Metabolism and energy conversion protein biosynthesis. Metabolism and energy conversion

1. Give definitions of concepts.
Metabolism- a set of chemical reactions that occur in a living organism to maintain life.
Energy metabolism - the process of metabolic breakdown, decomposition into simpler substances or oxidation of a substance, usually occurring with the release of energy in the form of heat and in the form of ATP.
Plastic exchange – the totality of all biosynthetic processes occurring in living organisms.

2. Fill out the table.

3. Draw a schematic diagram of the ATP molecule. Label its parts. Indicate the location of high-energy bonds. Write the full name of this molecule.
ATP – adenosine triphosphoric acid

4. What class of organic substances does ATP belong to? Why did you come to this conclusion?
Nucleotide, as it consists of adenine, ribose and three phosphoric acid residues.

5. Using the material in § 3.2, fill out the table.

6. What is the biological role of the stepwise nature of energy metabolism?
The gradual release of energy during energy metabolism allows for more efficient use and storage of energy. With a one-time release of such an amount of energy, most of it would simply not have time to combine with ADP and would be released as heat, which means large losses for the body.

7. Explain why oxygen is necessary for most modern organisms. What process produces carbon dioxide in cells?
Oxygen is necessary for breathing. In the presence of oxygen, organic substances are completely oxidized during respiration to carbon dioxide and water.

8. How did the accumulation of oxygen in the Earth’s atmosphere affect the intensity of the life processes of the inhabitants of our planet?
Oxygen has a profound effect on the body as a whole, increasing the overall vital energy of the inhabitants of our planet. New organisms arose and evolved.

9. Fill in the missing words.
Plastic exchange reactions occur with the absorption of energy.
Energy metabolism reactions occur with the release of energy.
The preparatory stage of energy metabolism takes place in the gastrointestinal tract and lysosomes
cells.
Glycolysis occurs in the cytoplasm.
During the preparatory stage, proteins are converted into amino acids by digestive enzymes.

10. Choose the correct answer.
Test 1.
Which abbreviation denotes the carrier of energy in a living cell?
3) ATP;

Test 2.
At the preparatory stage of energy metabolism, proteins break down to:
2) amino acids;

Test 3.
As a result of oxygen-free oxidation in animal cells with a lack of oxygen, the following is formed:
3) lactic acid;

Test 4.
Energy that is released in the reactions of the preparatory stage of energy metabolism:
2) dissipates in the form of heat;

Test 5.
Glycolysis is provided by enzymes:
3) cytoplasm;

Test 6.
The complete oxidation of four glucose molecules produces:
4) 152 ATP molecules.

Test 7.
For the fastest possible recovery from fatigue during exam preparation, it is best to eat:
3) a piece of sugar;

11. Make up a syncwine for the term “metabolism”.
Metabolism
Plastic and energetic.
Synthesizes, destroys, transforms.
A set of chemical reactions in a living organism to maintain life.
Metabolism.

12. Metabolic rate is not constant. Indicate some external and internal reasons that, in your opinion, can change the metabolic rate.
External – ambient temperature, physical activity, body weight.
Internal – the level of hormones in the blood, the state of the nervous system (suppression or excitation).

13. You know that there are aerobic and anaerobic organisms. What are facultative anaerobes?
These are organisms whose energy cycles follow an anaerobic path, but are able to exist with the access of oxygen, in contrast to obligate anaerobes, for which oxygen is destructive.

14. Explain the origin and general meaning of the word (term), based on the meaning of the roots that make it up.

15. Select a term and explain how its modern meaning matches the original meaning of its roots.
The chosen term is glycolysis.
Correspondence: The term matches but is complemented. The modern definition of glycolysis is not just the “breakdown of sweets,” but the process of glucose oxidation, in which two PVK molecules are formed from one molecule, carried out sequentially through several enzymatic reactions and accompanied by the storage of energy in the form of ATP and NADH.

16. Formulate and write down the main ideas of § 3.2.
Any organism is characterized by a metabolism - a set of chemicals. reactions to maintain life. Energy metabolism is the process of decomposition into simpler substances, which occurs with the release of energy in the form of heat and in the form of ATP. Plastic metabolism is the totality of all biosynthetic processes occurring in living organisms.
The ATP molecule is a universal energy supplier in cells.
Energy metabolism occurs in 3 stages: the preparatory stage (glucose and heat are formed), glycolysis (PVC, 2 ATP molecules and heat are formed) and oxygen, or cellular respiration (36 ATP molecules and carbon dioxide are formed).

All living organisms on Earth are open systems capable of actively organizing the supply of energy and matter from the outside. Energy is necessary for vital processes, but primarily for the chemical synthesis of substances used to build and restore the structures of cells and the body. Living beings are capable of using only two types of energy: light(solar radiation energy) and chemical(energy of bonds of chemical compounds) - on this basis, organisms are divided into two groups - phototrophs and chemotrophs.

The main source of structural molecules is carbon. Depending on their carbon sources, living organisms are divided into two groups: autotrophs, which use an inorganic carbon source (carbon dioxide), and heterotrophs, which use organic carbon sources.

The process of consuming energy and matter is called food. Two methods of nutrition are known: holozoic - through the capture of food particles inside the body and holophytic - without capture, through the absorption of dissolved nutrients through the surface structures of the body. Nutrients that enter the body are involved in metabolic processes.

Metabolism is a set of interconnected and balanced processes that include a variety of chemical transformations in the body. Synthesis reactions carried out with energy consumption form the basis of anabolism (plastic metabolism or assimilation).

Splitting reactions accompanied by the release of energy form the basis catabolism(energy exchange or dissimilation).

1. The importance of ATP 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 and consists of the nitrogenous base adenine, the carbohydrate ribose and three phosphoric acid residues.

The energy released during ATP hydrolysis is used by the cell to perform all types of work. Significant amounts of energy are spent on biological synthesis. ATP is a universal source of cell energy. The supply of ATP in the cell is limited and is replenished due to the process of phosphorylation, which occurs at varying rates during respiration, fermentation and photosynthesis. ATP is renewed extremely quickly (in humans, the lifespan of one ATP molecule is less than 1 minute).

2. Energy metabolism in the cell. ATP synthesis

ATP synthesis occurs in the cells of all organisms in the process of phosphorylation, i.e. addition of inorganic phosphate to ADP. The energy for phosphorylation of ADP is generated during energy metabolism. Energy metabolism, or dissimilation, is a set of reactions of the breakdown of organic substances, accompanied by the release of energy. Depending on the habitat, dissimilation can occur in two or three stages.

In most living organisms - aerobes living in an oxygen environment - three stages are carried out during dissimilation: preparatory, oxygen-free, oxygen. In anaerobes living in an environment deprived of oxygen, or in aerobes with a lack of it, dissimilation occurs only in the first two stages with the formation of intermediate organic compounds that are still rich in energy.

The first stage - preparatory - consists of the enzymatic breakdown of complex organic compounds into simpler ones (proteins into amino acids; polysaccharides into monosaccharides; nucleic acids into nucleotides). Intracellular breakdown of organic substances occurs under the action of hydrolytic enzymes of lysosomes. The energy released in this case is dissipated in the form of heat, and the resulting small organic molecules can undergo further breakdown and be used by the cell as “building material” for the synthesis of its own organic compounds.

The second stage - incomplete oxidation - occurs directly in the cytoplasm of the cell, does not require the presence of oxygen and consists of further breakdown of organic substrates. The main source of energy in the cell is glucose. The oxygen-free, incomplete breakdown of glucose is called glycolysis.

The third stage - complete oxidation - occurs with the obligatory participation of oxygen. As a result, the glucose molecule is broken down into inorganic carbon dioxide, and the energy released in this case is partially spent on the synthesis of ATP.

3. Plastic exchange

Plastic metabolism, or assimilation, is a set of reactions that ensure the synthesis of complex organic compounds in the cell. Heterotrophic organisms build their own organic matter from organic food components. Heterotrophic assimilation is essentially reduced to the rearrangement of molecules.

Organic substances of food (proteins, fats, carbohydrates) --> digestion --> Simple organic molecules (amino acids, fatty acids, monosaccharides) --> biological syntheses --> 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 autotrophic assimilation, the reactions of photo- and chemosynthesis, which ensure the formation of simple organic compounds, precede the biological syntheses of macromolecules:

Inorganic substances (carbon dioxide, water) --> photosynthesis, chemosynthesis --> Simple organic molecules (amino acids, fatty acids, monosaccharides) -----biological syntheses --> Body macromolecules (proteins, fats, carbohydrates)

4. Photosynthesis

Photosynthesis is the synthesis of organic compounds from inorganic ones, using the energy of the cell. The leading role in the processes of photosynthesis is played by photosynthetic pigments, which have the unique property of capturing light and converting its energy into chemical energy. Photosynthetic pigments are a fairly large group of protein-like substances. The main and most important energy-wise is pigment. chlorophyll a, found in all phototrophs except photosynthetic bacteria. Photosynthetic pigments are embedded in the inner membrane of plastids in eukaryotes or in invaginations of the cytoplasmic membrane in prokaryotes.

During the process of photosynthesis, in addition to monosaccharides (glucose, etc.), which are converted into starch and stored by the plant, monomers of other organic compounds are synthesized - amino acids, glycerol and fatty acids. Thus, thanks to photosynthesis, plant cells, or more precisely, chlorophyll-containing cells, provide themselves and all living things on Earth with the necessary organic substances and oxygen.

5. Chemosynthesis

Chemosynthesis is also the process of synthesizing organic compounds from inorganic ones, but it is carried out not at the expense of light energy, but at the expense of chemical energy obtained from the oxidation of inorganic substances (sulfur, hydrogen sulfide, iron, ammonia, nitrite, etc.). The most important are nitrifying, iron and sulfur bacteria.

The energy released during oxidation reactions is stored by bacteria in the form of ATP and used for the synthesis of organic compounds. Chemosynthetic bacteria play a very important role in the biosphere. They participate in wastewater treatment, contribute to the accumulation of minerals in the soil, and increase soil fertility.

DNA - biopolymer, micromolecule, polynucleotide, -manomer-nucleotide Nitrogen bases - deoxyribose - phosphoric acid residue Nitrogen bases: adenine, thymine, guanine, cytosine - double-stranded structure of RNA - biopolymer, macromolecule, polynucleotide, - manomer - nucleotide Nitrogen bases - Ribose - Phosphoric acid residue Nitrogen bases: adenine, uracil, guanine, cytosine. The RNA molecule is single-stranded. Functions: DNA - storage of genetic information RNA - transmission of genetic information

Messenger RNA, which carries information about the primary structure of protein molecules, is synthesized in the nucleus. Having passed through the pores of the nuclear membrane, the mRNA is sent to the ribosomes, where the genetic information is deciphered - translated from the Language of Nucleotides to the Language of Amino Acids.

Amino acids from which proteins are synthesized are delivered to ribosomes using special RNAs called transfer RNAs (t-RNAs). In t-RNA, the sequence of three nucleotides is complementary to the nucleotides of the codon in i-RNA. This sequence of nucleotides in the tRNA structure is called an anticodon. Each tRNA attaches a specific amino acid, using enzymes and using ATP. This is the first stage of synthesis.

In order for an amino acid to be included in a protein chain, it must break away from the tRNA. At the second stage of protein synthesis, tRNA acts as a translator from the Language of Nucleotides to the Language of Amino Acids. This translation occurs on the ribosome. There are two sections in it: on one, the t-RNA receives a command from the mRNA - the anticodon recognizes the codon, on the other, the order is executed - the amino acid is torn off from the t-RNA.

The third stage of protein synthesis is that the enzyme synthetase attaches the amino acid detached from the tRNA to the growing protein molecule. Messenger RNA continuously slides along the ribosome, each triplet first falls into the first section, where it is recognized by the tRNA anticodon, then to the second section. The t-RNA with an amino acid attached to it also goes here; here the amino acids are separated from the t-RNA and connected to each other in the sequence in which triplets follow one after another.

When one of the three triplets, which are punctuation marks between genes, appears on the ribosome in the first section, this means that protein synthesis is complete. The finished protein chain leaves the ribosome. The process of protein synthesis requires a lot of energy. The connection of each amino acid with t-RNA requires the energy of one ATP molecule.

To increase protein production, mRNA often simultaneously passes through not one, but several ribosomes in succession. Such a structure, united by one mRNA molecule, is called a polysome. On each ribosome, in a conveyor belt similar to a string of beads, several molecules of identical proteins are sequentially synthesized.

Protein synthesis on ribosomes is called translation. The synthesis of protein molecules occurs continuously and occurs at high speed: from 50 to 60 thousand peptide bonds are formed in one minute. The synthesis of one protein molecule lasts only 3-4 seconds. Each stage of biosynthesis is catalyzed by appropriate enzymes and supplied with energy through the breakdown of ATP. Synthesized proteins enter the endoplasmic reticulum channels, through which they are transported to certain parts of the cell.

Plant cell as an osmotic system

The plant cell is an osmotic system. The cell sap of the vacuole is a highly concentrated solution. The osmotic pressure of cell sap is designated -.

To enter the vacuole, water must pass through the cell wall, plasmalemma, cytoplasm, and tonoplast. The cell wall is highly permeable to water. The plasmalemma and tonoplast have selective permeability. Therefore, a plant cell can be considered as an osmotic system, in which the plasma membrane and tonoplast are a semi-permeable membrane, and the vacuole with cell sap is a concentrated solution. Therefore, if a cell is placed in water, then water, according to the laws of osmosis, will begin to flow into the cell.

The force with which water enters the cell is called suction force - S.

It is identical to water potential.

As water enters the vacuole, its volume increases, the water dilutes the cell sap, and the cell walls begin to experience pressure. The cell wall has a certain elasticity and can stretch.

With an increase in the volume of the vacuole, the cytoplasm is pressed against the cell wall and turgor pressure appears on the cell wall (P). At the same time, an equal amount of counterpressure from the cell wall on the protoplast arises from the cell wall. The back pressure of the cell wall is called pressure potential (-P).

Thus, the magnitude of the suction force S is determined by the osmotic pressure of the cell sap and the turgor hydrostatic pressure of the cell P, which is equal to the back pressure of the cell wall that occurs when it is stretched -P.

S = - P or - - .

If the plant is in conditions of sufficient soil and air moisture, then the cells are in a state of complete turgor. When a cell is completely saturated with water (turgescent), then its suction force is zero S = 0, and the turgor pressure is equal to the potential osmotic pressure P =.

When there is a lack of moisture in the soil, water deficiency first occurs in the cell wall. The water potential of the cell wall becomes lower than in the vacuole, and water begins to move from the vacuole into the cell wall. The outflow of water from the vacuole reduces turgor pressure in the cells and increases their suction force. With a prolonged lack of moisture, most cells lose turgor, and the plant begins to wither, losing elasticity and firmness. In this case, turgor pressure P = 0, and suction force S =

If, due to a very large loss of water, the turgor pressure drops to zero, the leaf will wither completely. Further loss of water will lead to the death of the cell protoplast. An adaptive feature to a sudden loss of water is the rapid closure of stomata when there is a lack of moisture.

Cells can quickly restore turgor if the plant receives enough water or at night when the plant receives enough water from the soil. And also when watering.

Water potential; equals 0 for pure water; equals 0 or negative for cells.

Osmotic potential is always negative

Pressure potential; usually positive in living cells (in cells whose contents are under pressure), but negative in xylem cells (in which water tension is created).

Total result of the action

With full turgor

During initial plasmolysis

If you place a cell in a hypertonic solution with a lower water potential, then water begins to leave the cell by osmosis through the plasma membrane. First, water will leave the cytoplasm, then through the tonoplast from the vacuole. The living contents of the cell, the protoplast, shrink and fall behind the cell wall. A process is taking place plasmolysis. The space between the cell wall and the protoplast is filled with an external solution. Such a cell is called plasmolyzed. Water will leave the cell until the water potential of the protoplast becomes equal to the water potential of the surrounding solution, after which the cell stops shrinking. This process is reversible and the cell does not receive damage.

If the cell is placed in clean water or a hypotonic solution, then the turgor state of the cell is restored and the process deplasmolysis.

Under conditions of water deficiency in young tissues, a sharp increase in water loss leads to the fact that the turgor pressure of the cell becomes negative and the protoplast, contracting in volume, does not separate from the cell wall, but pulls it along with it. Cells and tissues shrink. This phenomenon is called cytorhiz.

Metabolism of substances and energy (metabolism) occurs at all levels of the body: cellular, tissue and organismal. It ensures the constancy of the internal environment of the body - homeostasis - in continuously changing conditions of existence. Two processes occur simultaneously in a cell: plastic metabolism (anabolism or assimilation) and energy metabolism (fatabolism or dissimilation).

Plastic metabolism is a set of biosynthesis reactions, or the creation of complex molecules from simple ones. The cell constantly synthesizes proteins from amino acids, fats from glycerol and fatty acids, carbohydrates from monosaccharides, nucleotides from nitrogenous bases and sugars. These reactions require energy. The energy used is released through energy exchange. Energy metabolism is a set of reactions that break down complex organic compounds into simpler molecules. Part of the energy released in this case goes to the synthesis of ATP (adenosine triphosphoric acid) molecules rich in energy bonds. The breakdown of organic substances occurs in the cytoplasm and mitochondria with the participation of oxygen. The reactions of assimilation and dissimilation are closely related to each other and the external environment. The body receives nutrients from the external environment. Waste substances are released into the external environment.

Enzymes (enzymes) are specific proteins, biological catalysts that accelerate metabolic reactions in the cell. All processes in a living organism are carried out directly or indirectly with the participation of enzymes. An enzyme catalyzes only one reaction or acts on only one type of bond. This ensures fine regulation of all vital processes (respiration, digestion, photosynthesis, etc.) occurring in the cell or body. In the molecule of each enzyme there is a site that makes contact between the molecules of the enzyme and a specific substance (substrate). The active center of the enzyme is a functional group (for example, OH - serine group) or a separate amino acid.

The rate of enzymatic reactions depends on many factors: temperature, pressure, acidity of the environment, the presence of inhibitors, etc.

Stages of energy metabolism:

• Preparatory- occurs in the cytoplasm of cells. Under the action of enzymes, polysaccharides are broken down into monosaccharides (glucose, fructose, etc.), fats are broken down into glycerol and fatty acids, proteins into amino acids, and nucleic acids into nucleotides. This releases a small amount of energy, which is dissipated as heat.
• Oxygen-free(anaerobic respiration or glycolysis) - multi-stage breakdown of glucose without the participation of oxygen. It's called fermentation. In muscles, as a result of anaerobic respiration, a glucose molecule breaks down into two molecules of lyruvic acid (C 3 H 4 O 3), which are then reduced to lactic acid (C 3 H 6 O 3). Phosphoric acid and ADP are involved in the breakdown of glucose.

  The overall equation for this stage: C 6 H 12 O 6 + 2H 3 PO 4 + 2ADP -> 2C 3 H 6 O 3 + 2ATP + 2H 2 O

  In yeast fungi, a glucose molecule without the participation of oxygen is converted into ethyl alcohol and carbon dioxide (alcoholic fermentation). In other microorganisms, glycolysis can result in the formation of acetone, acetic acid, etc. The breakdown of one glucose molecule produces two ATP molecules, in the bonds of which 40% of the energy is stored, the rest of the energy is dissipated in the form of heat.

• Oxygen breathing- the stage of aerobic respiration or oxygen cleavage, which takes place on the folds of the inner membrane of mitochondria - cristae. At this stage, the substances of the previous stage are broken down into the final decomposition products - water and carbon dioxide. As a result of the breakdown of two molecules of lactic acid, 36 molecules of ATP are formed. The main condition for the normal course of oxygen breakdown is the integrity of mitochondrial membranes. Oxygen respiration is the main step in providing cells with oxygen. It is 20 times more efficient than the oxygen-free stage.

  The overall equation for oxygen splitting is: 2C 3 H 6 0 3 + 60 2 + 36H 3 PO 4 + 36ADP -> 6CO 2 + 38H 2 O + 36ATP

According to the method of obtaining energy, all organisms are divided into two groups - autotrophic and heterotrophic.

Energy metabolism in aerobic cells of plants, fungi and animals proceeds in the same way. This indicates their relationship. The number of mitochondria in tissue cells varies; it depends on the functional activity of the cells. For example, there are many mitochondria in muscle cells.

The breakdown of fats into glycerol and fatty acids is carried out by enzymes - lipases. Proteins are first broken down into oligopeptides and then into amino acids.

Enzymes (from the Latin “fermentum” - fermentation, leaven), enzymes, specific proteins that increase the rate of chemical reactions in the cells of all living organisms. By chemical nature - proteins that have optimal activity at a certain pH, the presence of the necessary coenzymes and cofactors and the absence of inhibitors. Enzymes are also called biocatalysts by analogy with catalysts in chemistry. Each type of enzyme catalyzes the transformation of certain substances (substrates), sometimes only a single substance in a single direction. Therefore, numerous biochemical reactions in cells are carried out by a huge number of different enzymes. They are divided into 6 classes: oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases. Many enzymes have been isolated from living cells and obtained in crystalline form (for the first time in 1926).

The role of enzymes in the body

Enzymes are involved in all metabolic processes and in the implementation of genetic information. Digestion and assimilation of nutrients, synthesis and breakdown of proteins, nucleic acids, fats, carbohydrates and other compounds in the cells and tissues of all organisms - all these processes are impossible without the participation of enzymes. Any manifestation of the functions of a living organism - breathing, muscle contraction, neuropsychic activity, reproduction, etc. - is ensured by the action of enzymes. The individual characteristics of cells that perform certain functions are largely determined by a unique set of enzymes, the production of which is genetically programmed. The absence of even one enzyme or any defect in it can lead to serious negative consequences for the body.

Catalytic properties of enzymes

Enzymes are the most active of all known catalysts. Most reactions in a cell proceed millions and billions of times faster than if they occurred in the absence of enzymes. Thus, one molecule of the catalase enzyme is capable of converting up to 10 thousand molecules of hydrogen peroxide, toxic to cells, formed during the oxidation of various compounds, into water and oxygen in a second. The catalytic properties of enzymes are due to their ability to significantly reduce the activation energy of reacting compounds, that is, in the presence of enzymes, less energy is required to “start” a given reaction.

History of enzyme discovery

Processes that occur with the participation of enzymes have been known to man since ancient times, because the preparation of bread, cheese, wine and vinegar is based on enzymatic processes. But only in 1833, for the first time, an active substance was isolated from germinating barley grains, which converted starch into sugar and was called diastase (now this enzyme is called amylase). At the end of the 19th century. It has been proven that the juice obtained by grinding yeast cells contains a complex mixture of enzymes that ensure the process of alcoholic fermentation. From that time on, intensive study of enzymes began - their structure and mechanism of action. Since the role of biocatalysis was revealed in the study of fermentation, it was with this process that two established ones were associated with the 19th century. the names are “enzyme” (translated from Greek “from yeast”) and “enzyme”. True, the last synonym is used only in Russian-language literature, although the scientific direction involved in the study of enzymes and processes with their participation is traditionally called enzymology. In the first half of the 20th century. It was established that, by chemical nature, enzymes are proteins, and in the second half of the century, the sequence of amino acid residues was already determined for many hundreds of enzymes, and the spatial structure was established. In 1969, the chemical synthesis of the enzyme ribonuclease was first carried out. Tremendous advances have been made in understanding the mechanism of action of enzymes.

Location of enzymes in the body

In a cell, some enzymes are located in the cytoplasm, but mostly enzymes are associated with certain cellular structures, where they exert their action. In the nucleus, for example, there are enzymes responsible for replication - the synthesis of DNA (DNA polymerase), and for its transcription - the formation of RNA (RNA polymerase). Mitochondria contain enzymes responsible for energy storage; lysosomes contain most of the hydrolytic enzymes involved in the breakdown of nucleic acids and proteins.

Enzyme action conditions

All reactions involving enzymes occur mainly in a neutral, slightly alkaline or slightly acidic environment. However, the maximum activity of each individual enzyme occurs at strictly defined pH values. For the action of most enzymes in warm-blooded animals, the most favorable temperature is 37-40oC. In plants, at temperatures below 0o C, the action of enzymes does not completely stop, although the vital activity of plants is sharply reduced. Enzymatic processes, as a rule, cannot occur at temperatures above 70o C, since enzymes, like any proteins, are subject to thermal denaturation (structural destruction).

Sizes of enzymes and their structure

The molecular weight of enzymes, like all other proteins, lies in the range of 10 thousand - 1 million (but may be more). They may consist of one or more polypeptide chains and may be represented by complex proteins. The latter, along with the protein component (apoenzyme), includes low-molecular compounds - coenzymes (cofactors, coenzymes), including metal ions, nucleotides, vitamins and their derivatives. Some enzymes are formed in the form of inactive precursors (proenzymes) and become active after certain changes in the structure of the molecule, for example, after the cleavage of a small fragment from it. These include the digestive enzymes trypsin and chymotrypsin, which are synthesized by pancreatic cells in the form of inactive precursors (trypsinogen and chymotrypsinogen) and become active in the small intestine as part of pancreatic juice. Many enzymes form so-called enzyme complexes. Such complexes, for example, are embedded in the membranes of cells or cellular organelles and are involved in the transport of substances.

The substance undergoing transformation (substrate) binds to a specific part of the enzyme, the active center, which is formed by side chains of amino acids, often located in sections of the polypeptide chain that are significantly distant from each other. For example, the active center of the chymotrypsin molecule is formed by histidine residues located in the polypeptide chain at position 57, serine at position 195 and aspartic acid at position 102 (in total there are 245 amino acids in the chymotrypsin molecule). Thus, the complex arrangement of the polypeptide chain in the protein molecule - enzyme provides the opportunity for several amino acid side chains to appear in a strictly defined place and at a certain distance from each other. Coenzymes are also part of the active center (the protein part and the non-protein component separately do not have enzymatic activity and acquire the properties of an enzyme only when combined together).

Processes involving enzymes

Most enzymes are characterized by high specificity (selectivity) of action, when the conversion of each reactant (substrate) into a reaction product is carried out by a special enzyme. In this case, the action of the enzyme can be strictly limited to one substrate. For example, the enzyme urease, which is involved in the breakdown of urea to ammonia and carbon dioxide, does not react to methylurea, which is similar in structure. Many enzymes act on several structurally related compounds or on one type of chemical bond (for example, the enzyme phosphatases that cleave the phosphodiester bond). The enzyme carries out its action through the formation of an enzyme-substrate complex, which then breaks down to form the products of the enzymatic reaction and release the enzyme. As a result of the formation of the enzyme-substrate complex, the substrate changes its configuration; in this case, the converted enzyme-chemical bond is weakened and the reaction proceeds with less initial energy expenditure and, therefore, at a much higher speed. The rate of an enzymatic reaction is measured by the amount of substrate converted per unit time or the amount of product formed. Many enzymatic reactions, depending on the concentration of the substrate and the reaction product in the medium, can proceed in both the forward and reverse directions (an excess of the substrate shifts the reaction towards the formation of the product, while with excessive accumulation of the latter, substrate synthesis will occur). This means that enzymatic reactions can be reversible. For example, carbonic anhydrase in the blood converts carbon dioxide coming from tissues into carbonic acid (H2CO3), and in the lungs, on the contrary, it catalyzes the conversion of carbonic acid into water and carbon dioxide, which is removed during exhalation. However, it should be remembered that enzymes, like other catalysts, cannot shift the thermodynamic equilibrium of a chemical reaction, but only significantly accelerate the achievement of this equilibrium.

Nomenclature of enzyme names

When naming an enzyme as a base, take the name of the substrate and add the suffix “aza”. This is how, in particular, proteinases appeared - enzymes that break down proteins (proteins), lipases (break down lipids or fats), etc. Some enzymes received special (trivial) names, for example, digestive enzymes - pepsin, chymotrypsin and trypsin.

Several thousand different metabolic reactions take place in the cells of the body and, therefore, there are the same number of enzymes. In order to bring such diversity into the system, an international agreement on the classification of enzymes was adopted. In accordance with this system, all enzymes, depending on the type of reactions they catalyze, were divided into six main classes, each of which includes a number of subclasses. In addition, each enzyme received a four-digit code number (cipher) and a name indicating the reaction that the enzyme catalyzes. Enzymes that catalyze the same reaction in organisms of different species can differ significantly in their protein structure, but in nomenclature they have a common name and one code number.

Diseases associated with impaired enzyme production

The absence or decrease in the activity of any enzyme (often excessive activity) in humans leads to the development of diseases (enzymopathies) or death of the body. Thus, an inherited disease of children - galactosemia (leads to mental retardation) - develops as a result of a violation of the synthesis of the enzyme responsible for converting galactose into easily digestible glucose. The cause of another hereditary disease - phenylketonuria, accompanied by a disorder of mental activity, is the loss of the ability of liver cells to synthesize the enzyme that catalyzes the conversion of the amino acid phenylalanine into tyrosine. Determination of the activity of many enzymes in blood, urine, cerebrospinal, seminal and other body fluids is used to diagnose a number of diseases. Using this blood serum analysis, it is possible to detect myocardial infarction, viral hepatitis, pancreatitis, nephritis and other diseases at an early stage.

Human use of enzymes

Since enzymes retain their properties outside the body, they are successfully used in various industries. For example, papaya proteolytic enzyme (from papaya juice) - in brewing, for softening meat; pepsin - in the production of “ready-made” cereals and as a medicinal product; trypsin - in the production of baby food products; rennin (rennet from the stomach of a calf) - in cheese making. Catalase is widely used in the food and rubber industries, and cellulases and pectidases that break down polysaccharides are used to clarify fruit juices. Enzymes are necessary in establishing the structure of proteins, nucleic acids and polysaccharides, in genetic engineering, etc. With the help of enzymes, drugs and complex chemical compounds are obtained.

The ability of some forms of ribonucleic acids (ribozymes) to catalyze individual reactions, that is, to act as enzymes, has been discovered. Perhaps, during the evolution of the organic world, ribozymes served as biocatalysts before the enzymatic function was transferred to proteins better suited to perform this task.

Catalyze individual reactions occurring in the body. The combination of these reactions is metabolism (metabolism). In the body and its individual cells, on the one hand, the process of decomposition of individual cell components (lipids, carbohydrates, proteins), and, on the other hand, the synthesis of new molecules of these compounds constantly occurs. The processes of transformation of complex biological molecules into simpler ones are called dissimilation. Lipids and carbohydrates in the body ultimately break down into carbon dioxide and carbon dioxide, water and ammonia or its derivatives. Dissimilation processes occur with the release of energy, which is why they are also called energy metabolism. The biosynthesis of new organic compounds is called assimilation, or plastic metabolism. As a result of plastic exchange, the cell is provided with building material. Assimilation processes occur with the absorption of energy that is formed during energy metabolism.

The processes of assimilation and dissimilation occur constantly and complement each other. The energy generated in dissimilation processes is used for the biosynthesis of new cell-specific compounds. Substances synthesized as a result of assimilation processes are used to build new cells and individual organelles and to replace old cell molecules. The process of metabolism is possible only because the cells of living beings consume matter and energy from outside.

Typically, the processes of assimilation and dissimilation occur at approximately the same speed. However, in some situations, assimilation processes predominate (for example, increased growth of the body at a young age, increase in body weight with abundant nutrition and insufficient physical activity) or dissimilation processes (decreased body weight during fasting).

Unlike inanimate nature, where only processes associated with a decrease in the orderliness of the system occur spontaneously, in a living organism orderliness increases (with development) or is maintained at a more or less constant level. This is possible because energy is constantly being generated in the body due to dissimilation processes. Part of the energy is dissipated in the form of heat, and the rest is used to support vital processes: biosynthetic processes, maintaining an unbalanced distribution of ion concentrations outside and inside the cell, muscle contraction, cell movement, etc.

Released during dissimilation processes, it can be stored in the form of chemical (macroergic) bond energy in the ATP molecule.

ATP (adenosine triphosphoric acid) is a mononucleotide consisting of the nitrogenous base adenine, the five-carbon sugar ribose and three phosphoric acid residues. When the ATP molecule is hydrolyzed, which occurs under the action of special enzymes called ATPases, an ADP (adenosine diphosphoric acid) molecule is formed, inorganic phosphate and a large amount of energy is released (up to 40 kJ). That is why the terminal bond between phosphoric acid residues in the ATP molecule is called high-energy. The hydrolysis of ATP to AMP (adenosine monophosphoric acid) and pyrophosphate is also accompanied by a significant release of energy, that is, the bond between the terminal and second phosphoric acid residue in the ATP molecule is also high-energy. The cell mainly uses the energy from the terminal phosphate bond of the ATP molecule.

ATP is a universal energy accumulator in living nature. The processes that occur with the release of energy are accompanied by the synthesis of ATP from ADP and inorganic phosphate. In turn, processes occurring with energy consumption are accompanied by the hydrolysis of ATP to ADP and inorganic phosphate. That is why most ATPases are capable of providing some kind of work: for example, the hydrolysis of ATP by the actomyosin complex leads to contraction of muscle fibers, (ion pumps) ensure the transport of ions across the membrane in the direction of a higher ion concentration.

Energy exchange

Energy metabolism is a set of mechanisms by which molecules of cellular “fuel” are destroyed, and the energy contained in them is converted into the energy of phosphate bonds of ATP. Energy metabolism occurs in three main stages. The first, or preparatory, stage occurs in the digestive tract of animals and in the cytoplasm of cells. As a result, large molecules of biopolymers decompose into their constituent monomers: proteins are converted into amino acids, nucleic acids into mononucleotides, and then into sugars, nitrogenous bases and phosphoric acid, carbohydrates into simple sugars, and lipids into glycerol and fatty acids. During this stage, a small amount of energy is released and dissipated as heat.

At the second stage of energy metabolism, an oxygen-free (anaerobic) multi-stage transformation of the compounds formed as a result of the first stage into even simpler substances occurs. The energy released in this case is partially stored in the form of the terminal phosphate bond of ATP, that is, in the process of anaerobic cleavage, ATP is formed from ADP. A typical example of anaerobic transformation of substrates is glycolysis, as a result of which, in the absence of oxygen, glucose is converted into lactic acid. The overall glycolysis reactions can be represented by the following equation:

C 6 H 12 O 6 + 2ADP + 2H 3 PO 4 → 2C 3 H 6 O 3 + 2 ATP + 2H 2 O

As a result of glycolysis, one molecule of glucose, which contains 6 carbons, is first converted into two molecules of three-carbon pyruvic acid (C 3 H 4 O 3). In some cases, for example in muscle cells, pyruvic acid is reduced to lactic acid. In this case, energy is released (about 200 kJ), part of which (about 80 kJ) is stored in the form of two ATP molecules. For glycolysis to occur, the presence of ADP and phosphoric acid is necessary, but these substances are constantly present in the cytoplasm of cells. Anaerobic breakdown of glucose is characteristic of microorganisms that can exist under anaerobic conditions. The process of glycolysis also occurs intensively in skeletal muscles, which are capable of functioning for a long time in the absence of oxygen. In the cells of plants and some yeasts, glycolysis can follow the path of alcoholic fermentation: in this case, the pyruvic acid formed as a result of glycolysis is converted into carbon dioxide and acetaldehyde, which is then reduced to ethyl alcohol.

Since they appeared on Earth at a time when it did not yet contain oxygen, anaerobic fermentation should be considered as a simpler form of a biological mechanism that provides energy from nutrients. In most bacteria, yeast, fungi, as well as in the cells of all higher plants and animals, anaerobic breakdown of glucose is an obligatory stage of “fuel” conversion, followed by the aerobic phase - respiration.

Or oxidation, is the final, third stage of energy metabolism. During this stage, pyruvic acid, formed as a result of glycolysis, is oxidized to carbon dioxide and water. This stage occurs with the participation of numerous enzymes located in mitochondria in plants and animals, and in bacteria on the cytoplasmic membrane, and molecular oxygen.

The amount of energy released during the complete oxidation of glucose to CO 2 and H 2 O is almost 15 times greater than that released when glucose is converted into lactic acid. Thus, the process of glycolysis releases a very small amount of energy that can potentially be extracted from glucose. This is explained by the fact that the product of glycolysis, lactic acid, is a compound almost as complex as glucose, and its carbon atoms have almost the same oxidation state as in glucose (the ratio between the number of carbon atoms in lactic acid is the same as and in glucose). The product of the final stage of energy metabolism, CO2, is a much simpler compound in which the carbon atom is completely oxidized. It is during the oxidation process that a significant amount of energy is released, most of which (about 40%) is stored in the form of ATP.

General diagram of breathing processes. Pyruvic acid formed during glycolysis penetrates into the mitochondria, where it undergoes oxidative decarboxylation, turning into acetic acid (acetate), or rather, into its active form:

C 3 H 4 O 3 → CO 2 + CH 3 COOH

Active forms of acetate can also be formed in the body during the breakdown of amino acids and fatty acids. These forms of acetate enter the final stage of oxidative catabolism, where they undergo catalytic cleavage with the release of CO 2 and hydrogen atoms:

CH 3 COOH + 2H 2 O 2CO 2 + 8H

The cyclic set of reactions that result in the conversion of the active form of acetate into carbon dioxide and hydrogen atoms is called the tricarboxylic acid cycle, or Krebs cycle. The main part of the hydrogen atoms formed as a result of the cleavage of acetate is transferred to the oxidizing agent NAD + (nicotinamide adenine dinucleotide), a compound that belongs to pyridine nucleotides and is used in metabolic processes as a carrier of hydrogen atoms.

The energy released during respiration can be stored in the form of ATP due to the sequential occurrence of redox reactions. Redox reactions are reactions in which electrons are transferred from an electron donor (reducing agent) to an electron acceptor (oxidizing agent). In some redox reactions, electron transfer is accomplished by the transfer of hydrogen atoms; thus, dehydrogenation and oxidation are equivalent processes. The term reduction equivalents is often used to refer to electrons or hydrogen atoms taking part in a redox process.

Oxidizing agents and reducing agents function as coupled redox couples. In metabolic reactions, such redox pairs are represented, in particular, by pyrimidine nucleotides, NAD and NADP (the latter compound is the phosphorylated form of NAD). These compounds are part of enzymes involved in redox reactions. In redox reactions occurring in living systems, the oxidized form of these compounds (denoted as NAD + and NADP +) is converted into a reduced form (denoted as NADH and NADPH). In this case, two reducing equivalents leave the substrate molecule participating in the oxidation-reduction process. They are represented by a hydride ion (H -, two electrons and a proton), which binds to the NAD + molecule. The proton (H+) released after binding the hydride ion passes into the environment:

NAD + + 2H → NADH + H +

The reduced NAD molecule (NADH) interacts with the initial component of the respiratory chain. The respiratory chain consists of proteins located sequentially in the mitochondrial membrane, which are carriers of reducing equivalents (hydrogen or electrons). A significant part of the transporters is represented by cytochromes - iron-containing proteins. During the transfer of electrons along the respiratory chain, the valence of iron in cytochromes changes reversibly: Fe(II) -> Fe(III). Electrons are sequentially transferred from one carrier to another, and ultimately to molecular oxygen. The last cytochrome in the chain reacts with molecular oxygen. The process of electron transfer along the respiratory chain, which is a set of redox reactions, is accompanied by the release of a significant amount of energy. Part of this energy is stored in the form of ATP, which is formed as a result of phosphorylation of ADP coupled with oxidation.

In eukaryotic cells, the process of respiration, associated with energy transformation, occurs in the inner membrane of mitochondria. The inner membrane of mitochondria forms numerous deep folds called cristae. In bacteria capable of respiration, this process occurs on the cytoplasmic membrane. The conversion of energy released when electrons move through the respiratory chain is possible only if the inner mitochondrial membrane is impermeable to ions. This is due to the fact that energy is stored in the form of a difference in the concentrations (gradient) of protons.

The process of transferring reducing equivalents through the respiratory chain is carried out in such a way that at some stages not only an electron, but also a proton moves from one component of the respiratory chain to another (that is, a hydrogen atom is transferred). The components of the respiratory chain are located in the mitochondrial membrane such that this proton binds to a transporter on the inside of the mitochondrial membrane. Hydrogen atoms (a total of electron and proton) cross the membrane, the proton is released from the outside of the membrane, and the electrons continue their path along the respiratory chain. At the final stage, molecular oxygen and protons, which are constantly present in water, interact with the electrons that have passed through the respiratory chain. As a result of this reaction, water molecules are formed:

O 2 + 4e - + 4H + → 2H 2 O

The movement of protons from the matrix into the intermembrane space of mitochondria, which is carried out due to the functioning of the respiratory chain, leads to the fact that the mitochondrial matrix is ​​alkalized and the intermembrane space is acidified. Thus, during the functioning of the respiratory chain, the inner side of the mitochondrial membrane is charged negatively, and the outer side is charged positively. The resulting difference in proton concentration on different sides of the mitochondrial membrane can be used to synthesize ATP from ADP and inorganic phosphate. Synthesis is carried out by a special enzyme built into the mitochondrial membrane and called ATP synthase.

The ATP synthase molecule is located in the mitochondrial membrane in such a way that it forms a channel across the membrane through which protons can move. A significant part of the ATP synthase molecule protrudes inside the matrix, which directly ensures the formation of ATP from ADP and inorganic phosphate. When the channel opens, protons move freely along it from the outside of the membrane to the inside, that is, from the intermembrane space, where the proton concentration is high, to the matrix, where it is lower. However, the channel opens when the potential difference across the membrane reaches a critical level (more than 100 mV). When protons pass through the channel, energy is released, which ensures the addition of inorganic phosphate to ADP with the formation of a high-energy bond.

Energy balance. With the complete oxidation of one glucose molecule as a result of glycolysis and subsequent aerobic oxidation, thirty-eight molecules of ATP are synthesized. In total, this process can be represented as the following equation:

C 6 H 12 O 6 + 6O 2 + 38ADP + 38H 3 PO 4 -> 6CO 2 + 38ATP + 44H 2 O

Thus, as a result of the conversion of glucose into carbon dioxide and water, described by the equation:

C 6 H 12 O 6 + 6O 2 → 6СO 2 + 6H 2 O

ATP is synthesized from ADP and inorganic phosphate in accordance with the equation:

38ADP + 38H 3 PO 4 -> 38ATP + 38H 2 O

Considering that the terminal phosphate bond in the ATP molecule stores about 40 kJ of energy, we can conclude that the complete oxidation of glucose in the body allows us to store 1520 kJ of energy.

Plastic exchange

Plastic metabolism is a set of biosynthesis reactions, as a result of which substances characteristic of a given cell are formed from substances entering the cell. Plastic metabolism includes photosynthesis, the synthesis of proteins, nucleic acids, fats and carbohydrates.

Photosynthesis. Based on what type of nutrition living organisms use, they can be divided into two large groups: autotrophs and heterotrophs.

Heterotrophs are organisms that are not capable of synthesizing organic substances from inorganic ones. For this reason, they use ready-made organic compounds as food. Heterotrophs include animals, as well as a significant part of fungi and bacteria.

Autotrophs are organisms that synthesize organic compounds from inorganic ones. Autotrophs include all plants and some bacteria. In turn, autotrophs can be divided into chemo- and photosynthetic. Chemosynthetic bacteria include bacteria that are able to use the energy released during the oxidation of certain chemicals, such as hydrogen sulfide, ammonia, and nitrites. Photosynthetic organisms, which include both eukaryotes (higher green plants, green, brown and red algae, euglena and diatoms) and prokaryotes (blue-green algae, green and purple bacteria) use the energy of sunlight to synthesize organic compounds.

The synthesis of organic compounds using energy from sunlight is called photosynthesis.

The overall photosynthesis equation for all photosynthetic organisms, with the exception of bacteria, can be represented as follows:

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

Photosynthesis occurs in specialized organelles in green plants called chloroplasts. In photosynthetic bacteria, this process occurs on the outer membrane of the bacterium or in chromatophores, small spherical membrane vesicles located in the cytosol of the bacterial cell. Structurally, chloroplasts are close to mitochondria: they have a double membrane, with the inner membrane folded into many flattened vesicles called thylakoids. Inside the thylakoids are pigments that capture light. The process of photosynthesis can be divided into two phases: light and dark.

Light phase. Photosynthesis begins when the chloroplast is illuminated by visible light and includes reactions directly related to the use of light. All photosynthetic cells contain one or more classes of green pigments containing magnesium called chlorophylls. Chlorophyll molecules are capable of capturing light in the red region of the spectrum. The absorption of a quantum of light by a chlorophyll molecule leads to its “excitation,” that is, to the transition of one of the electrons to a higher energy level. The excited electron is transferred to the next component of the electron transport chain, similar to the respiratory chain. A significant part of the components of this chain are represented by cytochromes (iron-containing proteins) and copper-containing proteins. The process of electron transfer itself is a sequential redox reaction.

After an electron leaves the chlorophyll molecule to the next component of the electron transport chain (chlorophyll is oxidized), it is restored due to the electrons that are part of the water molecule. In this case, with the participation of special enzymes, the water molecule breaks down into an electron transferred to the oxidized chlorophyll molecule, a proton and atomic oxygen. This process occurs on the inside of the thylakoid membrane. Two oxygen atoms combine to form an O 2 molecule, which leaves the chloroplast by diffusion. Thus, oxygen, which is a product of photosynthesis, is formed from water.

As in the respiratory chain, at some stages of the transport chain in chloroplasts, electrons are transferred across the membrane together with protons (that is, in the form of hydrogen atoms), and then the paths of protons and electrons are separated: protons are transferred from one side of the membrane to the other, and electrons continue further along the transport chain. The final result of this process is the creation of a proton gradient: in this case, the internal space of the thylakoid is acidified and the inward-facing part of the membrane becomes positively charged, and the part of the membrane facing the intermembrane space becomes negatively charged (the intermembrane space becomes alkalized). The energy stored as a proton concentration gradient is used by ATP synthase to synthesize ATP from ADP and inorganic phosphate.

Ultimately, the electrons carried along the photosynthetic electron transport chain are incorporated into the oxidized form of nicotinamide adenine dinucleotide phosphate, NADP + , reducing the latter to NADPH. We have already mentioned that NAD + /NADH and NADP + /NADPH pairs are unified redox pairs of compounds used in various biochemical reactions as oxidizing or reducing agents.

Thus, as a result of the light stage of photosynthesis, electrons transferred from the excited chlorophyll molecule along the electron transport chain ensure, on the one hand, the creation of a proton gradient, the energy of which is stored in the form of the terminal phosphate bond of ATP, and on the other hand, ensure the formation of the reducing agent NAPH, which is then used in the dark phase of photosynthesis to form carbohydrates from carbon dioxide and water.

Dark phase of photosynthesis. Energy in the form of ATP and reducing equivalents in the form of NAPH, formed in photosynthetic organisms in the light, are subsequently used for the synthesis of carbohydrates, that is, for the reduction of CO 2 to glucose and other sugars. These reactions can occur both in light and in darkness, and are therefore called the dark phase of photosynthesis. The overall equation describing the dark process of glucose formation from CO 2 is as follows:

6CO 2 + 12NADPH + 18ATP + 12H 2 O -> C 6 H 12 O 6 + 12NADP + + 18 ADP + 18H 3 PO 4

The process of glucose synthesis is carried out as a result of a large number of sequential enzymatic reactions. Subsequently, more complex di- and polysaccharides, as well as amino acids, fatty acids and other organic compounds, can be formed from glucose.

The meaning of photosynthesis. The process of photosynthesis is the main process through which organic compounds are synthesized from inorganic compounds (carbon dioxide and water). Thus, photosynthetic organisms (autotrophs) are able, using the energy of the Sun, to synthesize organic substances necessary for their growth and development. Moreover, photosynthetic organisms themselves or their metabolic products serve as food for all other members of the biosphere (heterotrophs). Thus, life on Earth would have to cease without a constant supply of energy in the form of solar radiation and photosynthesis, which uses this energy.

In order to expend stored energy, organisms perform nutrient degradation, mainly oxidative degradation. Oxygen is used to carry out oxidative processes, and organic compounds are converted into oxygen dioxide. Photosynthesis helps maintain balance in the biosphere by reducing CO 2 to organic compounds and releasing molecular oxygen into the atmosphere. Only as a result of the emergence of organisms capable of producing oxygen could an environment emerge suitable for the development of all those forms of life that use oxygen.

Chemosynthesis. All autotrophic organisms are divided into two groups. One of them, called phototrophs, uses light as energy. These include all photosynthetic organisms. In addition, there are organisms that use the energy of redox reactions as an energy source for the synthesis of organic compounds. These organisms are called chemotrophic, and the process of synthesizing organic compounds using the energy of chemical reactions is called chemosynthesis. Chemotrophs include some bacteria that use the energy generated by the oxidation of ammonia to nitric acid, nitrous acid to nitric acid (nitrifying bacteria), as well as hydrogen sulfide to sulfuric acid (sulfur bacteria) and ferrous iron to ferric (iron bacteria).

Ways to increase the productivity of agricultural plants. One of the most important challenges facing a rapidly growing humanity is increasing the productivity of plants used as food. This task is primarily related to increasing the productivity of photosynthesis. For photosynthesis to proceed effectively, certain conditions must be met, namely:

Ensuring optimal intensity and duration of plant lighting, which is largely determined by the density of crops and the location of rows of plants in relation to the position of the Sun in the sky. When growing plants in greenhouses, the duration of daylight hours can be increased by illuminating the plants at night with special (phyto) lamps that provide light with sufficient intensity in the red region of the spectrum;

Maintaining optimal temperature conditions (for greenhouses the optimal temperature is 20-25°);

Ensuring optimal watering regime;

Sufficient content of mineral components in the soil (applying fertilizers to the soil);

Ensuring normal levels of carbon dioxide in the air of greenhouses, since a decrease in its concentration inhibits photosynthesis, and an increase inhibits plant respiration;

Timely and effective control of plant diseases.

However, the most promising at present are fundamentally new approaches, which consist in creating, using genetic engineering methods, new plant varieties characterized by high productivity and resistance to both diseases and various unfavorable conditions.

Protein biosynthesis

Proteins are the most important components of living things, not so much because they make up the largest part of the cell by mass, but because they ensure its functional activity and uniqueness. Almost all chemical processes occurring in the cell are carried out by enzyme proteins. Each cell has a set of specific proteins that are characteristic of that particular cell. It differs both from the set characteristic of the cells of another organism, and from the set characteristic of the cells of another given organism, since in each cell the synthesis of proteins specific to it is carried out. information about which proteins should be synthesized in the cells of a given organism is stored in the nucleus, it is written as a sequence of nucleotides in DNA. The part of a DNA molecule whose nucleotide sequence determines the sequence of amino acids in a particular protein is called a gene. A DNA molecule, depending on the evolutionary path that a given organism has gone through, can contain from hundreds to tens of thousands of genes.

DNA code. How can the sequence of nucleotides determine the sequence of amino acids? It is known that DNA consists of four types of nucleotides, that is, information in DNA is written in four letters (A, G, T, C). From mathematical calculations, it follows that more than one nucleotide is required to encode one amino acid, since 20 different amino acids are found in proteins. Since from 4 nucleotides only 16 different combinations of two nucleotides can be made (4 2 = 16), which is less than 20, then the “word” encoding a specific amino acid must consist of more than two letters. If we write the encoding “word” as a combination of three letters (nucleotides), then the number of different options will be 4 3 = 64. Thus, a combination of three nucleotides (triplet code) will be enough to encode 20 amino acids (64 > 20).

Combinations of three nucleotides that code for specific amino acids are called the DNA code, or genetic code. Currently, the DNA code has been completely deciphered, that is, it is known which specific triplet combinations of nucleotides encode the 20 amino acids that make up the protein. Using a combination of three nucleotides, it is possible to make a significantly larger number of coding “words” than is necessary to encode 20 amino acids. It turned out that each amino acid can be encoded by more than one triplet, that is, the genetic code is degenerate. For example, the amino acid phenylalanine can be encoded by both the sequence VUU and the sequence UUC. Only two amino acids (tryptophan and methionine) are encoded by one triplet. It should be noted that the term "degenerate" does not mean "imprecise", since one triplet cannot encode two amino acids.

An essential feature of the genetic code is that it contains no signals that separate one coding “word” (called a codon) from another. That is why reading information must begin from the correct place in the DNA (RNA) molecule and continue sequentially from one codon to another. Otherwise, the nucleotide sequence will be changed in all codons. This is confirmed by the detection of mutations in which one or two nucleotides are either dropped from the sequence (deletion) or inserted into it (insertion). With these mutations, a defective protein is synthesized as a result of a frameshift. In the event that three nucleotides are deleted or inserted, a protein is synthesized that differs from normal in that it is missing one amino acid (in the case of deletion of three nucleotides) or an additional amino acid appears (in the case of insertion of three nucleotides).

Another feature of the genetic code is that the three triplets (UAA, UAG and UGA) do not encode amino acids, but rather “punctuation marks”. They are stop signals that signal the end of the synthesis of the polypeptide chain.

The genetic code is universal, that is, the triplets encoding the same amino acid are the same in all living beings: the same codon encodes a specific amino acid in both a person and a virus or plant. Thus, the genetic language is the same for all species. The universality of the genetic code indicates that it arose in the process of genetic evolution almost in the form in which it exists today. The degeneracy of the code affects only the third base of the codon: for example, serine is encoded by the triplets UCA, UCC, UCA and UCG. Thus, the coding of a particular amino acid is determined mainly by the first two letters. One might think that the genetic code was first a doublet and contained information about 16 (or less) amino acids.

Transcription. Protein synthesis is carried out on ribosomes located in the cytoplasm of the cell. At the same time, information about the sequence of amino acids in a protein is stored in DNA. It turned out that during or before the start of the synthesis of a certain protein, the so-called matrix, or messenger RNA, is formed in the nucleus, which is an intermediary that transfers information from DNA to ribosomes. A messenger RNA (mRNA) molecule is synthesized using a specific section of DNA (gene) as a template. The mRNA molecule then leaves the nucleus and moves into the cytoplasm. By binding to ribosomes, it, in turn, serves as a matrix on which protein synthesis occurs.

mRNA synthesis occurs in the nucleus using an enzyme called DNA-dependent RNA polymerase. The newly synthesized mRNA has a nucleotide composition complementary to the nucleotide composition of the used DNA, with the only difference being that the adenine residues in the DNA template correspond to uracil residues in the synthesized mRNA. Thus, the information contained in the gene is transcribed into mRNA during the synthesis of mRNA. This process is called transcription (rewriting).

The transcription process, together with the DNA self-duplication reaction, which is called replication, is classified as a template synthesis reaction. Template synthesis reactions are reactions that occur using a matrix. The matrix (from the Latin matrix - uterus) is a ready-made structure, in accordance with which the synthesis of a new structure is carried out. During DNA synthesis (replication) and mRNA synthesis, one of the DNA strands is used as a template, on which a chain complementary to it is formed. Thus, as a result of matrix synthesis reactions, structures are formed that are built according to a strictly defined plan. Matrix synthesis reactions are characteristic only of living nature; as a result of their implementation, it becomes possible to transfer information from one generation of living beings to another (replication), as well as the synthesis of protein molecules, in accordance with the information embedded in the genetic material. For the synthesis of protein molecules, it is necessary to carry out two types of matrix synthesis reactions: transcription, which is necessary for the transfer of genetic information from the nucleus to the nucleus. cytoplasm, and translation.

Broadcast. The term translation (translation) in biology refers to reactions that result in the synthesis of a polypeptide chain in ribosomes using messenger RNA as a template. The polypeptide chain is lengthened during synthesis by sequential addition of individual amino acid residues, starting with the N-terminal residue. In order to understand how the formation of peptide bonds between the corresponding amino acids occurs, it is necessary to consider the structure of ribosomes and transfer RNAs (tRNAs) involved in the translation process.

Eukaryotic ribosomes have a diameter of about 220 A and a molecular weight of about 4 million daltons. Ribosomes in prokaryotes are smaller. Each ribosome consists of two unequal subunits, and the subunits can be separated from each other. Each subunit contains ribosomal RNA and protein. Some ribosomal proteins perform catalytic functions, that is, they are enzymes.

Transfer RNA. Transfer RNA molecules are small, their molecular weight is 23,000 - 30,000 daltons. The function of tRNA is to transfer certain amino acids to ribosomes during the synthesis of the polypeptide chain, with each amino acid being transferred by corresponding transport tRNAs. All tRNA molecules are capable of forming a characteristic conformation - the cloverleaf conformation. This conformation of the tRNA molecule occurs because its structure contains a significant number of nucleotides (4-7 in one section) complementary to each other. Intramolecular pairing of such nucleotides due to the formation of hydrogen bonds between complementary bases leads to the formation of such a structure. At the top of the clover leaf there is a triplet of nucleotides that is complementary to the corresponding mRNA codon. This triplet is different for tRNAs carrying different amino acids, and encodes exactly the amino acid that is carried by this tRNA. It's called an anticodon.

At the base of the clover leaf there is a site where the amino acid binds. The binding of an amino acid to tRNA is carried out due to the formation of a bond between the carboxyl group of the amino acid and the OH group of the adenylic acid residue, located at the terminal part of all tRNA molecules. Thus, a tRNA molecule not only carries a specific amino acid, it has in its structure a record that it carries this particular amino acid, and this record is made in the language of the genetic code.

Protein synthesis. Ribosomes are capable of binding mRNA, which carries information about the amino acid sequence of the protein being synthesized, transport RNA, which carries amino acids, and, finally, the synthesized polypeptide chain. The smaller subunit of the ribosome binds the mRNA and tRNA carrying the first (N-terminal) amino acid of the polypeptide chain, after which the large subunit binds to form a functioning (working) ribosome.

As the polypeptide chain is assembled, the ribosome moves along the filamentous tRNA molecule. At the same time, one mRNA molecule can contain several ribosomes, each of which synthesizes the polypeptide chain encoded by this tRNA. The further along the mRNA chain the ribosome moves, the longer the fragment of the protein molecule will be synthesized. When the ribosome reaches the end of the mRNA molecule, protein synthesis ends, and the ribosome with the newly synthesized protein leaves the mRNA molecule. The signal about the end of the synthesis of the polypeptide chain is given by three special codons, one of which is present in the terminal part of the mRNA molecule. Reading information from a tRNA molecule is possible only in one direction.

Even during the synthesis process, the newly formed end of the polypeptide chain can bind to special chaperone proteins that ensure its correct folding, and then is sent to the Golgi apparatus, from where the protein is transported to the place where it will work. The ribosome, which is freed from mRNA and the synthesized polypeptide chain, dissociates into subunits, after which the larger subunit, having contacted any mRNA, can bind a smaller subunit and form an active ribosome that can begin the synthesis of a new (or the same) protein.

The active center of the ribosome, in which the formation of a peptide bond between two neighboring amino acids occurs, is designed in such a way that it can simultaneously contain two adjacent codons (triplet) of mRNA. At the first stage, tRNA binds to messenger RNA due to codon-anticodon interaction. Since the anticodon located on tRNA and the codon located on mRNA are complementary, hydrogen bonds are formed between their constituent nitrogenous bases. At the second stage, binding to the neighboring codon of the second tRNA molecule is carried out in a similar way. In this case, tRNA molecules are oriented in the active center of the ribosome in such a way that the C=0 group of the first amino acid residue associated with the first tRNA is close to the free amino group of the amino acid residue included in the second transport tRNA. Thus, due to the codon-anticodon interaction between sequentially located mRNA codons and the corresponding tRNA anticodons, exactly those amino acids that are sequentially encoded in mRNA are located nearby.

At the next stage, as a result of the interaction of the free amino group, which is part of the amino acid residue of the newly arrived tRNA, with the esterified carboxyl group of the C-terminal amino acid residue of the first amino acid, a peptide bond is formed. The reaction is carried out by substitution, with the leaving group being the first tRNA molecule. As a result of this substitution, the elongated tRNA, already carrying a dipeptide, becomes associated with the ribosome. Catalysis of this reaction requires an enzyme called peptidyl transferase, which is part of the larger subunit of the ribosome.

In the final step, the tRNA-bound peptide moves from the site where the amino acid binds to the site where the resulting peptide binds. This movement process results from a change in the conformation of the ribosome. Simultaneously with the movement of the synthesized peptide chain, the ribosome moves along the mRNA, and the next codon of the mRNA appears in the active center of the ribosome, after which the events described above are repeated.

Protein synthesis occurs at a very high speed: a peptide consisting of 100 amino acids is synthesized in approximately 1 minute.

We have already mentioned that all synthesis processes, as a result of which more complex ones are formed from simpler molecules, are carried out with the expenditure of energy. Protein biosynthesis is a chain of reactions that require energy. Thus, the binding of one amino acid to tRNA requires the energy of two high-energy phosphate bonds. In addition, the formation of one peptide bond uses the energy of another high-energy phosphate bond. Thus, the formation of one peptide bond in a protein molecule requires the same amount of energy that is stored in three high-energy bonds of the ATP molecule.

Lecture: Metabolism and energy conversion - properties of living organisms

Metabolism

Metabolism (metabolism) These are the chemical processes that are life.

The basic basis of the life process is the synthesis of one’s own substances from the breakdown products obtained. Two varieties are being considered metabolic processes:

plastic exchange – anabolism or synthesis, in which potential energy is accumulated in the form of chemical bonds.

energy metabolism – catabolism, which is the decomposition of substances with the release of energy when bonds are broken.

Both groups are interconnected. Synthesis requires energy, which the body obtains through catalysis (cleavage).

Producing energy through catalysis

Life is possible through the use of chemical and light energy. Autotrophic plants synthesize glucose from water and carbon dioxide with the help of sunlight. Many bacteria live through chemosynthesis - the process of oxidation of inorganic substances using sulfur, nitrogen, and carbon compounds. Fungi and animals obtain energy and matter for synthesis by consuming sugars and other organic compounds created by plants. Some organisms can have mixed types of nutrition and be mixotrophs - euglena, sundew.

The role of enzymes is very important - they accelerate chemical reactions to the speeds necessary to maintain life, hundreds of thousands of times. Without them, life is impossible due to the low rates of chemical reactions. Enzymes have a protein structure, each is a catalyst for one type of reaction. The properties of enzymes are determined by their structure - the enzyme protein molecule contains an active center that interacts with target chemicals.

The level of enzyme activity is determined by various parameters:

Temperature. As it grows, activity increases.

The acidity of the environment. For most enzymes to work, a neutral environment is required, an acidic environment is preferable for mammalian digestion, and an alkaline environment is preferable for pancreatic secretion enzymes.

The amount of substrate.

The names of enzyme proteins end in -aza.

A feature of energy metabolism characteristic of aerobic organisms is its gradual passage. There are three stages:

Preparatory. This is digestion that occurs in the digestive vacuoles of lysosomes in protozoa and in the gastrointestinal tract in multicellular organisms. Functionally, it is the process of decomposition of macromolecules into monomers.

Glycolysis. Occurs in the cytoplasm. This is the oxygen-free transformation of glucose with its oxidation. Several cascading chemical reactions occur. As a result, 2 molecules of pyruvic acid (pyruvate) and 2 molecules of ATP are obtained from glucose. Partially released energy during reactions is stored back in ATP, and part of it is dissipated into space in the form of heat.

Oxygen stage. This is a cascade two-step process: the Krebs cycle followed by oxidative phosphorylation (respiration). Pyruvate at this stage is converted to carbon dioxide and water, producing 34 molecules of ATP, and then producing 2 more during respiration. From a chemical point of view, energy metabolism looks like: C6H12O6 + 6O2 = 6CO2 + 6H2O + 38ATP.

Other types of energy production

Fermentation. One of the main ways of obtaining energy by the simplest and some cells of higher animals. At the same time, pyruvate obtained from glucose by plant cells is included in alcoholic fermentation, breaking down into carbon dioxide and alcohol. In animals, pyruvate undergoes lactic acid fermentation - it turns into lactic acid. In conditions of lack of oxygen, muscle cells resort to a less efficient but faster method of ATP synthesis. Excess lactic acid, which does not have time to be metabolized due to lack of oxygen, causes muscle pain. There are also types of fermentation such as methane (a method of wastewater treatment), butyric acid, and acetic acid.

Photosynthesis. It was proven in 1630 by the Dutchman van Helmont, who discovered the independent creation of nutrients by plants. The change in air composition by plants was proven in 1771 by D. Priestley. Now science considers photosynthesis as the process of synthesis by green plant cells of glucose from water and carbon dioxide under the influence of sunlight.

Chlorophyll is a complex molecule consisting of approximately a dozen aromatic five-membered rings with magnesium complexes.

The sufficiently studied light phase of photosynthesis is divided into several stages:

a photon received from the outside causes the chlorophyll molecule to be excited, its electrons shift to a higher level;
electrons are picked up by ionized nicotinamide diphosphate, which leads to its reduction;

Photolysis of water occurs - with decomposition into ionized hydrogen, 4 electrons, and an oxygen molecule.

This primary phase occurs on the folded formations of the inner membrane layer - the thylakoids of the chloroplasts. Stacks of membranes inside the plastid are called grana.

During the dark photosynthetic phase, carbohydrate molecules are synthesized between grana inside the chloroplast (in the stroma), using the energy of ATP nicotiamide diphosphate, as well as carbon dioxide.

Chemosynthesis. In conditions of lack of nutrients and sunlight, many types of chemosynthetic bacteria live:

iron bacteria - obtain energy by increasing the oxidation state of iron - from divalent to trivalent.

hydrogen - convert molecular hydrogen into water.

thionic - live due to the oxidation of thiosulfates and other sulfur compounds, as well as its molecular form to sulfuric acid. Many of them can live in extremely acidic environments and are indifferent to high concentrations of heavy metals, leaching them from ores.

sulfur bacteria - convert hydrogen sulfide into pure sulfur and sulfuric acid salts;
nitrifying - convert ammonia into nitric and nitrous acids.

Chemosynthetics are an important link in the cycle of substances.