General equation of photosynthesis reaction. General Plant Photosynthesis Equation

Photosynthesis - This is a combination of the synthesis of organic compounds from inorganic due to the transformation of light energy into the energy of chemical bonds. Green plants are belonging to phototrophic organisms, some prokaryotes - cyanobacteria, purple and green serobacteria, vegetable flagella.

Studies of the photosynthesis process began in the second half of the XVIII century. An important discovery made an outstanding Russian scientist K. A. Timiryazev, who substantiated the doctrine of the cosmic role of green plants. Plants absorb the sun's rays and convert light energy into the energy of chemical bonds synthesized with organic compounds. Thus, they ensure the preservation and development of life on Earth. The scientist also theoretically substantiated and experimentally proved the role of chlorophyll in light absorption in the process of photosynthesis.

Chlorophylls are essential of photosynthetic pigments. In structure, they are similar to hemoglobin gem, but instead of iron contain magnesium. The iron content is necessary to ensure the synthesis of chlorophyll molecules. There are several chlorophylls that are distinguished by their chemical structure. Mandatory for all phototrofs is chlorophyll A. . Chlorophyllb. occurs in green plants, chlorophyll S. - at diatoms and brown algae. Chlorophyll D. Characterized for red algae.

Green and purple photosynthetic bacteria have special bacterioculorophylls . Photosynthesis of bacteria has a lot in common with photosynthesis of plants. It is distinguished by the fact that the bacteria donor hydrogen is hydrogen sulfide, and in plants - water. Green and purple bacteria does not have a photose system II. Bacterial photosynthesis is not accompanied by the release of oxygen. Total bacterial photosynthesis equation:

6C0 2 + 12H 2 S → C 6 H 12 O 6 + 12S + 6H 2 0.

At the heart of photosynthesis is the redox process. It is associated with the transfer of electrons from connections-suppliers of electrons-donors to compounds that are perceived by acceptors. Light energy turns into the energy of synthesized organic compounds (carbohydrates).

On the membranes of chloroplasts there are special structures - reaction centers which contain chlorophyll. Green plants and cyanobacteria distinguish two photosystems – first (I) and second (II) which have different reaction centers and are interconnected through the electron transfer system.

Two phases of photosynthesis

The process of photosynthesis of two phases is consisting: light and dark.

It occurs only in the presence of light on the internal membranes of mitochondria in the membranes of special structures - tylakoids . Photosynthetic pigments capture light quanta (photons). This leads to an "excitation" of one of the electrons of the chlorophyll molecule. With the help of molecules, the electron is moving to the outer surface of the thylacoid membrane, acquiring certain potential energy.

This electron B. photosystem I. May return to its energy level and restore it. NCTF (nicotinydadenindinucleotid phosphate) may also be transmitted. Interacting with hydrogen ions, electrons restore this compound. Restored NADF (NADPH) supplies hydrogen to restore atmospheric C0 2 to glucose.

Such processes occur in photosystem II. . Excited electrons can be transmitted to the photo system I and restore it. Restoration of the photosystem II occurs due to electrons that supply water molecules. Water molecules are split (photoliz of water) On hydrogen protons and molecular oxygen, which is released into the atmosphere. Electrons are used to restore the photosystem II. Football equation of water:

2H 2 0 → 4N + + 0 2 + 2e.

When electron returns from the outer surface of the thylacoid membrane to the previous energy level, energy is distinguished. It is covered in the form of chemical bonds of ATP molecules, which are synthesized during reactions in both photosystems. The process of synthesis of ATP with ADP and phosphoric acid is called photo phosphaeling . Some of the energy is used to evaporate water.

During the light phase of photosynthesis, the rich compounds are formed: ATP and NADF N. When decaying (photolidium), water molecular oxygen is released into the atmosphere of water to the atmosphere.

Reactions proceed in the inner medium of chloroplasts. They can occur both in the presence of light and without it. Organic substances are synthesized (C0 2 is restored to glucose) using energy that was formed in the light phase.

The process of restoration of carbon dioxide is cyclical and called calvin cycle . Named in honor of the American researcher M. Calvin, who discovered this cyclic process.

A cycle begins with a reaction of atmospheric carbon dioxide with ribulosecophosphate. Catalyzes the enzyme process carboxylase . Ribulseobiphosphate is a five-carbon sugar, connected to two phosphoric acid residues. A number of chemical transformations occur, each of which catalyzes its specific enzyme. As the final product of photosynthesis forms glucose and also restores ribulosecophosphate.

The total equation of the photosynthesis process:

6C0 2 + 6N 2 0 → C 6H 12 O 6 + 60 2

Thanks to the process of photosynthesis, the light energy of the Sun is absorbed and it is converted into the energy of chemical bonds of synthesized carbohydrates. By supply chains, energy is transmitted by heterotrophic organisms. In the process of photosynthesis, carbon dioxide is absorbed and oxygen is distinguished. All atmospheric oxygen has photosynthetic origin. Over 200 billion tons of free oxygen stands out annually. Oxygen protects life on Earth from ultraviolet radiation, creating an ozone atmosphere screen.

The process of photosynthesis is ineffective, since only 1-2% of solar energy is translated into the synthesized organic matter. This is due to the fact that plants do not absorb light enough, part of it is absorbed by the atmosphere, etc. Most of the sunlight is reflected from the surface of the earth back into space.

Organic (and inorganic) compounds.

The process of photosynthesis is expressed by the total equation:

6So 2 + 6N 2 O ® C 6 H 12 O 6 + 6O 2.

Original substances are formed in a green plant from extremely oxidized substances - organic substances, and molecular oxygen is highly born. In the process of photosynthesis, not only CO 2 is restored, but also nitrates or sulfates, and energy can be directed to various endergonic processes, including transport substances.

The general photosynthesis equation can be represented as:

12 H 2 O → 12 [H 2] + 6 O 2 (light reaction)

6 CO 2 + 12 [H 2] → C 6 H 12 O 6 + 6 H 2 O (dark reaction)

6 CO 2 + 12 H 2 O → C 6 H 12 O 6 + 6N 2 O + 6 O 2

or per 1 mol from 2:

CO 2 + N 2 OH 2 O + O 2

All oxygen released during photosynthesis is made of water. The water in the right part of the equation is not subject to reduction, since its oxygen comes from CO 2. The methods of labeled atoms it was obtained that H 2 o in chloroplasts is heterogeneous and consists of water coming from the external environment and water formed during photosynthesis. In the process of photosynthesis, both types of water are used.

Proof of education O 2 in the process of photosynthesis is the work of the Dutch microbiologist Wang Nile, who studied bacterial photosynthesis, and came to the conclusion that the primary photochemical reaction of photosynthesis consists in dissociation H 2 O, and not decomposition of CO 2. Capable to photosynthetic assimilation CO 2 bacteria (except cyanobacteria) are used as reducing agents H 2 S, H 2, CH 3 and others, and do not allocate 2.

This type of photosynthesis is called photoreduction:

CO 2 + H 2 S → [CH 2 O] + H 2 O + S 2 or

CO 2 + H 2 A → [CH 2 O] + H 2 O + 2A,

where H 2 A is oxidizes the substrate, the donor of hydrogen (at higher plants is H 2 O), and 2a is about 2. Then the primary photochemical act in the photosynthesis of plants should be the decomposition of water into the oxidizing agent [OH] and the reducing agent [H]. [H] Restores CO 2, and [he] participates in the reactions of release on 2 and the formation of H 2 O.

Solar energy with the participation of green plants and photosynthesising bacteria is converted into the free energy of organic compounds.

To carry out this unique process during evolution, a pho-toosyntic apparatus was created, comprising:

I) a set of photoactive pigments capable of absorbing electromagnetic radiation of certain spectrum areas and store this energy in the form of electronic excitation energy, and

2) Special apparatus of electronic excitation energy conversion in different shapes of chemical energy.

First of all, it redox-energy , Communication with the formation of high-screen compounds, energy of electrochemical potential due to the formation of electrical and pro-ton gradients on the mating membrane (Δμ H +), the Energy of Phosphate Savory ATP and other macroeergic compounds, which is then converted into the free energy of organic molecules.

All these types of chemical energy can be used in the process of visibility for absorption and transmembrane ion transfer and in most metabolic reactions, i.e. In constructive exchange.

The ability to use solar energy and introduce it into biosphere processes and determines the "cosmic" role of green plants, which the Great Russian physiologist K.A. wrote Timiryazev.

The process of photosynthesis is a very complex system for a simple and temporary organization. The use of high-speed impulse analysis methods made it possible to establish that the photosynth-for process includes various in the reaction rate - from 10 -15 s (in the femtosecond time interval, the processes of absorption and migration of energy) up to 10 4 s (formation of photosynthesis products). The photosynthetic apparatus includes a structure with dimensions from 10 -27 m 3 at a low molecular level up to 10 5 m 3 at the level of crops.

Circuit diagram of photosynthesis.

The entire complex complex of reactions co-setting the photosynthesis process can be submitted as a schematic diagram in which the main stages of photosynthesis and their essence are displayed. In the current scheme of photosynthesis, four stages can be distinguished, which differ in nature and reaction rates, as well as the value and essence of the processes occurring at each stage:

Stage I - physical. Includes photophysical in nature by the reaction of energy absorption by pigments (P), its intensity in the form of electron excitation energy (P *) and migration to the reaction center (RC). All reactions are extremely fast and occur at a speed of 10 -15 - 10 -9 s. The primary re-action of energy absorption is localized in light-cutting antenna composhexes (SSC).

Stage II - Photochemical. The reactions are localized in the reactionary centractions and flow at a speed of 10 -9 s. At this stage of photosynthesis, the energy of the electron excitation of the pigment (P (RC)) of the reaction center is used to divide charges. At the same time, an electron electron electron electron is transmitted to the primary acceptor A, and the resulting system with separated charges (P (RC) - a) contains a certain amount of energy already in chemical form. The oxidized pigment P (RC) restores its structure by oxidation of the donor (D).

The conversion of one type of energy in the reaction center in the reaction center is a central event of the photosynthesis process, which requires the stringent conditions of the structural organization of the system. Currently, molecular models of plant reaction centers and bacteria are mostly known. The similarity of the structural organization has been established, which is evidenced by the high degree of conservatism of the primary processes of photosynthesis.

The primary products formed on the photochemical stage (n *, a -) are very labils, and the electron can return to the oxidized pigment P * (the process of recombination) with useless energy loss. Therefore, the need is a quick further stabilization of educated reduced products with high energy potential, which is carried out on the following, III stages of photosynthesis.

III Stage - Electron Transport Reactions. The chain of carriers from the one-personal value of the redox potential (e n ) Exactly the so-called electron transport chain (ETC). Redox components ETC are organized in chloroplasts in the form of three main functional compets - photosystems I (FSI), photosystems II (FSII), cytochrome b 6 F.-Comp-lexa, which provides high electron flux speed and the possibility of its regulation. As a result of the work of the ETC, high-sector products are formed: reduced ferredoxin (PD EXT) and NAPFN, as well as rich in the energy of the ATP molecule, which are used in the dark recyclables of CO 2, constituting the IV stage of photosynthesis.

IV Stage - "Dark" absorption reactions and carbon dioxide recovery.The reactions pass to the formation of carbohydrates, the final products of photosynthes-for, in the form of which solar energy, absorbed and converted-bathroom in the "light" reactions of photosynthesis. The rate of "dark" enzymatic reactions - 10 -2 - 10 4 s.

Thus, the entire move of photosynthesis is carried out in the interaction of three dying-cords - energy flow, electrons flow and carbon flux. The pairing of three threads requires clear coordination and regulating the components of their reactions.

Equation: 6CO2 + 6N2O ----\u003e C6H12O6 + 6O2

Photosynthesis - the process of formation of organic matter from carbon dioxide and water in light with the participation of photosynthetic pigments (chlorophyll in plants, bacterioction and bacterioropacin in bacteria).

Photosynthesis is the main source of biological energy, photosynthetic autotrophs use it for the synthesis of organic substances from inorganic, heterotrophs exist due to energy stored by autotrophs in the form of chemical bonds, released it in breathing and fermentation processes. The energy obtained by humanity during the combustion of fossil fuels (coal, oil, natural gas, peat) is also stored in the process of photosynthesis.
Photosynthesis is the main entrance of inorganic carbon into the biological cycle. All free oxygen atmosphere - biogenic origin and is a by-product of photosynthesis. The formation of an oxidative atmosphere (oxygen catastrophe) completely changed the state of the earth's surface, made it possible to appear breathing, and in the future, after the formation of the ozone layer, made it possible to reach the land.

Bacterial photosynthesis

Some pigment-containing serobacteria (purple, green), containing specific pigments - bacteriochlorophylls, are able to absorb solar energy, with which hydrogen sulfide in their organisms split and gives hydrogen atoms to restore the corresponding compounds. This process has a lot in common with photosynthesis and is only distinguished by the fact that purple and green bacteria donor hydrogen is hydrogen sulfide (occasionally - carboxylic acids), and in green plants - water. For those and other cleavage and transfer of hydrogen due to the energy of the absorbed sunlight.

Such bacterial photosynthesis, which occurs without the release of oxygen, is called photoreduction. The photo generation of carbon dioxide is associated with the transfer of hydrogen not from water, but from hydrogen sulfide:

6SO 2 + 12N 2 S + HV → C6H 12 O 6 + 12S \u003d 6N 2 O

The biological importance of chemosynthesis and bacterial photosynthesis across the planet is relatively small. Only chemosynthetic bacteria play a significant role in the process of sulfur circulation in nature. Absorbing green plants in the form of salts of sulfuric acid, sulfur is restored and included in the composition of protein molecules. Next, in the destruction of dead vegetative and animal residues, sulfur with sulfide, which is oxidized by sulfide sulfide, which is oxidized by sulfur-free sulfur (or sulfuric acid), sulfite-free in soil. Chemo and photoauthotrophic bacteria are essential in the cycle of nitrogen and sulfur.

The process of converting the radiant energy of the Sun to the chemical using the latter in the synthesis of carbohydrate carbohydrates. This is the only way to capture solar energy and use it for life on our planet.

The capture and transformation of solar energy is carried out by multiple photosynthetic organisms (photoautotrophs). These include multicellular organisms (higher green plants and lower forms - green, brown and red algae) and unicellular (eurlen, dinoflagellates and diatoms of algae). A large group of photosynthetic organisms make up prokaryotes - blue-green algae, green and purple bacteria. Approximately half of the work on photosynthesis on Earth is carried out by the highest green plants, and the rest of half is mainly unicellular algae.

The first ideas about photosynthesis were formed in the 17th century. In the future, as new data appears, these submissions changed repeatedly [show] .

Development of ideas about photosynthesis

The beginning of the study of photosynthesis was laid in 1630, when Van Gelmont showed that the plants themselves form organic matter, and not get them out of the soil. Weighing the pot of the ground in which Iva grew up, and the tree itself, he showed that for 5 years the mass of the tree increased by 74 kg, while the soil lost only 57. Wang Helmont concluded that the rest of the food received the rest of the food Water that watered a tree. Now we know that the main material for the synthesis is the carbon dioxide extracted by a plant from the air.

In 1772, Joseph Priested showed that the bloss of mint "corrects" air, "spoiled" by a burning candle. Seven years later, Yang Ingenhuz found that plants can "correct" bad air only being in the light, and the ability of plants to "correct" the air is proportional to the clarity of the day and the duration of the remaining plants in the sun. In the dark, the plants allocate air, "harmful to animals."

The next important step in the development of knowledge about photosynthesis was the experiments of Sosuri, held in 1804. Weighing air and plants to photosynthesis and after, the sausure has established that the increase in the dry mass of the plant exceeded the mass of carbon dioxide absorbed from the air. Sosurur came to the conclusion that another substance participating in the increase in mass was water. Thus, 160 years ago, the process of photosynthesis was as follows:

H 2 O + CO 2 + HV -\u003e C 6 H 12 O 6 + O 2

Water + carbon dioxide + solar energy ----\u003e Organic substance + oxygen

Ingenhuz suggested that the role of light in photosynthesis lies in the splitting of carbon dioxide; In this case, oxygen is released, and the freaked "carbon" is used to build vegetable tissues. On this basis, living organisms were divided into green plants that can use solar energy for "assimilation" of carbon dioxide, and other organisms that do not contain chlorophyll, which cannot use light energy and are not capable of assimilating CO 2.

This principle of the division of the living world was violated when S. N. Vinogradsky opened the chemosynthetic bacteria in 1887 - adhelorophilic organisms capable of assimilating (i.e. turn into organic compounds) carbon dioxide in the dark. It was violated also when in 1883 Engelman opened purple bacteria, carrying out peculiar photosynthesis, not accompanied by oxygen release. At one time, this fact was not assessed in due measure; Meanwhile, the discovery of chemosynthetic bacteria assimilating carbon dioxide in the dark shows that the assimilation of carbon dioxide cannot be considered a specific feature of one photosynthesis.

After 1940, thanks to the use of labeled carbon, it was found that all cells are vegetable, bacterial and animals - capable of assimilating carbon dioxide, i.e., include it in organic substance molecules; Different only sources from which they draw the energy needed for this.

Another major contribution to the study of the photosynthesis process was introduced in 1905, Blackman, which found that photosynthesis consists of two consecutive reactions: a quick light reaction and a series of slower, non-light-dependent steps mentioned by them by the tempo reaction. Using high intensity light, Blackman showed that photosynthesis takes place at the same speed both during intermittent lighting with the duration of the flashes in just a fraction of a second and in continuous lighting, despite the fact that in the first case the photosynthetic system gets twice as much energy. The intensity of photosynthesis decreased only with a significant increase in the dark period. In further studies, it was found that the rate of the dark reaction increases significantly with increasing temperature.

The following hypothesis relative to the chemical base of photosynthesis was nominated by Van Nil, which in 1931 experimentally showed that the bacteria photosynthesis can occur in anaerobic conditions, not accompanied by the release of oxygen. Van Nile suggested that, in principle, the photosynthesis process was similar to bacteria and green plants. In the latter, light energy is used to photoles water (H 2 0) to form a reducing agent (H), determined by the carbon dioxide involved in the assimilation, and the oxidizing agent (it) is a hypothetical precursor of molecular oxygen. The bacteria photosynthesis flows in general the same, but hydrogen donor serves H 2 S or molecular hydrogen, and therefore oxygen is not occurring.

Modern ideas about photosynthesis

According to modern ideas, the essence of photosynthesis is to convert the radiant energy of sunlight into chemical energy in the form of ATP and reduced nicotinyndaenindinucleotide phosphate (NADF · H).

Currently it is assumed that the process of photosynthesis is consisted of two stages, in which the photosynthesising structures take actively participation [show] and photosensitive cell pigments.

Photosynthetic structures

In bacteria Photosynthetic structures are represented in the form of fusion of the cell membrane, forming plate organides of the mesosoma. Insulated mesosomes obtained by the destruction of bacteria are called chromatophores, a photosensitive device is concentrated in them.

Eukarotov The photosynthetic apparatus is located in special intracellular organoids - chloroplasts containing green chlorophyll pigment, which gives the plant green color and plays a crucial role in photosynthesis, catching the energy of sunlight. Chloroplasts, like mitochondria, also contain DNA, RNA and a device for protein synthesis, i.e., have a potential self-reproducing ability. In size, chloroplasts are several times more mitochondria. The number of chloroplasts varies from one in algae to 40 per cage at higher plants.

In the cells of green plants, in addition to chloroplasts, there are mitochondria, which are used for the formation of energy at night due to respiration, as in heterotrophic cells.

Chloroplasts have a spherical or compiled shape. They are surrounded by two membranes - outer and internal (Fig. 1). The inner membrane is stacked in the form of a stack of flattened bubble discs. This stack is called a gran.

Each grana consists of separate layers located like coin columns. The layers of protein molecules alternate with layers containing chlorophyll, carotes and other pigments, as well as special forms of lipids (containing galactose or sulfur, but only one fatty acid). These surfactant lipids appear to be adsorbed between the individual layers of molecules and serve to stabilize the structure consisting of alternating protein layers and pigments. Such a layered (lamellar) The structure of the garnet is likely to facilitate energy transfer in the process of photosynthesis from one molecule to the nearby.

In algae there is no more than one grain in each chloroplastic, and in higher plants - up to 50 graffiti, which are interconnected by membrane jumpers. The aqueous medium between the marins is the sturge of chloroplast, which contains enzymes carrying out "dark reactions"

Bubble structures, of which consists of grana, are called thylactoids. Granu from 10 to 20 thylactotoids.

The elementary structural and functional unit of photosynthesis of pylactotoid membranes, containing the necessary light-casting pigments and the components of the energy transformation apparatus, is called a quantosome consisting of about 230 chlorophyll molecules. This particle has a lot of about 2 x 10 6 daltons and the dimensions of about 17.5 nm.

	Stages of photosynthesis
	Light stage (or energy)	Dynamic stage (or metabolic)
Place the flow of reaction	In quantosomas, pylactotoid membranes, flows into the light.	It is carried out outside of thylactotoids, in the water medium, stroma.
Primary products	Energy of light, water (H 2 O), ADP, chlorophyll	CO 2, RIBULOZODIFOSFAT, ATP, NAPFN 2
Essence of the process	Photoliz of water, phosphorylation In the light stage of photosynthesis, the energy of light is transformed into the chemical energy of ATP, and the poor electrons of water turn into rich energies of the NADF electron · H 2. The side substance formed during the light stage is oxygen. The reaction of the light stage was called "light reactions".	Carboxylation, Hydrogenation, Defosphorylation In the dark stage of photosynthesis, "dark reactions" in which the reduction synthesis of glucose from CO 2 is observed. Without energy of the light stage, the dark stage is impossible.
End products	O 2, ATP, NAPFN 2 Rich Energy Products Light Reaction - ATP and Nadf · N 2 Next are used in the dark stage of photosynthesis.
The relationship between the light and dark stages can be expressed by the scheme. The process of photosynthesis Endergenic, i.e. It is accompanied by an increase in free energy, therefore requires a significant amount of energy supplied from the outside. Total photosynthesis equation: 6SO 2 + 12N 2 O ---\u003e C 6 H 12 O 62 + 6N 2 O + 6O 2 + 2861 kJ / mol.

Terrestrial plants absorb water the water through the roots needed for the process process, and the aqueous plants are obtained by diffusion from the environment. The carbon dioxide required for photosynthesis diffuses into the plant through the fine holes on the surface of the leaves - the dust. Since carbon dioxide is spent in the process of photosynthesis, its concentration in the cell is usually slightly lower than in the atmosphere. Oxygen released in the process of photosynthesis diffuses outward from the cell, and then from the plant - through the dust. Sugar formed during photosynthesis is also diffused in those parts of the plant, where their concentration is lower.

To implement photosynthesis, plants need a lot of air, as it contains only 0.03% of carbon dioxide. Consequently, 3 m 3 of carbon dioxide can be obtained from 10,000 m 3 of air, from which about 110 g of glucose is formed during photosynthesis. Typically, plants grow better at a higher content of carbon dioxide in the air. Therefore, in some greenhouses, the CO 2 content in the air is adjusted to 1-5%.

The mechanism of light (photochemical) stage of photosynthesis

In the implementation of photochemical functions of photosynthesis, solar energy and various pigments take part: green - chlorophylls A and B, yellow - carotenoids and red or blue - ficobilines. Photochemically active among this complex of pigments only chlorophyll a. The remaining pigments play an auxiliary role, being only collectors of light quanta (peculiar light-cutting lenses) and their conductors to the photochemical center.

Based on the ability of chlorophyll to effectively absorb the solar energy of a certain wavelength in tilactoid membranes, functional photochemical centers or photosystems were allocated (Fig. 3):

photosystem I (chlorophyll and) - Contains a pigment 700 (P 700) absorbing light with a wavelength of about 700 nm, plays a major role in the formation of photosynthesis light stage products: ATP and NADF · H 2
photosystem II (chlorophyll b.) - Contains the pigment 680 (P 680), absorbing light with a wavelength of 680 nm, plays auxiliary role. Flexing due to photolysis of water lost photosystem I electrons

On 300-400 molecules of light-cutting pigments in photosystems I and II accounts for only one photochemically active pigment molecule - chlorophyll a.

Plug-absorbed light quantum

translates the Pigment P 700 from the main state into the excited - p * 700, in which it easily loses the electron to form a positive electron hole in the form of p 700 + according to the scheme:
P 700 ---\u003e P * 700 ---\u003e P + 700 + E -
After that, the pigment molecule, which lost the electron, can serve as an electron acceptor (the electron is capable of accepting) and go to the restored form
causes decomposition (photocification) of water in the photochemical center R 680 photosystem II according to the scheme
H 2 O ---\u003e 2N + + 2E - + 1 / 2O 2
Photoliz of water is called Hill reaction. The electrons formed during the decomposition of water are initially accepted by the substance denoted by q (sometimes it is called cytochrome from 550 Po absorption maximum, although it is not cytochroma). Then from substance q through the carrier chain, similar to the composition on the mitochondrial, electrons are supplied in the photosystem I to fill the electron hole formed as a result of absorption by the system of light quanta, and the recovery of the pigment P + 700

If such a molecule simply gets back the same electron, it will be released by light energy in the form of heat and fluorescence (the fluorescence of pure chlorophyll is due to this). However, in most cases, the necessary negatively charged electron is accepted by special ironers (FES-center), and then

or transported on one of the chains of carriers back to P + 700, filling the electronic hole
or on another chain of carriers through ferredoxin and flavoproteide to constant acceptor - NADF · H 2

In the first case, there is a closed cyclic transport of an electron, and in the second - non-cyclic.

Both processes are catalyzed by the same electron carriers chain. However, with cyclic photo phosphaeling, electrons return from chlorophyll and again to chlorophyll and, whereas with non-cyclic photo phosphaeling electrons are moving from chlorophyll b to chlorophyll and.

Cyclic (photosynthetic) phosphorylation

Non-cyclic phosphorylation

As a result of cyclic phosphorylation, the formation of ATP molecules occurs. The process is associated with returning through a number of consecutive steps of excited electrons on p 700. The return of excited electrons on p 700 leads to the release of energy (in the transition from high to low energy level), which, with the participation of the phosphorylating enzyme system, is accumulated in phosphate bonds of ATP, and not dissipates in the form of fluorescence and heat (Fig.4.). This process is called photosynthetic phosphorylation (in contrast to oxidative phosphorylation carried out by mitochondria);

Photosynthetic phosphorylation - The primary reaction of photosynthesis is a mechanism for the formation of chemical energy (the synthesis of ATF from ADF and inorganic phosphate) on the chloroplastic thylactoid membrane using the energy of sunlight. Need for the dark reaction of assimilation CO 2

As a result of non-cyclic phosphorylation, there is a restoration of NADF + with the formation of NADF · N. The process is associated with the transfer of electron to ferredoxin, its restoration and further transition to its NADF +, followed by restoring it to Nadf · N.

In tilactoids are both processes, although the second is more complicated. It is conjugate (interrelated) with the work of the photosystem II.

Thus, the electrons lost p 700 are replenished due to electrons of water, decomposed under the action of light in the photosystem II.

and + to the ground state, they are formed, apparently, when excited chlorophyll b.. These high-energy electrons go to ferredoxine and then through flavoprotein and cytochrome - to chlorophyll and. At the last stage, phosphorylation of ADPs to ATP (Fig. 5) occurs.

Electrons necessary for the return of chlorophyll in Its main state is supplied, probably by ions of it - formed during water dissociation. Some of the water molecules dissociates N + ions and it is. As a result of the loss of electrons of ions, it is converted into radicals (OH), which further give the molecules of water and gaseous oxygen (Fig. 6).

This aspect of the theory is confirmed by the results of experiments with water and CO 2, labeled 18 0 [show] .

According to these results, the entire gaseous oxygen, released during photosynthesis, occurs from water, and not from 2. The reaction of the splitting of water has not yet been studied in detail. It is clear, however, that the implementation of all consecutive reactions of non-cyclic photophosphorylation (Fig. 5), including the excitation of one chlorophyll molecule and and one chlorophyll molecule b.must lead to the formation of one molecule of NADF · H, two or more ATP molecules from ADP and FN and to the release of one oxygen atom. For this, at least four quantum of light is necessary - two for each chlorophyll molecule.

Non-cyclic electron flow from H 2 O to NADF · H 2, which occurs in the interaction of two photosystems and binding their electron-vehicle circuits, is observed contrary to the values \u200b\u200bof the redox potentials: E ° for 1 / 2O 2 / H 2 O \u003d +0.81 V, and E ° for NADF / NADF · H \u003d -0.32 V. The energy of light turns the flow of electrons "reverse". It is essential that when transferring from the photose system II to the photosystem I, part of the electron energy is accumulated in the form of proton potential on the tilactoid membrane, and then into the energy of ATP.

The mechanism for the formation of proton potential in the electron transfer circuit and its use on the formation of ATP in chloroplasts is similar to those in mitochondria. However, there are some features in the photophosphorylation mechanism. Tilactoids are as part of the inside out of mitochondria, therefore the direction of transferring electrons and protons through the membrane is the opposite to the direction of it in the mitochondrial membrane (Fig. 6). Electrons move to the outside, and protons are concentrated inside the thilactoid matrix. The matrix is \u200b\u200bcharged positively, and the outer membrane of tilacto - is negative, that is, the direction of the proton gradient is opposite to the direction of it in mitochondria.

Another feature is a significantly large share of pH in proton potential compared to mitochondria. The thilactoid matrix is \u200b\u200bstrongly overlapping, therefore Δ pH can reach 0.1-0.2 V, while Δ ψ is about 0.1 V. The total value of Δ μ H +\u003e 0.25 V.

H + -atf synthetase, denoted in chloroplasts as complex "CF 1 + F 0", is also oriented in the opposite direction. Her head (F 1) looks outward, towards the stroma of chloroplast. Protons are pushed out through CF 0 + F 1 from the matrix outward, and in the active center F 1 is formed atf due to the energy of proton potential.

In contrast to the mitochondrial chain in Tilactotoid, there is apparently only two sections of the conjugation, therefore, on the synthesis of one ATP molecule, instead of two three protons, i.e., the ratio of 3 H + / 1 mol ATP is required.

So, in the first stage of photosynthesis, during light reactions, ATP and NADF are formed in the stroma of chloroplast. · H - products necessary for the implementation of dark reactions.

The mechanism of the dark stage of photosynthesis

The dark reactions of photosynthesis are the process of incorporating carbon dioxide into organic matter with the formation of carbohydrates (glucose photosynthesis from CO 2). Reactions flow in the stroma of chloroplast with the participation of products of the light stage of photosynthesis - ATP and NADF · H2.

Assimiation of carbon dioxide (photochemical carboxylation) is a cyclic process, which is also called a pentosophosphate photosynthetic cycle or Calvin cycle (Fig. 7). It includes three main phases:

carboxylation (fixation with 2 ribulosecodiphosphate)
recovery (the formation of trioseophosphates during the restoration of 3-phosphoglycerat)
regeneration of Ribulosodiphosphate

Ribulose-5-phosphate (sugar containing 5 carbon atoms, with phosphate residue in carbon at position 5) is subject to phosphorylation due to ATP, which leads to the formation of ribulose phyphosphate. This last substance is carboxylated by attaching CO 2, apparently to an intermediate six-carbon product, which, however, is immediately split off with the addition of water molecule, forming two phosphoglycerolic acid molecules. The phosphoglycerin acid is then restored during an enzymatic reaction, for the implementation of which the presence of ATP and NADF is required. · H with the formation of phosphoglycerin aldehyde (three-carbon sugar - triosis). As a result of the condensation of two such triosis, the hexose molecule is formed, which can be included in the starch molecule and thus postponed about the supply.

To complete this phase of the cycle during photosynthesis, 1 C0 2 molecule is absorbed and 3 ATP molecules and 4 N atom (connected to 2 molecules above · N). From hexosophosphate by certain pentosophosphate cycle reactions (Fig. 8) regenerates ribulosestic phosphate, which can again attach another carbon dioxide molecule.

None of the described reactions - carboxylation, recovery or regeneration - cannot be considered specific only for the photosynthetic cell. The only difference detected in them is that for the recovery reaction, during which phosphoglycerin acid turns into phosphoglycerin aldehyde, NADF is needed. · N, not over · H, as usual.

Fixation with 2 ribulosecodiphosphate is catalyzed by the enzyme ribulosephosphorboxylase: ribulosephosphate + CO 2 -\u003e 3-phosphoglycerat Next 3-phosphoglycerat is restored with NADF · H 2 and ATP to glyceraldehyde-3-phosphate. This reaction is catalyzed by the enzyme - glyceraldehyde-3-phosphate dehydrogenase. Glyceraldehyde-3-phosphate is easily amazed in dihydroxyacetone phosphate. Both trioseophosphate are used in the formation of fructosophosphate (reverse reaction, catalyzed by fructose-bisphosfat-aldolase). Part of the molecules of the fructosophosphate formed together with trioseophosphates in the regeneration of ribulosecodiphosphate (closed the cycle), and the other part is used to stock carbohydrates in photosynthetic cells, as shown in the diagram.

It is estimated that for the synthesis of one molecule of glucose from CO 2 in the Calvin cycle, 12 NADF is required · H + H + and 18 ATP (12 ATP molecules are spent on the reduction of 3-phosphoglycerat, and 6 molecules - in reactions of regeneration of ribulosephosphate). Minimum ratio - 3 ATP: 2 NADF · H 2.

It is possible to notice the generality of the principles underlying photosynthetic and oxidative phosphorylation, with photophosphorylation, as it were, as if facing oxidative phosphorylation:

The energy of light is the driving force of phosphorylation and the synthesis of organic substances (S-H 2) during photosynthesis and, on the contrary, the energy of oxidation of organic substances - with oxidative phosphorylation. Therefore, it is plants that provide life to animals and other heterotrophic organisms:

Carbohydrates formed during photosynthesis are served to construct carbon skeletons of numerous organic substances of plants. Azorganic substances are absorbed by photosynthetic organisms by restoring inorganic nitrates or atmospheric nitrogen, and sulfur - restoration of sulfates to sulfhydryl groups of amino acids. Photosynthesis ultimately provides the construction of not only mandatory proteins, nucleic acids, carbohydrates, lipids, cofactors, but also numerous secondary synthesis products, which are valuable drugs (alkaloids, flavonoids, polyphenols, terpenes, steroids, organic acids, etc. .).

Bloodless photosynthesis

Bloodless photosynthesis is found in salular-baked bacteria having a purple light-sensitive pigment. This pigment was protein bacterioropopsin, containing, like a visual purple of the retina - Rhodopsin, a derivative of vitamin A - Retinal. Bariodopsin, built into the membrane of salular-bique bacteria, forms in this membrane in response to the absorption of the light of light the proton potential transformed into ATP. Thus, bacterioriodopsin is an inhlormal converter of light energy.

Photosynthesis and external environment

Photosynthesis is possible only in the presence of light, water and carbon dioxide. PDA photosynthesis is not more than 20% in cultural species of plants, and usually it does not exceed 6-7%. In an atmosphere of about 0.03% (about.) CO 2, with an increase in its content up to 0.1%, the intensity of photosynthesis and the productivity of plants increase, therefore it is advisable to feed the plants by hydrocarbonates. However, the content of CO 2 in the air above 1.0% has a harmful effect on photosynthesis. For the year, only terrestrial plants assimilate 3% of total from 2 atmosphere of the Earth, that is, about 20 billion tons. In the composition of the coated from 2 carbohydrates, it is accumulated to 4 · 10 18 kJ of light energy. This corresponds to the power of the power plant in 40 billion kW. Photosynthesis by-product - oxygen - vital for higher organisms and aerobic microorganisms. Save vegetation cover - it means to save life on Earth.

Fotosynthesis efficiency

The efficiency of photosynthesis in terms of biomass production can be estimated through the share of total solar radiation falling on a specific area for a certain time, which is inhibited in the organic matter of the crop. The productivity of the system can be estimated by the number of organic dry matter obtained from a unit of the area for the year, and express in units of mass (kg) or energy (MJ) products obtained from hectare per year.

The yield of biomass depends, thus, from the system of solar energy (leaves) operating during the year, and the number of days a year with such conditions of illumination, when photosynthesis is possible at maximum speed, which determines the effectiveness of the entire process. The results of determining the proportion of solar radiation (in%) affordable plants (photosynthetically active radiation, headlights), and knowledge of the main photochemical and biochemical processes and their thermodynamic, efficiency allow you to calculate the likely limit velocities for the formation of organic substances in terms of carbohydrates.

Plants use light with a wavelength from 400 to 700 nm, that is, the share of photosynthetically active radiation accounts for 50% of the total sunlight. This corresponds to the intensity on the surface of the Earth 800-1000 W / m 2 for a regular sunny day (on average). The average maximum efficiency of energy transformation during photosynthesis in practice is 5-6%. These estimates were obtained based on the study of the process of binding CO 2, as well as related physiological and physical losses. One praying CO 2 in the form of a carbohydrate corresponds to the energy of 0.47 MJ, and the energy of red light quanta with a wavelength of 680 nm (the poorest energy used in photosynthesis) is 0.176 MJ. Thus, the minimum number of moles of the red light quanta needed for binding 1 praying CO 2 is 0.47: 0.176 \u003d 2.7. However, since the transfer of four electrons from water to fix one CO 2 molecule requires at least eight light quanta, the theoretical binding efficiency is 2.7: 8 \u003d 33%. These calculations are made for red light; It is clear that for white light, this value will be appropriately below.

In the best field conditions, the fixation efficiency in plants reaches 3%, but this is possible only in short periods of growth and, if you recalculate it for the whole year, it will be somewhere between 1 and 3%.

In practice, on average, the effectiveness of photosynthetic energy transformation in zones with temperate climates is usually 0.5-1.3%, and for subtropical crops - 0.5-2.5%. The product output that can be expected at a certain level of the intensity of sunlight and the different efficiency of photosynthesis, it is easy to estimate from the graphs shown in Fig. 9.

Meaning of photosynthesis

The photosynthesis process is the basis for the nutrition of all living beings, and also supplies humanity with fuel, fibers and countless useful chemical compounds.
Of the carbon dioxide and water connected from the air during photosynthesis, about 90-95% of the dry weight of the harvest is formed.
A person uses about 7% of photosynthesis products in food, as animal feed, in the form of fuel and building materials

General equation photosynthesis: 6CO 2 + 6 H 2 O --- (light, chloroplasts) ---\u003e C 6 H 12 O 6 + 6 O 2. During this process, a carbohydrate glucose is formed from substances, poor energy - carbohydrates (C 6 H 12 O 6) - the substance is rich in energy, and molecular oxygen is also formed. Very figuratively described this phenomenon Russian scientist, physiologist of plants - K.A. Timiryazev.

The photosynthesis equation corresponds two partial reactions:

1) Light reaction or conversion of energy-process of localization in chloroplast thylaquets. ]

2) a dark reaction or conversion of substances-process of localization in a stroma of chloroplast.

3.List as a body photosynthesis.A plate of photosynthesis, which absorbs and spares solar energy and carries out gas exchange with the atmosphere. On average, the sheet absorbs 80-85% of photosynthetically active radiation (headlights) and 25% of the energy of infrared rays. 1.5-2% of the absorbed headlights are spent on photosynthesis, the remaining energy is spent on evaporation of water-transpiration. The sheet is distinguished by a flat structure and a small thickness. The architectonics of plants - the spatial location of the organs, the leaves are located on the plant without flaming each other. Features ensuring the efficiency of photosynthesis: 1) the presence of coating tissue-epidermis, protecting the sheet from excessive water loss. The cells of the lower and upper epidermis are devoid of chloroplasts and have large vacuoles. As lenses focus the light on the detached chlorofilic fabric. The lower and the upper epidermis have dust, through which the diffusion of CO2 occurs inside the sheet.2) the presence of specialized photosynthetic tissue-chlorine. The main chlorophilic fabric is a parisadic parenchyma, which is located on the lighted part of the sheet. In each cell of the panelous parenchyma, there are 30-40 chloroplasts. 3) The presence of a highly developed system of veins conductive paths, which ensures the rapid outflow of assimilates and the supply of photosynthetic cells with water and the necessary mineral substances. Depending on the external conditions for the Cat, the formation and functioning of the leaves anatomical structure may vary.

4.Structure and functions of chloroplasts.Chloroplasts - plastids of higher plants, in which the process of photosynthesis is underway, that is, the use of energy of light rays to form organic substances from inorganic substances (carbon dioxide and water) with simultaneous oxygen to the atmosphere. Chloroplasts have the shape of a double lens, their size is about 4-6 microns. They are in parenchymal cells of leaves and other green parts of higher plants. Their number in the cell varies within 25-50.

Outside, chloroplast is covered with a shell consisting of two lipoprotein membranes, external and internal. Both membranes have a thickness of about 7HM, they are separated from each other in front of 20-30 nm. The inner membrane of chloroplasts, as well as other plastids forms folded piercing inside the matrix or stroma. Two types of internal membranes are visible in the mature chloroplastic of higher plants. These membranes forming flat, extended stroma lamellas, and pylakoid membranes, flat disc-vacuine vacuoles or bags.

The main function of chloroplasts, consists in catching and transformation of light energy.

The composition of the membranes forming the grains includes green pigment - chlorophyll. It is here that the light reactions of photosynthesis occur - absorb chlorophyll light rays and the conversion of light energy into the energy of excited electrons. Electrons excited by light, i.e., with excess energy, give their energy to decomposition of water and the synthesis of ATP. When water decomposition, oxygen and hydrogen are formed. Oxygen is released into the atmosphere, and hydrogen is associated with protein ferredoxin.

Chloroplasts have known autonomy in the cell system. They have their own ribosomes and a set of substances that determine the synthesis of a number of its own proteins of chloroplast. There are also enzymes whose work leads to the formation of lipids included in the lamella and chlorophyll. Thanks to all this, chloroplasts can independently build their own structures. Another very important function is to absorb carbon dioxide in chloroplast or, as it is customary, fixing carbon dioxide, that is, the inclusion of its carbon into organic compounds

5.Pigments of the photosynthetic apparatus (total. Characteristics)The ability of plants to carry out photosynthesis is related to the presence of pigments. The main one is the magnesium-containing porphyrin pigment - chlorophyll.

In nature, there are five different types of chlorophyll, which differ slightly in their molecular structure. Chlorophyll A is present in all algae and higher plants; Chlorophyll B - in green, chas and eurgy and higher plants; chlorophyll C - in brown algae, golden, diatoms and dinoflagellate; chlorophyll d - in red algae; Chlorophyll e only once, apparently, it is chlorophyll; Finally, various types of bacteriochlorophyll - in photosynthetic bacteria. For cinema and red algae, biliproteins are characterized by the presence of biliproteins: phycocyanin and ficoeroidrin. The most well studied chlorophyll a. Its molecule consists of four pyrroned rings, with nitrogen which is associated with a magnesium atom, and one of the rings is attached a single butter-unsaturated alcohol phytol.

The chlorophyll molecule is built into the membrane - immersed by a hydrophobic phytol chain into its lipid part. Clean solution of chlorophyll A has a maximum absorption at 663 nm. In an intact, intact, normally functioning cell, chlorophyll is characterized by maxima absorption at 672 and 683 nm. The high efficiency of the absorption of light by chlorophylls is due to the presence in their molecule of a large number of conjugate double ties.