Natures wonders: when photosynthesis started (Introduction)

by David Turell , Saturday, May 15, 2021, 20:46 (1286 days ago) @ David Turell

A new study describes the early process:

https://phys.org/news/2021-05-path-photosynthesis.html

"Heliobacteria, a type of bacteria that uses photosynthesis to generate energy, has reaction centers thought to be similar to those of the common ancestors for all photosynthetic organisms. Now, a University of Michigan team has determined the first steps in converting light into energy for this bacterium.

"'Our study highlights the different ways in which nature has made use of the basic reaction center architecture that emerged over 3 billion years ago," said lead author and U-M physicist Jennifer Ogilvie. "We want to ultimately understand how energy moves through the system and ends up creating what we call the 'charge-separated state.' This state is the battery that drives the engine of photosynthesis."

"Photosynthetic organisms contain "antenna" proteins that are packed with pigment molecules to harvest photons. The collected energy is then directed to "reaction centers" that power the initial steps that convert light energy into food for the organism. These initial steps happen on incredibly fast timescales—femtoseconds, or one millionth of one billionth of a second. During the blink of an eye, this conversion happens many quadrillions of times.

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"When light hits a photosynthetic organism, pigments within the antenna gather photons and direct the energy toward the reaction center. In the reaction center, the energy bumps an electron to a higher energy level, from which it moves to a new location, leaving behind a positive charge. This is called a charge separation. This process happens differently based on the structure of the reaction center in which it occurs.

"In the reaction centers of plants and most photosynthetic organisms, the pigments that orchestrate charge separation absorb similar colors of light, making it difficult to visualize charge separation. Using the heliobacteria, the researchers identified which pigments initially donate the electron after they're excited by a photon, and which pigments accept the electron.

"Heliobacteria is a good model to examine, Ogilvie said, because their reaction centers have a mixture of chlorophyll and bacteriochlorophyll, which means that these different pigments absorb different colors of lights. For example, she said, imagine trying to follow a person in a crowd—but everyone is wearing blue jackets, you're watching from a distance and you can only take snapshots of the person moving through the crowd.

"'But if the person you were watching was wearing a red jacket, you could follow them much more easily. This system is kind of like that: It has distinct markers," said Ogilvie, professor of physics, biophysics, and macromolecular science and engineering.

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"To probe reaction centers in heliobacteria, Ogilvie's team uses a type of ultrafast spectroscopy called multidimensional electronic spectroscopy, implemented in Ogilvie's lab by lead author and postdoctoral fellow Yin Song. The team aims a sequence of carefully timed, very short laser pulses at a sample of bacteria. The shorter the laser pulse, the broader light spectrum it can excite.

"Each time the laser pulse hits the sample, the light excites the reaction centers within. The researchers vary the time delay between the pulses, and then record how each of those pulses interacts with the sample. When pulses hit the sample, its electrons are excited to a higher energy level. The pigments in the sample absorb specific wavelengths of light from the laser—specific colors—and the colors that are absorbed give the researchers information about the energy level structure of the system and how energy flows through it."

Comment: This study picks apart another aspect of the photosynthetic process. I've previously presented quantum processes as part of the mechanism. Without this process there would not be enough oxygen for complex life.