How does the photosynthesis reaction take place?
The essence of photosynthesis is that the energy of visible light is converted into
In other words, with the help of the energy of light, the bodyIt takes electrons off the molecule and transfers them to carbon dioxide molecules, restoring them and turning them into molecules of organic matter, which can then be oxidized again, gaining energy.
The whole system of plant photosynthesis reactions in one scheme: 6СО2 + 6H2O = glucose (С6H12О6) + 6О2
One of the key stages of this complex andmultistage process - binding of carbon dioxide. When this happens, carbon dioxide is attached to a compound called ribulose (1,5) bisphosphate, a sugar with two phosphate groups.
And the enzyme directs this reaction - ribulose bisphosphate carboxylase, or Rubisco (RuBisCO).
RuBisCO is an enzyme that is an absolutely complex of 16 protein chains at once. Most enzymes catalyze thousands of chemical transformations every second.
However, Rubisco only handles 3 to 10carbon dioxide molecules, depending on conditions. Such a low quality of the enzyme can only be compensated for by its quantity: by weight, it accounts for up to 30% of all water-soluble plant proteins, which makes it the most abundant protein on the planet.
Chloroplasts in leaf cells
Types of photosynthesis
Living organisms have two types of pigments that can act as photosynthetic receivers (antennas).
In the vast majority of organisms, the role of antennaschlorophylls play; less common is the case in which the vitamin A derivative retinal serves as an antenna. In accordance with this, chlorophyll and chlorophyll-free photosynthesis are distinguished.
- Chlorophyll-free photosynthesis
The chlorophyll-free photosynthesis system is differentsignificant simplicity of organization, in connection with which it is assumed evolutionarily to be the primary mechanism for storing the energy of electromagnetic radiation. The efficiency of chlorophyll-free photosynthesis as a mechanism for energy conversion is relatively low (only one H + is transferred per absorbed quantum).
- Chlorophyll photosynthesis
Chlorophyll photosynthesis is different frombacteriorhodopsin with significantly higher energy storage efficiency. At least one H + is transferred to each effectively absorbed quantum of radiation against the gradient.
Anoxygenic (or anoxic) photosynthesis occurs without oxygen evolution. Purple and green bacteria, as well as heliobacteria, are capable of anoxygenic photosynthesis.
Oxygenic or oxygenic photosynthesisaccompanied by the release of oxygen as a by-product. In oxygenic photosynthesis, non-cyclic electron transport occurs, although under certain physiological conditions, only cyclic electron transport occurs. An extremely weak electron donor, water, is used as an electron donor in a non-cyclic flow.
Hunger in agriculture
The population of the Earth, despite the second demographic transition, is constantly growing. If we could, at will, increase fertility in proportion to population growth, there would be no big problem.
However, today a person has mastered about a thirdsuitable for agriculture land. Almost all suitable territories in South Asia, in the Middle East and North America have already been plowed up, and the development of the remaining areas threatens us with erosion.
The place on the planet may simply run out, so we need to find new ways to increase food production. This has already been done before.
The last time this happened was due to the "greenrevolution "50-70-ies of the last century. Then, the breeding of new high-yielding varieties of cereals, the introduction of pesticides and advanced irrigation systems made it possible to dramatically - almost twice - increase the yield.
How to speed up photosynthesis
The cornerstone of this problem is rubisco, the enzyme we've already talked about.
However, it turned out to be not so easy. Targeted mutagenesis of individual amino acid residues did not lead to any noticeable results.
Also, the method of direct evolution was applied to it.enzymes: it creates a huge collection of Rubisco gene variants by random mutations. All this variety was applied on E. coli - Escherichia coli... Using this approach, the researchers were able to increase the activity of Rubisco cyanobacteria, which works perfectly in E. coli cells.
But the same method didn't work with plants.In addition, this enzyme is assembled from parts of two different "manufacturers": the genes encoding Rubisco chains are found not only in the cell nucleus, but also in the chloroplast genome, which complicates manipulation with them. Researchers have to work with two genomes at once, using different techniques of gene modification.
But the scientists did not give up on this.They came up with a new idea: to increase the amount of rubisco, since the leaves of the plants are literally filled with it. For this, the authors used GMO methods. However, Rubisco's overexpression of genes alone was not enough - something else was missing to assemble the enzyme.
Over the years, it turned out that in the assemblyRubisco takes part at once several protein-packers - RAF1 and RAF2 (RuBisCO Assembly Factor). These folding proteins (called chaperones) tend to stabilize the harvested protein chain during assembly, giving it time to fold properly.
This was the problem of previous works:Rubisco's genes really actively synthesized protein "building blocks" of the enzyme, but the lack of chaperones did not allow the collection of a sufficient amount of Rubisco from semi-finished polypeptide chains. The number of chaperones also needed to be increased.
Therefore, the authors took these conditions into account and, as a result, the total rubisco content in the leaves of transgenic maize increased by 30%.
Because of this, not all of the additional enzyme is at allbecame involved in the process of photosynthesis. However, in spite of everything, the final fixation of carbon dioxide grew 15% anyway, this significantly accelerated the growth of GM corn.
As a result of a study by Chinese scientists in 2020, it was possible to accelerate the photosynthesis of algae and a flower. Scientists accelerate photosynthesis of green algae Chlorella pyrenoidosa and higher plant Arabidopsis thaliana using a light-harvesting polymer. The polymer increased their activity of photosynthetic systems due to electrostatic and hydrophobic binding to the walls of photosynthetic cells.
According to the authors, thanks to the good abilityto absorb green light, water solubility and biocompatibility, these synthetic polymers are potentially suitable for use in the production of biofuels, as well as energy and environmental development.
Currently, photovoltaic cells,acting in an aqueous environment, they are efficient, but clearly imperfect. Artificial photosynthesis is still quite effective as a tool for binding atmospheric carbon, and at the same time produces a stable flow of charged particles (protons and electrons).
Thus, photosynthetic cells could be combined with solar panels - for example, already installed on the roofs of private houses in the United States.
The solar panel could give someenergy received for electrolysis. In this case, photovoltaic cells connected to it would participate in binding carbon dioxide and splitting water to produce hydrogen, which, in turn, is an environmentally friendly fuel.
Development of catalysts for such processeswould allow not to be limited to the reproduction of ordinary photosynthesis, but to synthesize, for example, proteins or enzymes. We have already learned how to scale solar cells, so we could scale photovoltaic cells with them.
Also, such technologies could contribute to the decomposition of toxic waste or plastic, yielding hydrogen and energy as an output.
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