Biological complexity: mitochondrial structure found (Introduction)

by David Turell , Friday, September 22, 2017, 18:56 (2619 days ago) @ David Turell

Take a look at this story. The complexity of the molecules is amazing:

https://phys.org/news/2017-09-mitochondrial-respiratory-supercomplex-decoded.html

"The picture of the megacomplex (MC) that has emerged has the following stoichiometry: MCI2II2III2IV2. This means that complexes I,II,III,& IV are each present in duplicate while complex V is absent. It is configured within the membrane into a circular structure with the dimeric CIII located at the center and fed by peripheral CI and CIV complexes. The CII complexes are apparently not essential requirements to the core structure but rather are theorized to be wedged into gaps as needed. The authors also found evidence for a lightweight rendition of the megacomplex that can sometimes be assembled with just a single CI complex.

"The central positioning of the CIV dimer suggests a certain logic. CIV, or cytochrome oxidase, is the terminal resting ground for electrons entering the chain. Those that make it this far have been lowered down the reduction potential hierarchy as far as they can go. Here, they are sunk into waiting oxygen molecules, which are then exhausted as molecules of water. High potential electrons packaged as NADH enter the complex at its perimeter and are funneled into the center. The absence of C5 complexes may not be so unusual, considering that they are typically found as rows of "V'-shaped dimers that contort the membrane into regions of high curvature at bends in the cristea.

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"The central positioning of the CIV dimer suggests a certain logic. CIV, or cytochrome oxidase, is the terminal resting ground for electrons entering the chain. Those that make it this far have been lowered down the reduction potential hierarchy as far as they can go. Here, they are sunk into waiting oxygen molecules, which are then exhausted as molecules of water. High potential electrons packaged as NADH enter the complex at its perimeter and are funneled into the center. The absence of C5 complexes may not be so unusual, considering that they are typically found as rows of "V'-shaped dimers that contort the membrane into regions of high curvature at bends in the cristea.

"With the basic structure in hand, the researchers were able to suggest a few basic principles of operation. Their inclusion and placement of CII effectively explains reverse electron transport from succinate to NADH. The proposed geometry also creates a sealed Q-pool (a lipid-soluble electron carrier) which is accessible to both CI and CII. The authors were also able to pinpoint the identity and locations of several lipid molecules that secure the complex within the membrane, specifically, several pivotal several lipid molecules that secure the complex within the membrane, specifically, several pivotal molecules of phosphatidylethanolamine, phosphatidylcholine, and cardiolipin. They were also able to identify preferred or most efficient electron transfer pathways, which in turn constrain how many electrons can simultaneously be transferred among active carriers."

Comment: this is a highly complex article based on an extraordinary piece of research. I've presented it to show the complexity of mitochondria, the size of enzymatic molecules an evolutionary process is supposed to find by chance. Never!