Category Archives: Symmetry

Conceptual Links Between Respiration and Photosynthesis

Let’s consider some conceptual links between the processes of aerobic respiration and photosynthesis.

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Electron transport: Front-loading and More

We’ve seen that the cytochrome oxidase, otherwise known as haem-copper oxygen reductase, plays the key role in aerobic respiration. There are actually three different versions of these protein complexes, known as type A, B, and C. The type A version is the one that is found in our mitochondria.

Researchers from France recently took a close look at these oxidases, surveying 673 complete genomes from both the archaeal and bacterial domains (Brochier-Armanet C, Talla E, Gribaldo S. 2009. The multiple evolutionary histories of dioxygen reductases: Implications for the origin and evolution of aerobic respiration. Mol Biol Evol. 26:285-97). They retrieved 1,640 examples, which indicates that many prokaryotes carry multiple versions of these oxidases.

Through careful genomic analyses, the researchers were able to track the evolutionary history of these three types of oxidases.

They found that type B oxidases likely originated among the archaebacteria and some copies have been laterally transferred to bacteria. Type C oxidases likely originated among the proteobacteria and transferred to other types of bacteria. But what about the type A oxidases, the type that are found in eukaryotic mitochondria (which are themselves the product of an earlier endosymbiosis)?

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Feel the Symmetry

What is really cool is how so much of our biosphere, especially aspects crucial to human life, are built around two hugely important symmetrical reactions: