The totality of synthesis processes in a living organism. cell metabolism

The processes of plastic and energy exchange are inextricably linked. All synthetic (anabolic) processes require energy supplied during dissimilation reactions. The reactions of splitting (catabolism) themselves proceed only with the participation of enzymes synthesized in the process of assimilation.

The role of FTP in metabolism

The energy released during the breakdown of organic substances is not immediately used by the cell, but is stored in the form of high-energy compounds, usually in the form of adenosine triphosphate (ATP). By its chemical nature, ATP is a mononucleotide.

ATP (adenosine triphosphate)- a mononucleotide consisting of adenine, ribose and three phosphoric acid residues, interconnected by macroergic bonds.

These bonds store energy, which is released when they are broken:
ATP + H 2 O → ADP + H 3 PO 4 + Q 1
ADP + H 2 O → AMP + H 3 PO 4 + Q 2
AMP + H 2 O → adenine + ribose + H 3 PO 4 + Q 3,
where ATP is adenosine triphosphoric acid; ADP - adenosine diphosphoric acid; AMP - adenosine monophosphoric acid; Q 1 \u003d Q 2 \u003d 30.6 kJ; Q 3 \u003d 13.8 kJ.
The supply of ATP in the cell is limited and replenished through the process of phosphorylation. Phosphorylation- addition of a phosphoric acid residue to ADP (ADP + F → ATP). It occurs with varying intensity during respiration, fermentation, and photosynthesis. ATP is renewed extremely quickly (in humans, the lifespan of one ATP molecule is less than 1 minute).
The energy stored in ATP molecules is used by the body in anabolic reactions (biosynthesis reactions). The ATP molecule is the universal store and carrier of energy for all living beings.

energy exchange

The energy necessary for life, most organisms receive as a result of the oxidation of organic substances, that is, as a result of catabolic reactions. The most important compound acting as a fuel is glucose.
In relation to free oxygen, organisms are divided into three groups.

Classification of organisms in relation to free oxygen

In obligate aerobes and facultative anaerobes, in the presence of oxygen, catabolism proceeds in three stages: preparatory, oxygen-free, and oxygen. As a result, organic matter breaks down to organic compounds. In obligate anaerobes and facultative anaerobes, with a lack of oxygen, catabolism proceeds in the first two stages: preparatory and anoxic. As a result, intermediate organic compounds are formed, which are still rich in energy.

Stages of catabolism

1. The first stage is preparatory- consists in the enzymatic splitting of complex organic compounds into simpler ones. Proteins are broken down into amino acids, fats into glycerol and fatty acids, polysaccharides into monosaccharides, nucleic acids into nucleotides. In multicellular organisms, this occurs in gastrointestinal tract, in unicellular organisms - in lysosomes under the action of hydrolytic enzymes. The released energy is dissipated in the form of heat. The resulting organic compounds either undergo further oxidation or are used by the cell to synthesize its own organic compounds.
2. The second stage - incomplete oxidation (oxygen-free)- consists in the further splitting of organic substances, is carried out in the cytoplasm of the cell without the participation of oxygen. The main source of energy in the cell is glucose. Anoxic, incomplete oxidation of glucose is called glycolysis. As a result of glycolysis of one glucose molecule, two molecules of pyruvic acid (PVK, pyruvate) CH 3 COCOOH, ATP and water are formed, as well as hydrogen atoms, which are bound by the NAD + carrier molecule and stored in the form of NAD H.
The overall formula for glycolysis is as follows:
C 6 H 12 O 6 + 2H 3 PO 4 + 2ADP + 2NAD + → 2C 3 H 4 O 3 + 2H 2 O + 2ATP + 2NAD H.
Further in the absence of oxygen in the environment glycolysis products (PVK and NAD H) are processed either into ethyl alcohol - alcoholic fermentation(in yeast and plant cells with a lack of oxygen)
CH 3 COCOOH → CO 2 + CH 3 SON
CH 3 SON + 2NAD H → C 2 H 5 OH + 2NAD +,
or into lactic acid - lactic acid fermentation (in animal cells with a lack of oxygen)
CH 3 COCOOH + 2NAD H → C 3 H 6 O 3 + 2NAD +.
In the presence of oxygen in the environment glycolysis products undergo further cleavage to final products.
3. The third stage - complete oxidation (respiration)- consists in the oxidation of PVC to carbon dioxide and water, is carried out in mitochondria with the obligatory participation of oxygen.
It consists of three stages:
A) the formation of acetylcoenzyme A;
B) oxidation of acetyl coenzyme A in the Krebs cycle;
C) oxidative phosphorylation in the electron transport chain.

A. At the first stage, PVA is transferred from the cytoplasm to the mitochondria, where it interacts with matrix enzymes and forms 1) carbon dioxide, which is excreted from the cell; 2) hydrogen atoms, which are delivered by carrier molecules to the inner membrane of the mitochondria; 3) acetyl coenzyme A (acetyl-CoA).
B. At the second stage, acetylcoenzyme A is oxidized in the Krebs cycle. The Krebs cycle (tricarboxylic acid cycle, citric acid cycle) is a chain of successive reactions during which 1) two molecules of carbon dioxide, 2) an ATP molecule and 3) four pairs of hydrogen atoms are formed from one molecule of acetyl-CoA, and 3) four pairs of hydrogen atoms are transferred to molecules - carriers - OVER and FAD. Thus, as a result of glycolysis and the Krebs cycle, the glucose molecule is broken down to CO 2, and the energy released in this case is spent on the synthesis of 4 ATP and accumulates in 10 NAD H and 4 FAD H 2.
C. In the third stage, hydrogen atoms with NADH and FAD H 2 are oxidized by molecular oxygen O 2 to form water. One NAD H is able to form 3 ATP, and one FAD H 2 -2 ATP. Thus, the energy released in this case is stored in the form of another 34 ATP.
This process proceeds as follows. Hydrogen atoms are concentrated near the outer side of the inner mitochondrial membrane. They lose electrons, which are transferred along the chain of carrier molecules (cytochromes) of the electron transport chain (ETC) to the inner side of the inner membrane, where they combine with oxygen molecules:
O 2 + e - → O 2 -.
As a result of the activity of the enzymes of the electron transport chain, the inner membrane of mitochondria is negatively charged from the inside (due to O 2 -), and from the outside it is positively charged (due to H +), so that a potential difference is created between its surfaces. Molecules of the enzyme ATP synthetase with an ion channel are built into the inner membrane of mitochondria. When the potential difference across the membrane reaches a critical level, the positively charged particles H + force electric field begin to push through the ATPase channel and, once on the inner surface of the membrane, interact with oxygen, forming water:
1/2O 2 - + 2H + → H 2 O.
The energy of hydrogen ions H + transported through the ion channel of the inner membrane of the mitochondria is used to phosphorylate ADP to ATP:
ADP + F → ATP.
This formation of ATP in mitochondria with the participation of oxygen is called oxidative phosphorylation.
The overall equation for the breakdown of glucose in the process of cellular respiration:
C 6 H 12 O 6 + 6O 2 + 38H 3 PO 4 + 38ADP → 6CO 2 + 44H 2 O + 38ATP.
Thus, during glycolysis, 2 ATP molecules are formed, during cellular respiration - another 36 ATP molecules, in general, with complete oxidation of glucose - 38 ATP molecules.

plastic exchange

Plastic exchange, or assimilation, is a set of reactions that ensure the synthesis of complex organic compounds from simpler ones (photosynthesis, chemosynthesis, protein biosynthesis, etc.).

Heterotrophic organisms build their own organic matter from organic food components. Heterotrophic assimilation essentially boils down to rearrangement of molecules:
organic food substances (proteins, fats, carbohydrates) → simple organic molecules (amino acids, fatty acids, monosaccharides) → macromolecules of the body (proteins, fats, carbohydrates).
Autotrophic organisms are capable of completely independently synthesizing organic substances from inorganic molecules consumed from the external environment. In the process of photo- and chemosynthesis, the formation of simple organic compounds occurs, from which macromolecules are subsequently synthesized:
inorganic substances (CO 2, H 2 O) → simple organic molecules (amino acids, fatty acids, monosaccharides) → macromolecules of the body (proteins, fats, carbohydrates).

Photosynthesis

Photosynthesis- synthesis of organic compounds from inorganic ones due to the energy of light. The overall photosynthesis equation is:

Photosynthesis takes place with the participation photosynthetic pigments, which have the unique property of converting the energy of sunlight into the energy of a chemical bond in the form of ATP. Photosynthetic pigments are protein-like substances. The most important pigment is chlorophyll. In eukaryotes, photosynthetic pigments are embedded in the inner membrane of plastids, in prokaryotes, in invaginations of the cytoplasmic membrane.
The structure of the chloroplast is very similar to that of the mitochondria. The inner membrane of thylakoid gran contains photosynthetic pigments, as well as proteins of the electron transport chain and molecules of the enzyme ATP synthetase.
The process of photosynthesis consists of two phases: light and dark.
1. Light phase of photosynthesis proceeds only in the light in the membrane of the thylakoids of the grana.
It includes the absorption of light quanta by chlorophyll, the formation of an ATP molecule, and the photolysis of water.
Under the action of a light quantum (hv), chlorophyll loses electrons, passing into an excited state:

These electrons are transferred by carriers to the outer, that is, the surface of the thylakoid membrane facing the matrix, where they accumulate.
At the same time, photolysis of water occurs inside the thylakoids, that is, its decomposition under the action of light:

The resulting electrons are transferred by carriers to chlorophyll molecules and restore them. The chlorophyll molecules return to a stable state.
Hydrogen protons, formed during the photolysis of water, accumulate inside the thylakoid, creating an H + -reservoir. As a result, the inner surface of the thylakoid membrane is charged positively (due to H +), and the outer surface is negatively charged (due to e -). As oppositely charged particles accumulate on both sides of the membrane, the potential difference increases. When the critical value of the potential difference is reached, the strength of the electric field begins to push protons through the ATP synthetase channel. The energy released in this case is used to phosphorylate ADP molecules:
ADP + F → ATP.

The formation of ATP during photosynthesis under the influence of light energy is called photophosphorylation.
Hydrogen ions, once on the outer surface of the thylakoid membrane, meet electrons there and form atomic hydrogen, which binds to the hydrogen carrier molecule NADP (nicotinamide adenine dinucleotide phosphate):
2H + + 4e - + NADP + → NADP H 2.
Thus, during the light phase of photosynthesis, three processes occur: the formation of oxygen due to the decomposition of water, the synthesis of ATP, and the formation of hydrogen atoms in the form of NADP·H 2 . Oxygen diffuses into the atmosphere, while ATP and NADP H 2 participate in the processes of the dark phase.
2. Dark phase of photosynthesis proceeds in the chloroplast matrix both in the light and in the dark and is a series of successive transformations of CO 2 coming from the air in the Calvin cycle. The reactions of the dark phase are carried out due to the energy of ATP. In the Calvin cycle, CO 2 binds with hydrogen from NADP·H 2 to form glucose.
In the process of photosynthesis, in addition to monosaccharides (glucose, etc.), monomers of other organic compounds are synthesized - amino acids, glycerol and fatty acids. Thus, thanks to photosynthesis, plants provide themselves and all life on Earth with the necessary organic substances and oxygen.
Comparative characteristics photosynthesis and respiration of eukaryotes is presented in the table.

Comparative characteristics of photosynthesis and respiration of eukaryotes

Genetic information in all organisms is stored in the form of a specific sequence of DNA nucleotides (or RNA for RNA-containing viruses). Prokaryotes contain genetic information in the form of a single DNA molecule. In eukaryotic cells, the genetic material is distributed in several DNA molecules organized into chromosomes.
DNA consists of coding and non-coding regions. Coding regions code for RNA. Non-coding regions of DNA perform structural function, allowing regions of genetic material to be packaged in a particular way, or regulatory function, participating in the inclusion of genes that direct protein synthesis.
Genes are the coding regions of DNA. Gene - a section of a DNA molecule encoding the synthesis of one mRNA (and, accordingly, a polypeptide), rRNA or tRNA.
The region of the chromosome where the gene is located is called locus . The set of genes in the cell nucleus is genotype , the totality of genes of the haploid set of chromosomes - genome , a set of extranuclear DNA genes (mitochondria, plastids, cytoplasm) - plasmon .
The implementation of the information recorded in the genes through the synthesis of proteins is called expression (manifestation) of genes. Genetic information is stored in the form of a certain sequence of DNA nucleotides, and is realized in the form of a sequence of amino acids in a protein. RNA mediates and carries information. That is, the implementation of genetic information occurs as follows:
DNA → RNA → protein.
This process is carried out in two stages:
1) transcription;
2) broadcast.

Transcription(from lat. transcription- rewriting) - the synthesis of RNA using DNA as a template. As a result, mRNA, tRNA and rRNA are formed. The transcription process requires a large expenditure of energy in the form of ATP and is carried out by the enzyme RNA polymerase.

At the same time, not the entire DNA molecule is transcribed, but only its individual segments. Such a segment ( transcripton) starts promoter- a section of DNA where RNA polymerase attaches and where transcription begins and ends terminator a segment of DNA containing a signal for the end of transcription. A transcripton is a gene in terms of molecular biology.
Transcription, like replication, is based on the ability of the nitrogenous bases of nucleotides to complementary binding. At the time of transcription, the DNA double strand is broken, and RNA synthesis is carried out along one DNA strand.

During transcription, the DNA nucleotide sequence is transcribed onto the synthesized mRNA molecule, which acts as a template in the process of protein biosynthesis.
The genes of prokaryotes consist only of coding nucleotide sequences.

Eukaryotic genes consist of alternating coding ( exons) and non-coding ( introns) plots.

After transcription, mRNA regions corresponding to introns are removed during splicing, which is an integral part of processing.

Processing- the process of formation of mature mRNA from its precursor pre-mRNA. It includes two main events. 1. Attachment to the ends of mRNA short sequences of nucleotides, indicating the start and end of translation. Splicing- removal of non-informative mRNA sequences corresponding to DNA introns. As a result of splicing, the molecular weight of mRNA is reduced by 10 times. Broadcast(from lat. translation- translation) - the synthesis of a polypeptide chain using mRNA as a template.

All three types of RNA are involved in translation: mRNA is the information matrix; tRNAs deliver amino acids and recognize codons; rRNA together with proteins form ribosomes that hold mRNA, tRNA and protein and carry out the synthesis of the polypeptide chain.

Broadcast stages

Matrix synthesis reactions. Matrix synthesis reactions include

• self-duplication of DNA (replication);
• the formation of mRNA, tRNA and rRNA on a DNA molecule (transcription);
• protein biosynthesis to mRNA (translation).

All these reactions are united by the fact that a DNA molecule in one case or an mRNA molecule in another act as a template on which identical molecules are formed. Matrix synthesis reactions are the basis of the ability of living organisms to reproduce their own kind.
Regulation of gene expression. The body of a multicellular organism is built from a variety of cell types. They differ in structure and function, that is, they are differentiated. The differences are manifested in the fact that in addition to the proteins necessary for any cell of the body, cells of each type also synthesize specialized proteins: keratin is formed in the epidermis, hemoglobin is formed in erythrocytes, etc. Cell differentiation is due to a change in the set of expressed genes and is not accompanied by any irreversible changes in the structure of the DNA sequences themselves.

During which various substances are included in its composition. Synthesis of macromolecular compounds (proteins, nucleic acids, polysaccharides, lipids). Impossible without energy

In the course of assimilation, simple substances (complex ones are initially broken down into simple ones), non-specific for any organism, turn into complex compounds characteristic of this type of compound (assimilated).

Assimilation is balanced by the sum of dissimilation (decay) processes.

see also

Links

• // Encyclopedic Dictionary of Brockhaus and Efron: In 86 volumes (82 volumes and 4 additional). - St. Petersburg. , 1890-1907.

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See what "Assimilation (biology)" is in other dictionaries:

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The concept of living matter was introduced by V.I. Vernadsky. He called living matter the totality of the masses of all organisms. The living world is extremely diverse. To date, biologists have described more than a million species of living organisms. The mass of living matter on the planet is estimated at 10 13 ... 10 14 tons. Each organism is a set of orderly interacting structures that form a single whole, called system. In living systems, processes proceed continuously in complex sequential and parallel chemical reactions, which result in growth, division, nutrition, isolation of cells, as well as their movement and interaction with each other.

In biochemistry, the entire set of chemical transformations in a living organism is united by the concept metabolism (metabolism). Organic substances of non-living origin are called abiogenic substances, and metabolic products are called biogenic substances.

The distinguishing features of a living object are the following.

• 1. High organization with a complex internal structure. Any component of the body has a special purpose and performs certain functions (cellular structure and specificity of body cells).
• 2. The ability to self-reproduce (growth, reproduction).
• 3. The ability to extract, transform and use the energy of the environment.
• 4. The ability to "learn" (a term that means both the ability to respond to the impact of the environment, change, adapting to its conditions, and the acquisition of new skills and properties under the influence of these conditions - adaptation, development).
• 5. The ability of a living organism to maintain a constant composition of the internal environment despite drastic changes in external conditions.

Biochemical transformations perform the following main functions:

• 1) supply of chemical energy due to the breakdown of energy-rich food substances;
• 2) the transformation of food molecules into building blocks used in subsequent metabolic processes to build cellular components (macromolecules);
• 3) assembly of cellular components (proteins, nucleic acids, lipids, polysaccharides, etc.);
• 4) synthesis and destruction of biomolecules that perform specific cell functions.

Living cells maintain their internal order in a dynamic stationary state due to substances and free energy coming from the external environment and being transformed in the process of metabolism.

For the synthesis of organic substances, living organisms use inorganic substances: water, carbon dioxide, ammonia, salts. The differences between plants and animals lie in the fact that in animals such synthesis occurs in much smaller volumes, since a number of substances enter their body already in a “ready-made” form.

Living organisms are capable of synthesizing a large number of fatty and aromatic compounds. Organic molecules that have three carbon atoms in their composition participate in the synthesis of carbohydrates in the body: molecules of lactic acid, pyruvic acid, glycerol, etc. These substances are called glycogen formers, since with their participation in the liver there is a synthesis of glycogen.

From the products of the transformation of carbohydrates in the body, fats are formed. From the intermediate products of the conversion of carbohydrates and fats, some a-keto acids are synthesized: oxaloacetic, a-ketoglutaric, pyruvic, and others. a-Keto acids, adding ammonia, are converted into the corresponding amino acids. However, in animal organisms, not all amino acids necessary for life activity are synthesized. The complete set of amino acids required for the formation of proteins is synthesized only in green plants. Animal organisms are capable of synthesizing only certain cyclic compounds, such as cholesterol, the main "building" material of which is acetic acid. The human body cannot synthesize a "simple" molecule having a benzene ring, but easily synthesizes heterocyclic compounds - derivatives of purine, pyrimidine and pyrrole. The starting materials for the synthesis of purine are the molecules of glycine, carbon dioxide, formic acid and glutamine. Carbamic and succinic acids are involved in the synthesis of pyrimidine.

All living organisms are divided into two groups depending on the method of assimilation of carbon coming from the environment.

autotrophic Cells use carbon dioxide (CO2) as their sole source of carbon, from which they build carbon-containing biomolecules. Photosynthetic bacteria and green plant cells belong to this group.

Heterotrophic cells receive carbon in the form of fairly complex organic compounds, such as glucose. These include animal cells and most microorganisms.

In the biosphere, autotrophs and heterotrophs coexist as members of a single cycle in which carbon and oxygen are continuously cycled between the animal and plant worlds(Fig. 1.1). The source of energy for this process is the Sun.

Rice. 1.1.

In addition to carbon, oxygen and energy, all living organisms need nitrogen. Nitrogen is required for the synthesis of amino acids, purine and pyrimidine bases. Of the 20 essential amino acids a person receives "ready" from food, only 10, which the body is not able to synthesize itself. Plants can synthesize all amino acids from nitrogen and its compounds. Since the main amount of nitrogen (80%) is contained in gaseous form (N2), all living things ultimately depend on organisms capable of fixing it. Nitrogen is fixed, for example, by cyanobacteria (blue-green algae). They lead an independent existence, since they are completely autotrophic, that is, they absorb nitrogen, carbon dioxide and are capable of photosynthesis. Nitrogen-fixing bacteria usually live in the soil. Some of them exist as symbionts on the root nodules of plants. Nitrifying bacteria oxidize ammonia to nitrites and nitrates, while denitrifying bacteria convert nitrates back to ammonia. Thus, nitrogen, like carbon and oxygen, makes a continuous cycle (Fig. 1.2).

Rice.

All metabolic processes - chain, and they can be subdivided into biosynthetic chains ( anabolism) and chains of degradation (catabolism).

Chain processes (reactions) can be represented as follows:

Chain reactions form networks consisting of both assimilation (synthesis) and dissimilation (decay) processes.

Assimilation - anabolism- accumulation, consumption, synthesis - is associated with growth and development. Dissimilation - catabolism- isolation, decay, destruction (chemical breakdown) - is associated, in particular, with the aging of the body and the death of any organs in the process of life, resorption.

Assimilation and dissimilation processes are interconnected in such a way that the constancy of the internal environment in the body is maintained in all respects to ensure normal life in the environment.

The dynamic constancy of the internal environment (blood, lymph, tissue fluid) and the stability of the basic physiological functions (circulation, respiration, thermoregulation, metabolism, etc.) of the human and animal body are called homeostasis.

The minimum amount of substances necessary to maintain the life of a person in a state of rest is called main exchange. For example, in the human body to ensure the basic metabolism, it is required to introduce 100 g of protein per day.

Cell metabolism - it is a system of enzymatic transformations of both substances and energy, starting from the initial substances and ending with the biosynthesis of living matter. The simplest units of metabolic activity are enzymes, each of which, as a rule, catalyzes any one chemical reaction. Since metabolic processes are sequential transformations, we can speak of multi-enzyme systems acting together in a certain sequence.

Most enzymes are water soluble globular proteins, structural proteins of the cell can also have catalytic properties.