Biological complexity:photosynthesis new research (Introduction)

by David Turell , Thursday, July 27, 2017, 20:00 (2457 days ago) @ David Turell

The origin of photosynthesis and how it works has been newly studied:

https://phys.org/news/2017-07-picture-emerges-photosynthesis-sun-loving-bacteria.html

"'Nature's invention of photosynthesis is the single most important energy conversion process driving the biosphere, and photosynthesis forever changed the Earth's atmosphere,"

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"More than 3 billion years ago our planet had an atmosphere without oxygen. At this time, nature figured out a way to capture the sunlight and convert it food to take advantage of this everlasting energy source.

"Now, a research group led by Fromme has gained important new insights by resolving with near-atomic clarity, the very first core membrane protein structure in the simplest known photosynthetic bacterium, called Heliobacterium modesticaldum (Helios was the Greek sun god).

"By solving the heart of photosynthesis in this sun-loving, soil-dwelling bacterium, Fromme's research team has gained a fundamental new understanding of the early evolution of photosynthesis, and how this vital process differs between plants systems.

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"At the heart of photosynthesis is a reaction center; it's an elaborate complex of pigments and proteins that turn light into electrons to power the cell.

"Chlorophyll is the pigment that makes plants green. In plants, chlorophyll captures the sun's energy and uses it to make sugars out of carbon dioxide from the air and water.
Oxygenic photosynthesis in higher plants, green algae and cyanobacteria make use of Photosystem I (PSI), which is a Type I RC, and Photosystem II (PSII), which is a Type II RC.

"These work together to extract electrons from water to ferredoxin and finally reduce an energy carrier NADP+ to NADPH.

"In contrast, anoxygenic phototrophic bacteria, such as Heliobacterium modesticaldum, use a single RC to drive a cyclic electron transfer (ET) pathway that creates a proton-motive force across the membrane, which is used to drive energy production and metabolism by ATP synthesis.

"The reaction centers enclose these participants like a cage to efficiently capture all the available energy and photons of light by bringing all the elements together in the same vicinity.

"Reaction centers (RC) come in two main flavors of cofactors: iron (Type I) or quinone (Type II).

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"The heliobacteria RC has been proposed to be the closest thing alive to the earliest common ancestor of all photosynthetic reaction centers, when, around 3 billion years ago, the early Earth contained sulfur rich seas and little oxygen.

"But successfully purifying an RC protein and growing crystals needed for X-ray experiments can be a lengthy, difficult process.

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"They found an almost perfect symmetry in the heliobacter RC.

First, the amino acid composition of a pair of proteins was identical, called a homodimer.
This was the very first time that a RC was found to contain just a single pair of protein homodimers to drive photosynthesis.

"Finally, they mapped about 60 chlorophylls onto the RC protein complex, which was finally a way higher number than his colleague John Golbeck from Pennstate University who was part of the study predicted.

"The core polypeptide dimer and two small subunits coordinate 54 (bacterio)chlorophylls and 2 carotenoids that capture and transfer energy to the core at the reaction center, which performs charge separation, stabilization and electron transfer it consists of 6 (bacterio)chlorophylls and an iron-sulfur cluster; unlike other reaction centers, it lacks a bound quinone.

"Thus, the structure supports the hypothesis that electron transport in the HbRC does not require an intermediate cofactor.

"'High-resolution structures have been obtained from multiple heterodimeric (more than one protein) RCs (Purple bacteria RC, PSI, and PSII), but no homodimeric RC structure have been solved until now," said Fromme.

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"In evolutionary terms, this means that the heliobacteria RC may have first come from a single gene."

Comment: Without the production of oxygen, advanced life would not be here. This highly complex process did not appear by chance.