General and partial photosynthesis equations. Total photosynthesis equation Total photosynthesis reaction equation

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 substancesand 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 · N).

Currently it is considered that the process of photosynthesis is consisted of two stages in which active participation Take photosynthesizing structures [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 but) - 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

1. or transported on one of the chains of carriers back to P + 700, filling the electronic hole
2. 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 but again to chlorophyll but, whereas with non-cyclic photo phosphaeling electrons are moving from chlorophyll b to chlorophyll but.

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 (when moving from high to low energy level), which, with the participation of the phosphorylating enzyme system, is accumulated in the 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.

but + 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 but. 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 but 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. nine.

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

The chemical equation of the photosynthesis process in general can be represented as follows:

6So 2 + 6N 2 O + QSW → C 6 H 12 O 6 + 6O 2.

Photosynthesis is a process at which the electromagnetic energy of the Sun chlorophyll and auxiliary pigments is absorbed and the conversion of it into chemical energy, absorb carbon dioxide from the atmosphere, restoring it into organic compounds and the return of oxygen into the atmosphere.

In the process of photosynthesis from ordinary not organic compounds (CO 2, H 2 O) various organic compounds are built. As a result, chemical bonds are restructuring: instead of C - O and H - O relations, C - C and C - H bonds arise, in which electrons occupy a higher energy level. Thus, rich in energy organic substances that feed and at the expense of which the energy is obtained (in the process of breathing) animals and people are originally created in a green leaf. It can be said that almost all live matter on Earth is the result of photosynthetic activities.

The date of opening of the photo sectine process can be considered 1771. English scientist J. Priestley drew attention to the change in the composition of the air due to animal vital activity. In the presence of green plants, the air again became suitable for both breathing and burning. In the future works of a number of scientists (Ya. Ingengauses, J. Sebeje, T. Sosurhur, J.B. Bushengo) It was found that green plants from the air absorb C0 2, from which organic substance is formed when the water participation in the light is formed. It is this process in 1877. The German scientist V. Pfeffer called photosynthesis. Great importance To disclose the essence of photosynthesis, there was a law of conservation of energy formulated by R. Mayer. In 1845, R. Mayer put forward the assumption that the energy used by plants is the energy of the Sun, which plants in the process of photosynthesis are converted into chemical energy. This provision was developed and experimentally confirmed in the studies of the wonderful Russian scientist K.A. Timiryazeva.

Photosynthesis includes both light and dark reactions. A number of experiments have been conducted proving that in the process of photosynthesis, not only reactions running using light energy, but also dark, which do not require the direct participation of light energy. The following evidence of the existence of dark reactions in the process of photosynthesis can be brought:

1) Photosynthesis is accelerated with increasing temperature. Hence it directly follows that some stages of this process are not directly related to the use of light energy. Especially sharply, the dependence of photosynthesis on temperature is manifested at high light intensities. Apparently, in this case, the speed of photosynthesis is limited by precisely dark reactions;

2) The efficiency of using the energy of light in the process of photosynthesis was higher with intermittent lighting. At the same time for more effective use Light energy The duration of dark gaps should significantly exceed the duration of light.

Pigments photosynthesis

In order for the light to have an impact on the plant organism and, in particular, to be used in the process of photosynthesis, its absorption of pigment photoreceptors is necessary. Pigments - These are painted substances. Pigments absorb the light of a certain wavelength. Uncurred sections of the solar spectrum are reflected in what causes the painting of pigments. So, the green pigment chlorophyll absorbs the red and blue rays, while the green rays are mainly reflected. The visible part of the solar spectrum includes wavelengths from 400 to 700 nm. Substances absorbing the entire visible section of the spectrum seem black.

Pigments concentrated in plasts can be divided into three groups: chlorophylls, carotenoids, ficobilins.

To group chlorophylls Organic compounds that contain 4 pyrrole rings connected by magnesium atoms and having a green color.

Currently known about ten chlorophylls. They differ in the chemical structure, painting, distribution among living organisms. All higher plants contain chlorophylls a and b. Chlorophyll with detected in diatoms of algae, chlorophyll D - in red algae.

The main pigments, without which photosynthesis does not go, are chlorophyll and for green plants and bacterochlorophylls for bacteria. For the first time, the exact idea of \u200b\u200bthe pigments of the green sheet of higher plants was obtained thanks to the works of the largest Russian botany M.S. Colors (1872-1919). He developed a new chromatographic method of separation of substances and allocated sheet pigments in its pure form.

The chromatographic method of separation of substances is based on their different adsorption ability. This method was widely used. M.S. The color passed the hood from a sheet through a glass tube filled with powder - chalk or sucrose (chromatographic column). Separate components of the mixture of pigments differed according to the degree of adsorbability and moved at different speeds, as a result of which they were concentrated in different column zones. Separating a column for individual parts (zones) and using the appropriate system of solvents, each pigment could be allocated. It turned out that the leaves of higher plants contain chlorophyll a and chlorophyll b, as well as carotenoids (carotene, xanthofill, etc.). Chlorophylls, as well as carotenoids, insoluble in water, but are well soluble in organic solvents. Chlorophylls A and B differ in color: chlorophyll A has a blue-green shade, and chlorophyll B is yellow-green. The chlorophyll content in the sheet is about three times more compared to chlorophyll b.

Carotenoids - These are yellow and orange pigments of aliphatic structure, derived isoprene. Carotenoids are contained in all higher plants and many microorganisms. These are the most common pigments with a variety of features. Carothindes containing oxygen received the name Xantofilla. The main representatives of the carotenoids in higher plants are two pigments - carotene (orange) and xanthofill (yellow). Unlike chlorophylls, carotenoids do not absorb red rays, and also do not have the ability to fluorescence. Like chlorophyll, carotenoids in chloroplasts and chromatophoras are in the form of proteins insoluble in water. Carotenoids, absorbing certain sections of the solar spectrum, transmit the energy of these rays on the chlorophyll molecules. Thus, they contribute to the use of rays that chlorophyll are not absorbed.

Fikobilins - Red and blue pigments contained in cyanobacteria and some algae. Studies have shown that red algae and cyanobacteria along with chlorophyll and contain ficobilins. The basis of the chemical structure of Fikobilins is four pyrrolers.

Fikobilins are represented by pigments: a phycocyanin, ficoeryroid and alloficogenin. Ficoeroidrin is an oxidized ficotian. Ficobilines form durable compounds with proteins (ficobilinproteides). The relationship between ficobilies and proteins is destroyed only by acid.

Fikobilins absorb rays in green and yellow parts of the solar spectrum. This is the part of the spectrum that is between the two main absorption lines of chlorophyll. Ficoeroidrin absorbs rays with a wavelength of 495-565 nm, and a phycocianine is 550-615 nm. A comparison of the spectra of the absorption of ficobilines with spectral composition of light, in which photosynthesis in cyanobacteria and red algae shows that they are very close. This suggests that the ficobilines absorb the energy of light and, like carotenoids, transmit it to the chlorophyll molecule, after which it is used in the process of photosynthesis. The presence of ficobilins in algae is an example of the adaptation of organisms in the process of evolution to the use of sections of the solar spectrum, which penetrate through the thickness sea water (chromatic adaptation). As is known, the red rays corresponding to the main absorption line of chlorophyll, are absorbed by passing through the thickness of the water. Green rays are most deeply penetrated, which are not absorbed by chlorophyll, but ficobilians.

Properties of chlorophyll

All chlorophylls are magnesium salts of Pyrrole. In the center of the chlorophyll molecule there are magnesium and four pyrrole rings, connected with each other with methane bridges.

By the chemical structure of chlorophylls - the esters of dicarboxylic acid - chlorophylline and two residues of alcohols - phytola and methyl.

The most important part of the chlorophyll molecule is the central kernel. It consists of four pyrroleous five-membered rings, interconnected by carbon bridges and forming a large porphyrin core with nitrogen atoms in the middle associated with the magnesium atom. In the chlorophyll molecule, there is an additional cyclopentaneon ring that contains carbonyl, as well as carboxyl groups associated with ethereal tie with methyl alcohol. The presence in the porphyrin core conjugated in a circle of the system of ten double ties And magnesium causes green color characteristic for chlorophyll.

Chlorophyll is different from chlorophyll as well as instead of a metal group in the second pyrrol ring has an aldehyde group sleep. Chlorophyll has a blue-green color, and chlorophyll B is light green. They are adsorbed in different layers of chromatograms, which indicates different chemicals and physical properties. According to modern ideas, the biosynthesis of chlorophyll in goes through chlorophyll a.

Fluorescence is the property of many bodies under the influence of falling light, in turn, emit light: while the wavelength of the emitted light is usually larger than the wave of the excitation light. One of the most important properties of chlorophylls is their pronounced ability to fluorescence, which is intense in solution and depressed in chlorophyll, contained in the tissues of the leaves, in plastids. If you look at the solution of chlorophyll in the rays of light passing through it, then it seems emerald green, if we consider it in the rays of reflected light, then it acquires red color - this is the fluorescence phenomenon.

Chlorophylls differ in the absorption spectra, with chlorophyll B compared with chlorophyll and the absorption band in the red region of the spectrum is somewhat shifted towards short-wave rays, and in the blue-purple region, the absorption maximum is shifted towards long-wave (red) rays.

Photosynthesis - biological processtranslating electrons by electron transport circuit from one redox system to another.

With photosenthesis of plants from carbon dioxide and water, carbohydrates are formed:

(Total photosynthesis reaction).

The role of the donor of electrons or hydrogen atoms for the subsequent restoration of the SHA in the process of photosynthesis in plants plays water. Therefore, the equation describing photosynthesis can be rewritten as

With a comparative study of photosynthesis, it was found that in photosynthetic cells as an electron acceptor

(or hydrogen atoms), except C0 2, in some cases nitrate-ion protrude, molecular nitrogen or even hydrogen ions. In the role of electron donors or hydrogen atoms, in addition to water, hydrogen sulfide, isopropyl alcohol and any other possible donor, depending on the type of photosynthetic cells, can perform.

To implement the total reaction of photosynthesis, it is necessary to spend the energy of 2872 kJ / mol. In other words, it is necessary to have a restoring agent with a sufficiently low redox potential. With the photosynthesis of plants, the reducing agent serves as NADPH +.

Photosynthesis reactions proceed to chloroplast * Cells of green plants - intracellular organelles similar to mitochondria and also having their own DNA. Internal membrane structures in chloroplasts - tylacoids - Contain chlorophyll (Pigment, capturing light), as well as all electron carriers. Free from thylacoids space inside chloroplast call stroma

In the light-dependent part of the photosynthesis, the "light reaction", there is a splitting of molecules H 2 0 to the formation of protons, electrons and an oxygen atom. Electrons, "excited" energy of light reaches the level of energy sufficient to restore NADP +. The resulting NADP + H +, in contrast to H 2 0, is a suitable reducing agent for the transfer of carbon dioxide into an organic compound. If NADPH + H +, ATP and the corresponding enzymes are present in the system, C0 2 fixation may also flow in the dark; Such a process is called temova reaction.

Thylacoid membrane contains three types of complexes (Fig. 16.2). The first two are associated with diffusory carriers of electrons - plastokhinone (Q), similar in structure for ubiquinone, and the third - small water-soluble protein - plastocianin (PC), also involved in the transfer of electrons. It contains copper atom, which serves that donor, then an electron acceptor (alternately is in a state of C + or C 2+). These three types of complexes are referred to photosystem II (FS II), complex cytochrome / (cyt B / F) consisting of two cytochromes and a ironing center and carrying out electrons from the reduced plastochinone to the plastocianin, and photosystem I. (FS. I). The numbering of photosystems reflects the order of their discovery, and not the procedure for entering the transfer circuit.

Fig. 16.2.

The function of all this apparatus is to implement the total reaction.

The reaction is accompanied by a large increase in Gibbs energy entering the system in the form of sunlight: the formation of two absorbed quanta is spent on the formation of each NADPH molecule.

The photon energy is directly proportional to the frequency of the incident light and can be calculated using the Einstein formula that determines energy E. One "Praying" of light quanta, equal to 6.023-10 23 quanta (1 Einstein):

Here N. - the number of Avogadro (6,023-10 23 1 / mol); h. - Permanent Planck (6,626-10 34 J / s); v - frequency of falling light, numerically equal to attitude s / x, where C is the speed of light in vacuum (3.0-10 8 m / s); X. - wavelength of light, m; E. - Energy, J.

When the photon is absorbed, an atom or molecule is moving into an excited state with greater energy. Only photons with a certain wavelength can be excited or a molecule, since the excitation process is discrete (quantum) character. The excited state is extremely unstable, the return to the main state is accompanied by energy loss.

In plants, the receptor absorbing light serves the chlorophyll molecule but, The chemical structure of which is shown below.

Chlorophyll - It is a tetrapyrrol, resembling a gem structure. In contrast to the heme, the central chlorophyll atom is magnesium, and one of the side chains contains a long hydrophobic hydrocarbon chain, "anchor" holding chlorophyll in the lipid bisal membrane of tylacoid. Like a gem, chlorophyll has a system of conjugate double bonds that determine the appearance of intensive color. In green plants, chlorophyll molecules are packed in photosystems consisting of chlorophyll molecules, catching light, reaction center and electron transfer circuit.

Chlorophyll in the composition of the FS II is denoted by p 680, and in the FS I - P 7 oo (from the English, pigment - pigment; The number corresponds to the wavelength of the maximum absorption of light in Nm). Chlorophyll molecules, downloading energy to such centers, called antenna. The combination of absorption of chlorophyll molecules of these two wavelengths gives a higher photosynthence rate than when the light is absorbed by each of these wavelengths separately. Photosynthesis in chloroplasts is described by the so-called Z schema (from FR. zigzag).

Chlorophyll P 6 8o in the reaction centers of the FS II in the dark is mainly state, without showing any rehabilitation properties. When R 680 receives the photon energy from the antenna chlorophyll, it goes into an excited state and seeks to give the electron, which turned out to be at the top energy level. As a result, this electron acquires a carrier of electrons of the FS II - Feofitin (pH) - pigment, in its structure similar to chlorophyll, but not containing Mg 2+.

Two restored faeofitin molecules consistently give the obtained electrons to restore the plasticon-soluble in the lipids of the carrier of electrons from the FS II to the b / f cytochrome complex.

In the reactionary center of FS I, the chlorophyll R700 also flows the photon energy caught by antenna chlorophyll. At the same time, the P700 becomes a powerful reducing agent. Electrical chlorophyll p 7 oo is transmitted over a short chain on ferredoxin (FD) is a water-soluble stroma protein containing an electron-coceptor cluster of iron atoms. Ferredoxine with FAD-dependent enzyme ferredok- Sin-Nadp * -Repotasis Restores NADP + to NADPH.

To return to the original (main) state of P 7 OO acquires an electron at the restored plastocianin:

In the FS II of RB80 + returns to its original state, obtaining an electron from water, since its gentlement is higher than at oxygen.

Photosynthesis differs from other biochemical processes by the fact that the restoration of NADP + and the Synthesis of ATRs occur due to the energy of light. All further chemical transformations, during which glucose and other carbohydrates are formed, are not fundamentally different from enzymatic reactions.

Key metabolite is 3-phosphoglycerat, Of which the carbohydrates are further synthesized in the same way as in the liver, with the only difference that the reducing agent in these processes is NADPH, and not NADH.

The synthesis of 3-phosphoglycerat from carbon dioxide is carried out using an enzyme - ribulosodiphosphate carboxylase / oxygenase:

Carboxylase splits the ribulose-1,5-diphosphate into two 3-phosphoglycerat molecules and at the same time connects one carbon dioxide molecule.

Attachment (fixation) of carbon dioxide occurs in a cyclic process, referred to calvin cycle.

Total cycle reaction:

When catabolism, this reaction goes in the opposite direction (see ch. 12).

The consistency of the Calvin cycle reactions can be represented as follows:

At the 15th stage, the cycle ends and 6 ribulose-1,5-diphosphate enters the 1st stage.

So, with photosynthesis in plants, carbon dioxide is included in the carbon skeleton of glucose as a result of a dark reaction with riblose-1.5-phosphate with the formation of 3-phosphoglycerat (1st stage of the cycle).

IN vegetable world Carbohydrates accumulate in large quantities as a spare nutritious material (starch). Polisaccharide starch is formed as a result of glucose polymerization obtained in the 8th stage.

1. Give definitions of concepts.
Photosynthesis - The process of formation of organic substances from carbon dioxide and water in light with the participation of photosynthetic pigments.
Avtotropy. - Organisms synthesizing organic substances from inorganic.
Heterotrophs - organisms that are not able to synthesize organic substances from inorganic means of photosynthesis or chemosynthesis.
Mixotrophs. - Organisms that can use various carbon and energy sources.

2. Fill in the table.

3. Fill in the table.

4. Explain the essence of the approval of the Great Russian scientist K. A. Timiryazeva: "Polyenoe is canned solar energy."
Pulling is part of the tree, the fabric is consisting of accumulated organic compounds (cellulose, sugar, etc.), which were formed during photosynthesis.

5. Write the total photosynthesis equation. Do not forget to indicate the mandatory conditions for reactions.

12. Select Term and explain how much it is modern value corresponds to the initial value of its roots.
Selected term - mixotrophs.
Conformity. The term is clarified, so called organisms with mixed nutritional type, which can use various carbon and energy sources.

13. Word and write down the main ideas § 3.3.
By type of nutrition, all living organisms are divided into:
AutoTrophic, synthesizing organic substances from inorganic.
Heterotrophs feed on ready-made organic substances.
Mixed mixed nutrition.
Photosynthesis is the process of formation of organic substances from carbon dioxide and water in light with the participation of photosynthetic pigments by phototrobes.
It is divided into the light phase (the water molecules and H + are formed, necessary for the dark phase, as well as oxygen) and the dark (glucose is formed). Total photosynthesis equation: 6SO2 + 6N2O → C6H12O6 + 6O2. It proceeds into the light in the presence of chlorophyll. So the energy of light turns into
the energy of chemical bonds, and plants form glucose and sugar for themselves.

Photosynthesis is the transformation of light energy into the energy of chemical ties organic compounds.

Photosynthesis is characteristic of plants, including all algae, a number of prokaryotes, including cyanobacteria, some unicellular eukaryotes.

In most cases, at photosynthesis, oxygen (O 2) is formed as a by-product. However, this is not always the case because there are several different paths of photosynthesis. In the case of oxygen is released, it is water from which hydrogen atoms are cleaved for the needs of photosynthesis.

Photosynthesis consists of a variety of reactions in which various pigments, enzymes, coenzymes, etc. are involved. The main pigments are chlorophylls, except for them - carotenoids and ficobilines.

In nature, two ways of photosynthesis of plants are common: C 3 and C 4. Other organisms have their own specifics of reactions. All that unites these different processes Under the term "photosynthesis," - in all of them, a total of photons in a chemical bond. For comparison: during chemosynthesis, energy is converted chemical bond One compounds (inorganic) to others - organic.

Two phases of photosynthesis are isolated - light and dark. The first depends on the light radiation (hν), which is necessary for the flow of reactions. The dark phase is light-dependent.

In plants, photosynthesis flows in chloroplasts. As a result of all reactions, primary organic substances are formed, of which carbohydrates, amino acids, fatty acids, etc. are also synthesized, and others. Usually the total reaction of photosynthesis is written in relation to glucose - the most common photosynthesis product:

6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2

Oxygen atoms included in the O 2 molecule are not taken from carbon dioxide, but from water. Carbon dioxide - carbon sourceMore importantly. Thanks to its binding, plants appear the possibility of organic synthesis.

Presented above chemical reaction There is generalized and total. It is far from the essence of the process. So glucose is not formed from six separate carbon dioxide molecules. CO 2 binding occurs in one molecule, which first joins the already existing five-carbon sugar.

For prokaryotes are characterized by photosynthesis. So in bacteria, the main pigment is bacteriohlorophyll, and oxygen is not released, since hydrogen is not taken out of water, but often from hydrogen sulfide or other substances. In blue-green algae, the main pigment is chlorophyll, and oxygen is released at photosynthesis.

Light phase photosynthesis

In the light phase of photosynthesis, the synthesis of ATP and NADF · H 2 occurs due to radiant energy. It happens on thylacoids of chloroplastswhere pigments and enzymes form complex complexes for the functioning of electrochemical chains, according to which electrons and partly the protons of hydrogen are transmitted.

The electrons ultimately turn out to be the Nadf Coenzyme, which, charging negatively, attracts part of the protons and turns into NADF · H 2. Also, the accumulation of protons on one side of the thylacoid membrane and electrons by another creates an electrochemical gradient, the potential of which is used by the ATP-synthetase enzyme for the ATP and phosphoric acid synthesis.

The main pigments of photosynthesis are various chlorophylls. Their molecules capture radiation of certain, partly different spectra of light. At the same time, some electrons of chlorophyll molecules are moving to a higher energy level. This is an unstable state, and in the idea of \u200b\u200belectrons by the same radiation should be in space obtained from out of energy and return to the previous level. However, in photosynthetic cells, excited electrons are captured by acceptors and with a gradual decrease in its energy are transmitted along the carrier chains.

Tylacoid membranes exist two types of photosystems emitting electrons with light action. Photosystems are a complex complex mostly in chlorophilic pigments with a reaction center, from which electrons are broken. In the photo system, sunlight catches many molecules, but all the energy is collected in the reaction center.

Photosystem I electrees, passing along the chain of carriers, restore the NADF.

Energy of electrons that ripped from the Photosystem II is used to synthesize ATP. And the electrons of the photosystem II themselves fill electronic holes of the photosystem I.

The holes of the second photosystem are filled with electrons resulting from photolis of water. Photoliz also occurs when the light participation and lies in the decomposition of H 2 O to protons, electrons and oxygen. It is as a result of photoles of water formed free oxygen. Protons are involved in the creation of an electrochemical gradient and the restoration of NADF. Electrons receives chlorophyll photosystem II.

Exemplary total equation of photosynthesis light phase:

H 2 O + NADF + 2ADF + 2F → ½O 2 + NADF · H 2 + 2AF

Cyclic electron transport

The above describes the so-called non-cyclic light phase photosynthesis. Is there some more cyclic electron transport when the recovery of the NADF does not occur. At the same time, electrons from the photose system I go to the carrier chain, where the synthesis of ATP is. That is, this electron transport circuit receives electrons from the photosystem I, and not II. The first photo system as it realizes the cycle: it is returned to her emitted electrons. On the way, they spend part of their energy on the synthesis of ATP.

Photo phosphorylation and oxidative phosphorylation

The light phase of photosynthesis can be compared with the phase of cellular respiration - oxidative phosphorylation, which flows on mitochondrial cries. There, too, there is a synthesis of ATP due to the transfer of electrons and protons along the chain of carriers. However, in the case of photosynthesis, the energy is stored in ATP not for the needs of the cell, but mainly for the needs of the dark phase of photosynthesis. And if with breathing the initial source of energy serve organic substances, then with photosynthesis - sunlight. Synthesis ATF. With photosynthesis called photo phosphaelingrather than oxidative phosphorylation.

The dark phase of photosynthesis

For the first time, the dark phase of photosynthesis was studied in detail Calvin, Benson, Bassem. The reaction cycle opened by them was later called Calvin cycle, or C 3-photosynthesis. In certain groups of plants, a modified path of photosynthesis is observed - C 4, also called a hatch-sabra cycle.

In the dark reactions of photosynthesis, CO 2 fixation occurs. The dark phase proceeds in the stroma of chloroplast.

Recovery CO 2 occurs due to the energy of ATP and the rehabilitation force of the NADF · H 2 formed in light reactions. Without them, carbon fixation does not occur. Therefore, although the dark phase does not directly depend on the light, but usually also flows into the light.

Calvin cycle

The first phase response is the connection of CO 2 ( carboxylatione.) to 1,5-ribulosisobyphosphate ( ribulose-1,5-diphosphate) – Ribf. The latter is twice phosphorylated ribose. This reaction catalyzes the enzyme of ribulose-1,5-diphosphakarboxylase, also called rubysian.

As a result of carboxylation, an unstable hexagonal compound is formed, which, as a result of hydrolysis, disintegrates into two three-carbon molecules. phosphoglycerolic acid (FGK) - The first product of photosynthesis. FGK is also called phosphoglycerat.

RIBF + CO 2 + H 2 O → 2FGK

FGK contains three carbon atoms, one of which is included in the acid carboxyl group (-COOH):

FGK forms a three-carbon sugar (glyceraldehydphosphate) triosophosphate (TF)comprising an already aldehyde group (-CHO):

FGK (3-Acid) → TF (3-Sugar)

The activation of ATP and the reduction force of NAPF · H 2 is spent on this reaction. TF is the first carbohydrate photosynthesis.

After that, most of the trioseophosphate is spent on the regeneration of ribulosobiphosphate (RibF), which is again used to bind CO 2. Regeneration includes a number of responses that are spent with the costs of ATP, in which sucrosephosphates are involved with the number of carbon atoms from 3 to 7.

In such a cycle, the Ribf is Calvin's cycle.

From the Calvin cycle, there is a smaller part of the TF formed in it. In terms of 6 connected carbon dioxide molecules, the yield is 2 trioseophosphate molecules. Total cycle reaction with input and output products:

6CO 2 + 6H 2 O → 2TF

At the same time, in the binding, participating 6 RIBF molecules and 12 molecules of FGK are formed, which are converted to 12 TF, of which 10 molecules remain in the cycle and are converted to 6 RIBF molecules. Since TF is a three-carbon sugar, and the ribf is a pentaglion, then with respect to carbon atoms we have: 10 * 3 \u003d 6 * 5. The number of carbon atoms that provide the cycle does not change, the entire required Ribf is regenerated. And the six carbon dioxide molecules entered into the cycle are spent on the formation of two trioseophosphate molecules cycle.

The Calvin cycle per 6 connected CO 2 molecules is spent 18 ATP molecules and 12 NADF · H 2 molecules, which were synthesized in the reactions of the light phase of photosynthesis.

The calculation is carried out by two vehicle-phosphate molecules cycle, since the glucose molecule formed in the subsequent molecule includes 6 carbon atoms.

Triosophosphate (TF) is the final product of Calvin cycle, but it is difficult to name the final product of photosynthesis, since it is almost not accumulated, and, entering into reactions with other substances, turns into glucose, sucrose, starch, fats, fatty acids, amino acids. In addition to TF, FGK plays an important role. However, such reactions occur not only in photosynthetic organisms. In this sense, the dark phase of photosynthesis is the same as Calvin cycle.

From FGK by step enzymatic catalysis forms a six-curl sugar fructose-6-phosphatewhich turns into glucose. In glucose plants can be polymerized into starch and cellulose. Synthesis of carbohydrates is similar to the process of reverse Glycolize.

Photo

Oxygen suppresses photosynthesis. The larger O 2 in environmentThe even less effective is the process of binding CO 2. The fact is that the ribulosobiphosphate carboxylase enzyme (Rubisco) can react not only with carbon dioxide, but also oxygen. In this case, the dark reactions are somewhat different.

Phosphogiccolt is phosphoglycolic acid. It immediately clears the phosphate group, and it turns into glycolic acid (glycolate). For its "utilization" need oxygen again. Therefore, the larger in the oxygen atmosphere, the more it will stimulate photography and the more the plant will require oxygen to get rid of the reaction products.

Photocheate is a height-dependent consumption of oxygen and extraction of carbon dioxide. That is, the exchange of gases occurs as when breathing, but proceeds in chloroplasts and depends on the light radiation. From light, photography depends only because the ribulosobiphosphate is formed only during photosynthesis.

When photographes, the carbon atoms from glycolate in the Calvin cycle in the form of phosphoglycerolic acid (phosphoglycerat) occurs.

2 glycolat (C 2) → 2 glyoxylate (C 2) → 2 glycine (C 2) - CO 2 → Serine (C 3) → Hydroxypiruvat (C 3) → Glycerat (C 3) → FGK (C 3)

As can be seen, the refund is not complete, since one carbon atom is lost in converting two glycine molecules into one serine amino acid molecule, and carbon dioxide is released.

Oxygen is necessary at the stages of the conversion of glycolate in glyoxylate and glycine into serine.

The transformations of glycolate in glyoxylate, and then in glycine occur in peroxyms, serine synthesis in mitochondria. Serine enters peroxisoma again, where hydroxipruvate is first obtained from it, and then the glycerat. The glycerat enters the chloroplasts, where FGK is synthesized from it.

Photography is characteristic mainly for plants with C 3 -typ photosynthesis. It can be considered harmful because the energy is useless to transform the glycolate in FGK. Apparently photography arose due to the fact that the ancient plants were not ready for a large amount of oxygen in the atmosphere. Initially, their evolution was in an atmosphere rich in carbon dioxide, and it was he who mainly captured the Rubisco enzyme reaction center.

C 4 -Photosynthesis, or Cycle Hatch Slaka

If with C 3-phosynthesis, the first product of the dark phase is phosphoglycerinic acid, including three carbon atoms, then at C 4 - the first products are acids containing four carbon atoms: apple, oxide, asparagic.

With 4-photosynthesis, many tropical plants are observed, for example, sugar cane, corn.

C 4-tests are more efficiently absorbed carbon oxide, they have almost not expressed photography.

Plants in which the dark phase of photosynthesis proceeds in C 4-Puti, have a special structure of the sheet. In it, the conductive beams are surrounded by a double layer of cells. The inner layer is a conductive beam. Outer layer - Mesophyll cells. Chloroplasts of cells of the layers differ from each other.

For mesophilic chloroplast, large marriages are characteristic, high photos of the photosystems, the absence of the enzyme ribf carboxylase (rubysiso) and starch. That is, chloroplasts of these cells are adapted mainly for the light phase of photosynthesis.

In chloroplasts of cells of the conductive beam, the garnet is almost not developed, but the concentration of ribf carboxylase is high. These chloroplasts are adapted for the dark phase of photosynthesis.

Carbon dioxide first falls into mesophyll cells, binds to organic acids, in such a form is transported to the encoding cells, is released and further binds to both C 3-tests. That is, C 4 is complemented, and does not replace C 3.

In Mesophyll, CO 2 joins phosphoenolpiruvatuate (FEP) to form oxaloacetate (acid) comprising four carbon atoms:

The reaction occurs with the participation of the Fep-carboxylase enzyme, which has a higher affinity for CO 2 than Rubisco. In addition, FEP carboxylase does not interact with oxygen, which means it is not spent on photography. Thus, the advantage of C 4 -Photosynthesis is to more efficiently fix carbon dioxide, an increase in its concentration in the encoding cells and therefore more efficient operation of the ribf carboxylase, which is almost not spent on photography.

Oxaloacetate is converted to 4 carbon dicarboxylic acid (whale or aspartate), which is transported to chloroplasts of cage of conductive beams. Here the acid is decarboxylated (CO 2 exclusion), oxidizes (treated hydrogen) and turns into pyruvate. Hydrogen restores NADF. Pyruvate returns to the mesophyll, where the FEP is regenerated from it with the cost of ATP.

CO 2 broken in the chloroplasts of the plated cells goes to the usual C 3-Phase of the dark phase of photosynthesis, i.e. in the Calvin cycle.

Photosynthesis along the Hatch-Slaka path requires more energy consumption.

It is believed that C 4 appeared in evolution later C 3 and is largely a device against photography.