down this gradient. This transduction process was crucial for life to develop. The oxidation phosphorylation machinery existed in prokaryotes long before the tricarboxylic cycle and electron transport system became incorporated entirely from a prokaryote to another as an endosymbiont. The encapsulated, two-membrane endosymbiont is now called the mitochondrion, and its evolution is likely tied to encapsulation of a prokaryote’s genome into another’s, forming a defined nucleus within the first eukaryotes. Most of the endosymbiont’s mitochondrial genome was transferred to the host nucleus or eliminated, while the host DNA now furnishes over 1000 nuclear-encoded proteins to assure efficient function and regulation of its mitochondria. Mitochondria exhibit great diversity within a tissue or organism (heterogeneity). They are very flexible in regulating energy output according to needs, for example, running or flying, and in adjusting to cell environmental changes, for example, ischemic stress. Modern-day cardiac myocyte mitochondria are exemplified here as high-energy mitochondria. Before the last common ancestor, the first proteins were made to facilitate the work of the ribozyme in precisely coding peptides with information stored in RNA after transcription from DNA. This required adaption of a final standard genetic code by which only four DNA nucleobases, arranged in a linear codon of only three nucleobases, encode only one amino acid out of the 20 amino acids utilized in lifeforms. The genetic code exhibits redundancy in the last base of the codon but coding is not ambiguous as a given codon only translates one distinct amino acid. Protein function is dependent not only on the linear sequence of amino acids but also on the folding of the protein by hydrogen bonding among the amino acids and water in the cytoplasm. Viruses likely coexisted with early prokaryote genomes.