Physiological role and structure of proteins. Function of proteins in the body. Reserve, or trophic

Fats

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The physiological role of proteins consumed with food is that they are the main element of the body's plastic metabolism, being a source of "building material". Proteins received from food are broken down to their structural elements - amino acids. Foods containing proteins cannot be replaced by foods containing fats and carbohydrates Some of the amino acids that make up protein molecules can be synthesized in the body. These are the so-called nonessential amino acids... The other part ( essential amino acids) cannot be synthesized, therefore it must be taken with food. The main sources of proteins for humans are: meat, eggs, fish, beans, peas, beans.

Unlike carbohydrates and fats, the body does not accumulate and store proteins. If more of them are supplied with food than is necessary to meet current needs, the products of hydrolysis (amino acids) undergo biochemical changes and are included in metabolic reactions. A part of amino acids, not used as structural elements and energetic material, is deaminated. The remaining carbon sequences are transformed and included in the reactions of carbohydrate metabolism. The split-off nitrogen is excreted from the body in the urine in the form of urea.

Fats are an important part of the diet. They are part of many food products: meat, fish, milk. And products such as lard, butter, are almost entirely composed of fats. Typically, vegetable fats differ from animal fats in that they contain more unsaturated fatty acids.

During hydrolysis in the body, fats (glycerides) are broken down into glycerol and fatty acids, some of which are irreplaceable, since they cannot be synthesized in the human body (for example, some unsaturated acids - linoleic, linolenic).

Like other nutrients, fats take part in plastic and energy exchange. Their oxidation leads to the release of much more energy than the oxidation of proteins and carbohydrates. In addition, fats can accumulate in the body, forming a universal depot of energetically valuable material. Excessive carbohydrates and part of the proteins entering the body can be transformed into fat, which leads to the growth of its deposits. If necessary, the fat stored in this way can be converted into glycogen and used in carbohydrate metabolism reactions.

Plant food - fruits, vegetables, cereals - is the main source of carbohydrates for humans, the main of which is polysaccharide starch.

Carbohydrates - main source of energy in the body, since their breakdown is more accessible than the breakdown of lipids, although the breakdown of carbohydrates leads to the release of fewer calories than the degradation of the same amounts of fat. Carbohydrates can be stored in small quantities in liver and muscles as glycogen. The products of the breakdown of proteins and fats (amino acids and fatty acids), being transformed, are able to be included in carbohydrate metabolism.

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Lecture number 3

Topic: Physiological significance of proteins and amino acids in human nutrition.

1 The most important groups of peptides and their physiological role.

2 Characteristics of proteins of food raw materials.

3 New forms of protein foods.

4 Functional properties of proteins.

1 The most important groups of peptides and their physiological role.

Peptides are oligomers composed of amino acid residues. They have a low molecular weight (the content of amino acid residues ranges from several pieces to several hundred).

In the body, peptides are formed either during synthesis from amino acids, or during hydrolysis (cleavage) of protein molecules.

Today, the physiological significance and functional role of the most common groups of peptides have been established, on which human health, organoleptic and sanitary-hygienic properties of food products depend.

Buffer peptides. In the muscles of animals and humans, dipeptides have been found that perform buffer functions, that is, maintain a constant pH level.

Hormone peptides... Hormones - substances of organic nature, produced by the cells of the glands, regulate the activity of individual organs, glands and the body as a whole: reduction of smooth muscles of the body and milk secretion by the mammary glands, regulation of the activity of the thyroid gland, activity of the growth of the body, the formation of pigments that determine the color of eyes, skin, hair ...

Neuropeptides. These are two groups of peptides ( endorphins and enkephalins ) contained in the brain of humans and animals. They determine the reactions of behavior (fear, fear), affect the processes of memorization, learning, regulate sleep, relieve pain.

Vasoactive peptides synthesized from food proteins as a result, they have an effect on vascular tone.

Peptide toxins are a group of toxins produced by world organisms, poisonous mushrooms, bees, snakes, sea molluscs and scorpions. They are undesirable for the food industry. The greatest danger is posed by toxins of microorganisms (Staphylococcus aureus, botulism bacteria, salmonella), including fungi that develop in raw materials, semi-finished products and finished food products.

Antibiotic peptides... Representatives of this group of peptides of bacterial or fungal origin are used in the fight against infectious diseases caused by streptococci, pneumococci, staphylococci and other microorganisms.

Flavor peptides- first of all, these are compounds with a sweet or bitter taste. Bitter peptides are formed in young, unripe, enzymatic cheeses. Sweet peptides ( aspartame ) are used as a sugar substitute.

Protective peptides perform protective functions, primarily antioxidant.

2 Characteristics of proteins of food raw materials.

Peptides with a molecular weight of more than 5000 Da and performing a particular biological function are called proteins.

The functional properties of proteins depend on the sequence of amino acids in the polypeptide chain (the so-called primary structure), as well as on the spatial structure of the polypeptide chain (depending on the secondary, tertiary and quaternary structures).

Different food products are distinguished by their qualitative and quantitative protein content.

In cereals the total protein content is 10–20%. Analyzing the amino acid composition of the total proteins of various cereals, it should be noted that all of them, with the exception of oats, are poor in lysine (2.2 ÷ 3.8%). Wheat, sorghum, barley and rye proteins are characterized by relatively small amounts of methionine and cysteine (1.6 ÷ 1.7 mg / 100 g protein). The most balanced in terms of amino acid composition are oats, rye and rice.

In legumes (soybeans, peas, beans, vetch) the total protein content is high and amounts to 20 ÷ 40%. Soybeans are most widely used. Its rate is close to one in five amino acids, but soy contains insufficient tryptophan, phenylalanine and tyrosine and is very low in methionine.

In oilseeds(sunflower, cotton, rapeseed, flax, castor oil, caryander) the total protein content is 14 ÷ 37%. At the same time, the amino acid rate of proteins of all oilseeds (to a lesser extent cotton) is high enough even for limiting acids. This fact determines the feasibility of obtaining concentrated forms of protein from oilseeds and the creation of new forms of protein food on their basis.

Relatively low content of nitrogenous substances in potatoes(about 2%), vegetables(1 ÷ 2%) and fruits(0.4 ÷ 1.0%) indicate an insignificant role of these types of edible plant materials in providing food with protein.

Meat, milk and the products obtained from them contain proteins necessary for the body, which are favorably balanced and well absorbed (while the balance and absorption rate of milk is higher than that of meat). The protein content in meat products ranges from 11 to 22%. The protein content in milk ranges from 2.9 to 3.5%.

3 New forms of protein foods.

Today, in a constantly growing society and limited resources, a person faces the need to create modern food products that have functional properties and meet the requirements of the science of healthy nutrition.

New forms of protein food are food products obtained on the basis of various protein fractions of food raw materials using scientifically proven processing methods, and having a certain chemical composition, structure and properties.

Various vegetable protein sources are widely recognized: legumes, grain and cereals and by-products of their processing, oilseeds; vegetables and melons, vegetative mass of plants.

At the same time, soy and wheat are mainly used for the production of protein products.

Products of processing of soy proteins are divided into three groups, differing in protein content: flour and cereals are obtained by grinding, they contain 40 ÷ 45% of protein from the total mass of the product; soy concentrates are obtained by removing water-soluble components; they contain 65 ÷ 70% protein; soy isolates are obtained by protein extraction and contain at least 90% protein.

Soy-based get textured protein foods, in which soy proteins are used, for example, instead of meat proteins. Hydrolyzed soy proteins are called modified... They are used as functional and flavoring food additives.

Today, soy-based also produces soy milk, soy sauce, tofu (bean curd) and other food products.

Dry wheat gluten with a protein content of 75 ÷ 80% is obtained from wheat or wheat flour by the method of water extraction.

At the same time, the presence of limiting amino acids in plant proteins determines their inferiority. The way out here is the joint use of different proteins, which provides a mutual enrichment effect. If, at the same time, an increase in the amino acid rate of each essential limiting amino acid is achieved in comparison with the individual use of the original proteins, then one speaks of simple enrichment effect, if after mixing the amino acid rate of each amino acid exceeds 1.0, then is true enrichment effect... The use of such balanced protein complexes provides an increase in the digestibility of plant proteins up to 80 ÷ 100%.

4 Functional properties of proteins.

Proteins and protein concentrates are widely used in food production due to their inherent unique functional properties, which are understood as physicochemical characteristics that determine the behavior of proteins during processing into food products and provide a certain structure, technological and consumer properties of the finished product.

The most important functional properties of proteins include solubility, water and fat binding capacity, the ability to stabilize dispersed systems (emulsions, foams, suspensions), and form gels.

Solubility- this is the primary indicator for assessing the functional properties of proteins, characterized by the amount of protein passing into the solution. Solubility is most dependent on the presence of non-covalent interactions: hydrophobic, electrostatic and hydrogen bonds. Proteins with high hydrophobicity interact well with lipids, with high hydrophilicity they interact well with water. Since proteins of the same type have the same charge, they repel, which contributes to their solubility. Accordingly, in the isoelectric state, when the total charge of the protein molecule is zero, and the degree of dissociation is minimal, the protein has a low solubility and can even coagulate.

Water binding the ability is characterized by the adsorption of water with the participation of hydrophilic amino acid residues, fat-binding- adsorption of fat due to hydrophobic residues. On average, 1 g of protein can bind and retain 2-4 g of water or fat on its surface.

Fat emulsifying and foaming the ability of proteins is widely used in the production of fat emulsions and foams, that is, heterogeneous systems water-oil, water-gas. Due to the presence of hydrophilic and hydrophobic zones in protein molecules, they interact not only with water, but also with oil and air and, acting as a shell at the interface between two media, contribute to their distribution in each other, that is, the creation of stable systems.

Gelling the properties of proteins are characterized by the ability of their colloidal solution from a free dispersed state to pass into a bound-dispersed state with the formation of systems with the properties of solids.

Visco-elastic-elastic the properties of proteins depend on their nature (globular or fibrillar), as well as the presence of functional groups that bind protein molecules to each other or to a solvent.

Proteins, fats, carbohydrates, vitamins are the main nutrients in the human diet. Nutrients are such chemical compounds or individual elements that the body needs for its biological development, for the normal course of all vital processes.

Proteins are high molecular weight nitrogenous compounds, the main and essential part of all organisms. Protein substances are involved in all vital processes. For example, metabolism is provided by enzymes that are protein-related in nature. Proteins are also contractile structures necessary for the fulfillment of the contractile function of muscles - actomyosin; supporting tissues of the body - collagen of bones, cartilage, tendons; integumentary tissues of the body - skin, nails, hair.

By their composition, proteins are divided into: simple - proteins (during hydrolysis only amino acids and ammonia are formed) and complex - proteids (during hydrolysis, non-protein substances are also formed - glucose, lipoids, dyes, etc.).

Of the many nutrients, proteins play the most important role. They serve as a source of essential amino acids and the so-called nonspecific nitrogen required for protein synthesis.

The level of protein supply largely determines the state of health, physical development, physical performance, and in young children - and mental development. The sufficiency of protein in the diet and its high quality make it possible to create optimal conditions for the internal environment of the body, which are necessary for growth, development, normal human activity and performance. Under the influence of protein deficiency, pathological conditions such as edema and obesity of the liver can develop; violation of the functional state of the organs of internal secretion, especially the gonads, adrenal glands and pituitary gland; violation of conditioned reflex activity and processes of internal inhibition; decreased immunity; alimentary dystrophy. Proteins are composed of carbon, oxygen, hydrogen, phosphorus, sulfur and nitrogen, which are part of amino acids - the main structural components of protein. Proteins differ in the level of amino acids and the sequence of their connection. Distinguish between animal and vegetable proteins.

Unlike fats and carbohydrates, proteins contain, in addition to carbon, hydrogen and oxygen, nitrogen - 16%. Therefore, they are called nitrogen-containing food substances. The animal body needs proteins in a ready-made form, since it cannot synthesize them, like plants, from the inorganic substances of the soil and air. Food substances of animal and plant origin serve as a source of protein for humans. Proteins are necessary primarily as a plastic material, this is their main function: they make up 45% of the solid remainder of the body.

Proteins are also part of hormones, erythrocytes, and some antibodies, with high reactivity.

In the process of vital activity, there is a constant aging and death of individual cellular structures, and food proteins serve as building materials for their restoration. Oxidation in the body of 1 g of protein gives 4.1 kcal of energy. This is its energetic function. Protein is of great importance for human higher nervous activity. The normal protein content in food improves the regulatory function of the cerebral cortex, increases the tone of the central nervous system.

With a lack of protein in the diet, a number of pathological changes occur: growth and development of the body slows down, weight decreases; the formation of hormones is disrupted; the reactivity and resistance of the body to infections and intoxications decrease. The nutritional value of food proteins depends primarily on their amino acid composition and the completeness of utilization in the body. There are 22 known amino acids, each with a special meaning. The absence or lack of any of them leads to disruption of certain body functions (growth, hematopoiesis, weight, protein synthesis, etc.). The following amino acids are especially valuable: lysine, histidine, tryptophan, phenylalanine, leucine, isoleucine, threonine, methionine, valine. For young children, histidine is essential.

Some amino acids cannot be synthesized in the body and replaced by others. They are called irreplaceable. Depending on the content of nonessential and irreplaceable amino acids, food proteins are divided into complete ones, the amino acid composition of which is close to the amino acid composition of the proteins of the human body and contains all essential amino acids in sufficient quantities, and into deficient ones, which lack one or more essential amino acids. The most complete proteins of animal origin, especially the proteins of the yolk of chicken eggs, meat and fish. Of plant proteins, soy proteins have a high biological value and, to a somewhat lesser extent, beans, potatoes and rice. Defective proteins are found in peas, bread, corn, and some other plant foods.

Physiological and hygienic standards for protein requirements. These norms are based on the minimum amount of protein that is able to maintain the nitrogen balance of the human body, i.e. the amount of nitrogen introduced into the body with food proteins is equal to the amount of nitrogen excreted from it in the urine per day.

The daily intake of dietary protein should fully ensure the nitrogen balance of the body with full satisfaction of the energy needs of the body, ensure the integrity of the body proteins, maintain the high performance of the body and its resistance to unfavorable environmental factors. Proteins, unlike fats and carbohydrates, are not stored in the body in reserve and must be introduced daily with food in sufficient quantities.

Physiological daily protein intake depends on age, gender and occupational activity. For example, for men it is 96-132 g, for women - 82-92 g. These are the norms for residents of large cities. For residents of small towns and villages engaged in heavier physical work, the daily protein intake increases by 6 g. The intensity of muscle activity does not affect nitrogen metabolism, but it is necessary to ensure sufficient development of the muscular system for such forms of physical work and maintain its high efficiency.

An adult in normal living conditions, with light work, requires an average of 1.3 -1.4 g of protein per 1 kg of body weight per day, and with physical work - 1.5 g or more (depending on the severity of work).

In the daily diet of athletes, the amount of protein should be 15-17%, or 1.6-2.2 g per 1 kg of body weight.

Proteins of animal origin in the daily diet of adults should occupy 40 - 50% of the total amount of consumed proteins, athletes - 50 - 60, children - 60 - 80%. Excessive consumption of proteins is harmful to the body, since the processes of digestion and the excretion of decay products (ammonia, urea) through the kidneys are hampered.

Of the many nutrients, proteins play the most important role. They serve as a source of essential amino acids and the so-called nonspecific nitrogen required for protein synthesis.

Proteins are also part of hormones, erythrocytes, and some antibodies, with high reactivity.

In the daily diet of athletes, the amount of protein should be 15-17%, or 1.6-2.2 g per 1 kg of body weight.

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Introduction

Section 1. Physiological role of protein

1.1 Structural function of proteins

1.2 Protein metabolism in the human body

1.3 Nitrogen equilibrium

Section 2. Protein metabolism in various conditions of the body

2.1 Protein metabolism during muscle activity

2.2 Disorder of amino acid metabolism

Introduction

Proteins are the most important component of nutrition. Proteins are the basis of the structural elements of cells and tissues. The main manifestations of life are associated with proteins: metabolism, muscle contractions, irritability of nerves, the ability to grow, reproduce, and think. By binding significant amounts of water, proteins form dense colloidal structures that determine the configuration of the body. In addition to structural proteins, protein substances include hemoglobin - the oxygen carrier in the blood, enzymes - the most important accelerators of biochemical reactions, some hormones, nucleoproteins - determining the direction of protein synthesis in the body, which are carriers of hereditary properties.

A complete protein consists of 20 amino acids, the combination of which in protein molecules can lead to their huge diversity. The only source of protein formation in the body is the amino acids of food proteins. The value of the supply of protein to the body is judged by the indicators of nitrogen balance.

Proteins are the only source of nitrogen assimilated by the body. Taking into account the amount of nitrogen supplied with food and released from the body, one can judge the well-being or violation of protein metabolism. In the body of healthy adults, a nitrogen balance is observed, this is when the amount of nitrogen supplied with food "equals the amount of nitrogen excreted from the body. In children, the nitrogen balance is characterized by the accumulation of proteins in the body. At the same time, the amount of nitrogen supplied with food significantly exceeds its excretion with decay products.In this case, a positive nitrogenous balance.A positive nitrogenous balance is observed in the body of a child, boy and girl.

In people who receive an insufficient amount of protein from food or in seriously ill people in whose body protein is poorly absorbed, there is a loss of nitrogen, that is, a negative nitrogen balance. For an adult, the minimum rate is 40-50 g of protein per day. If work is not associated with intense physical labor, the body of an adult on average needs about 1-1.2 g of protein per 1 kg of body weight with food. This means that a person weighing 70-75kg should get 70 to 90g of protein per day. With an increase in the intensity of physical labor, the body's needs for protein also increase.

The nutritional value of various types of proteins depends on their amino acid composition. Only 8 have a complete protein consisting of 20 amino acids, which are indispensable in the diet for an adult (and one more for a young child). - Essential amino acids are not synthesized in the body and must necessarily enter the body in certain quantities with food. In accordance with the concept of a balanced diet, the following values can be named, characterizing the minimum requirements for each of the essential amino acids for the adult body and their optimal ratios to ensure the use of protein.

If any of the amino acids in food proteins is less, then it will not be synthesized, but then other amino acids cannot be fully utilized by the body. The amino acid composition of egg proteins was taken as ideal, since their assimilation by the human body is close to 100%. The degree of assimilation of other products of animal origin is also very high: milk (75-80%), meat (70-75%), fish (70-80%), etc.

Many plant foods, especially cereals, contain proteins of reduced bioavailability. Most plant materials are deficient in sulfur-containing amino acids.

Section 1. Physiological role of protein

1.1 Structural function of protein

Proteins are complex organic compounds built from amino acids. The composition of protein molecules includes nitrogen, carbon, hydrogen and some other substances. Amino acids are characterized by the presence of an amino group (NH2) in them.

Proteins differ from each other in the content of different amino acids in them. In this regard, proteins have specificity, that is, they perform different functions. Proteins of animals of different species, different individuals of the same species, as well as proteins of different organs and tissues of one organism differ from each other. The specificity of proteins allows them to be introduced into the body only through the digestive organs, where they are broken down into amino acids and in this form are absorbed into the blood. In tissues, proteins that are characteristic of these tissues are formed from amino acids delivered by the blood. Proteins are the main material from which the cells of the body are built (Abramova T. 1994)

The functions of proteins are extremely diverse. Each given protein as a substance with a certain chemical structure performs one highly specialized function and only in some cases several, as a rule, interrelated functions. About one of the central functions, their participation in the overwhelming majority of chemical transformations as enzymes or the most important component of enzymes. Enzymes for the most part ensure the flow of processes necessary for life at low temperatures and pH close to neutral.

The largest functional group of proteins is enzymes. Each enzyme is specific to one degree or another, i.e. functionally adapted to a certain substrate, sometimes to a certain type of chemical bonds. Under the influence of various influences, the structure of the protein molecule can change, and therefore the activity of the enzyme also changes. For example, there is a dependence of the rate of an enzymatic reaction on changes in temperature and pH.

Some biological molecules are capable of accelerating or inhibiting (from the Latin inhibere - to restrain, to stop), that is, to suppress the activity of enzymes - this is one of the ways to regulate enzymatic reactions. (Komov V.P. 2004)

Proteins are chemical structures that represent a linear sequence of amino acids formed during a series of condensation reactions that involve the a-carboxyl and a-amine groups of adjacent amino acids. The bonds formed as a result of these reactions are called peptide bonds. Two amino acids form a dipeptide, and the longer chains form polypeptides. Each polypeptide chain has one amine and one carboxyl terminus, which can form subsequent peptide bonds with other amino acids. Many proteins are made up of more than one polypeptide chain, each of which forms a subunit. The order in which amino acids are arranged in a chain is determined during protein synthesis by a sequence of nucleotide bases in a specific DNA containing genetic information related to this protein. The amino acid sequence determines the final structure, since the side chains of the amino acid component attract, repel, or physically interfere with each other, which "forces" the molecule to fold and take the final, corresponding shape. The primary structure of a protein is a specific sequence of amino acids in the polypeptide chain, as well as their quantitative and qualitative composition. The sequence of amino acids in individual proteins is genetically fixed and determines the individual and species specificity of the protein. Deciphering the primary structure of a protein is of great practical importance, as it opens up the possibility of its synthesis in the laboratory. Thanks to the deciphering of the structure of the hormone insulin and immunoglobulin, these proteins are obtained synthetically and are widely used in medicine. The study of the primary structure of hemoglobin made it possible to reveal changes in its structure in humans with certain diseases. At present, the primary structure of more than 1000 proteins has been deciphered, including the enzymes ribonuclease, carboxypeptidase, myoglobin, cytchrome b, and many others.

The secondary structure of a protein is the spatial folding of the polypeptide chain. There are three types of secondary structure: a-helix, layered helix (or B-helix), and collagen helix.

When an a-helix is formed, the polypeptide chain is helical due to hydrogen bonds in such a way that the turns of the peptide chain are periodically repeated. This creates a compact and strong structure of the protein polypeptide chain.

The layered structure of the protein is a linear polypeptide chain located in parallel and tightly linked by hydrogen bonds. This structure is the basis for fibrillar proteins.

The collagen helix of the protein is distinguished by the more complex folding of the polypeptide chains. Individual chains are coiled and twisted around one another, forming a supercoil. This structure is typical for collagen. The collagen coil has high elasticity and strength of the steel thread. ("Fundamentals of Biochemistry" 1986)

Tertiary structure The general arrangement, the mutual folding of different regions, domains and individual amino acid residues of a single polypeptide chain is called the tertiary structure of a given protein. It is impossible to draw a clear boundary between the secondary and tertiary structures, however, the tertiary structure is understood as steric relationships between amino acid residues that are far apart from each other along the chain. Quaternary structure If proteins consist of two or more polypeptide chains linked by non-covalent (non-peptide and non-disulfide) bonds, then they are said to have a quaternary structure. Such aggregates are stabilized by hydrogen bonds and electrostatic interactions between residues on the surface of polypeptide chains. Such proteins are called oligomers, and their constituent individual polypeptide chains are protomers, monomers or subunits.

Many oligomeric proteins contain two or four protomers and are called dimers or tetramers, respectively. Oligomers containing more than four protomers are quite common, especially among regulatory proteins (for example, transcarbamoylase). Oligomeric proteins play a special role in intracellular regulation: their protomers can slightly change mutual orientation, which leads to a change in the properties of the oligomer.

The structural function of proteins or plastic, the function of proteins is that proteins are the main constituent of all cells and intercellular structures. Proteins are also found in the basic substance of cartilage, bones and skin. Protein biosynthesis determines the growth and development of the body.

The catalytic or enzymatic function of proteins is that proteins are able to accelerate biochemical reactions in the body. All currently known enzymes are proteins. The implementation of all types of metabolism in the body depends on the activity of enzyme proteins.

The protective function of proteins is manifested in the formation of immune bodies (antibodies) when a foreign protein (for example, bacteria) enters the body. In addition, proteins bind toxins and poisons that enter the body, and ensure blood clotting and stopping bleeding in case of injury.

The transport function of proteins is that proteins are involved in the transfer of many substances. So, the supply of cells with oxygen and the removal of carbon dioxide from the body is carried out by a complex protein - hemoglobin, lipoproteins provide the transport of fats, etc.

The transfer of hereditary properties in which nucleoproteins play a leading role is one of the most important functions of proteins. Nucleic acids are part of the nucleoproteins. There are two main types of nucleic acids: ribonucleic acids (RNA), which contain adenine, cytosine, uracil, ribose and phosphoric acid, and deoxyribonucleic acids (DNA), which contain deoxyribose instead of ribose and thymine instead of uracil. The most important biological function of nucleic acids is their participation in the biosynthesis of proteins. Nucleic acids are not only necessary for the process of protein biosynthesis itself, they also provide for the formation of proteins specific to a given species and organ.

The regulatory function of proteins is aimed at maintaining biological constants in the body, which is ensured by the regulatory effects of various hormones of a protein nature.

The energy role of proteins is to provide energy for all life processes in the body of animals and humans. Proteins-enzymes determine all aspects of metabolism and the formation of energy not only from proteins themselves, but also from carbohydrates and fats. When 1 g of protein is oxidized, an average of 16.7 kJ (4.0 kcal) energy is released.

The protein bodies of different people have individual specificity. This means that the formation of immune bodies in the human body during organ transplantation, as a result of which a reaction of rejection of the transplanted organ may occur.

Individual differences in protein composition are inherited. Violation of the genetic code in some cases can cause severe hereditary diseases (Kositsky G.I. 1985).

1.2 Protein metabolismin the human body

An important criterion for the nutritional value of proteins is the availability of amino acids. The amino acids of most animal proteins are completely released during digestion. The exception is the proteins of the supporting tissues (collagen and elastin). Proteins of plant origin are poorly digested in the body, because contain a lot of fiber and sometimes inhibitors

Depending on the content of nonessential and essential amino acids, proteins are divided into complete and defective. Proteins that contain all the amino acids necessary for the body and in the required quantities are called biologically complete. The highest biological value of proteins in meat, milk, eggs, fish, caviar. Proteins in which one or another amino acid is absent or contains, but in insufficient quantities, are called biologically defective

The body is constantly breaking down proteins. Old cells are destroyed, new ones are formed. Therefore, the body needs a constant supply of protein from food. The need for protein increases sharply in children during the period of increased growth of the body, in pregnant women, during the recovery period after a serious illness, during intensive sports training.

Proteins are broken down in the digestive tract to amino acids and low molecular weight polypeptides, which are absorbed into the bloodstream. With the blood stream, they enter the liver, where some of them undergo deamination and transamination; these processes provide for the synthesis of certain amino acids and proteins. Amino acids are transported from the liver to body tissues, where they are used for protein synthesis. Excess protein from food is converted into carbohydrates and fats. The end products of protein breakdown - urea, ammonia, uric acid, creatinine and others - are excreted from the body in urine and sweat. (Chusov Yu.N. 1998)

Proteins are complex in structure and very specific. Proteins in food and proteins in our body differ significantly in their qualities. If the protein is removed from food and injected directly into the blood, then a person may die. Proteins are made up of protein elements - amino acids, which are formed during the digestion of animal and plant proteins and enter the bloodstream from the small intestine. The cells of a living organism contain more than 20 types of amino acids. The processes of synthesis of huge protein molecules, consisting of chains of amino acids, are continuously proceeding in cells. The combination of these amino acids (all or part of them), linked in chains in a different sequence, and determines the countless variety of proteins.

Amino acids are divided into essential and non-essential. Indispensable are those that the body receives only with food. Replaceable ones can be synthesized in the body from other amino acids. The value of food proteins is determined by the content of amino acids. That is why proteins from food are divided into two groups: complete, containing all essential amino acids, and defective, which lack some essential amino acids. Animal proteins are the main source of complete proteins. Vegetable proteins (with rare exceptions) are defective.

In tissues and cells, the destruction and synthesis of protein structures is continuously going on. In a conditionally healthy body of an adult, the amount of decomposed protein is equal to the amount of synthesized protein. Since the balance of protein in the body is of great practical importance, many methods have been developed for its study. The protein balance is determined by the difference between the amount of protein taken from food and the amount of protein that has undergone destruction during this time. The protein content of foods varies.

The body's metabolism is regulated by nerve centers located in the diencephalon. When some nuclei of this part of the brain are damaged, protein metabolism increases, its balance becomes negative, as a result of which a sharp depletion occurs. The nervous system affects protein metabolism through the hormones of the thyroid gland, the anterior pituitary gland (growth hormone) and other endocrine glands. Proteins play a special role in the vital processes of the body, since neither carbohydrates nor lipids can replace them in the reproduction of the basic structural elements of the cell, as well as in the formation of such important substances as enzymes and hormones. However, protein synthesis from inorganic

Proteins play an extremely important role in human nutrition, since they are the main constituent part of the cells of all organs and tissues of the body.

The main purpose of food proteins is to build new cells and tissues that support the development of young growing organisms. In adulthood, when the growth processes have already been fully completed, there remains a need for the regeneration of worn out, obsolete cells. For this purpose, protein is required, and in proportion to the wear of the tissues. It has been established that the higher the muscle load, the greater the need for regeneration and, accordingly, for protein.

Proteins are complex nitrogen-containing biopolymers, the monomers of which are amino acids.

Proteins in the human body perform several important functions - plastic, catalytic, hormonal, specificity and transport. The most important function of food proteins is to provide the body with plastic material. The human body is practically devoid of protein reserves. Their only source is food proteins, as a result of which they belong to the irreplaceable components of the diet.

In many countries, the population is deficient in proteins. In this regard, the search for new unconventional methods of obtaining it becomes an important task.

Among plant foods, legumes are distinguished by a significant protein content. Before the period of potato cultivation in Europe, legumes were one of the main parts of the population's food. Until now, in many countries, beans, beans, peas are cultivated on large areas. Soy proteins are rich in all essential amino acids, the rate of which is equal to or exceeds 100% according to the WHO scale; the exception is sulfur-containing amino acids (scat 71%). The digestibility of soy proteins is 90.7%. In terms of anabolic efficiency, they are not inferior to proteins of animal origin.

Proteins cannot be replaced by other nutrients, since their synthesis in the body is possible only from amino acids. At the same time, protein can replace fats and carbohydrates, that is, it can be used for the synthesis of these compounds.

A person gets protein from food. With the introduction of foreign protein substances directly into the blood, bypassing the digestive tract, they not only cannot be used by the body, but also lead to a number of serious complications (fever, convulsions and other phenomena). With the repeated introduction of a foreign protein into the bloodstream, death may occur after 15-20 days. (Solodkov A.S. 2001)

In the absence of high-grade protein nutrition, growth is inhibited, the formation of the skeleton is impaired. With protein starvation, an increased breakdown of proteins of skeletal muscles, liver, blood, intestines, and skin occurs first. The amino acids that are released in this case are used for the synthesis of proteins of the central nervous system, myocardium, and hormones. However, such a redistribution of amino acids cannot make up for the lack of dietary protein, and a natural decrease in the activity of enzymes occurs, the functions of the liver, kidneys, etc. are impaired.

Protein synthesis without B vitamins is markedly reduced. Fats are involved in the transport of proteins. Proteins of various food products differ from each other in amino acid composition, but in total they complement each other. Therefore, to provide the body with the entire spectrum of amino acids in human nutrition, a wide range of protein products of animal and plant origin should be used. Various protein combinations can be used to supply the body with an optimal amino acid composition. For example: cheesecakes with cottage cheese, meat pies, milk rice porridge. The biological value of proteins used in nutrition determines their required amount to meet the needs of the body.

The better the amino acid composition of the protein, the faster it is digested and absorbed, the less it is required. The high species-specificity of proteins that make up organs and tissues can be explained by the fact that under conditions of complete starvation in the body of an adult, 22-24 g of tissue proteins are broken down to cover the minimum physiological costs with the formation of a negative nitrogen balance. For the resynthesis of this amount of protein, it is necessary to introduce 50-70 g of protein with food. This big difference depends on the biological value of the proteins. Insufficient protein content in the human diet leads to the breakdown of tissue proteins, which ultimately leads to a negative nitrogen balance, depletion of the body. This manifests itself in the form of a delay in growth and mental development in children, a decrease in conditioned reflex excitability of the central nervous system, a decrease in resistance to stress and infections, inhibition of hormonal activity, body weight deficiency, fatty liver infiltration, poor wound healing, and decreased immunity. Protein deficiency contributes to the development of pellagra, which is manifested by trophic disorders, muscle weakness, and edema. Against the background of protein deficiency, children develop kwashiorkor disease. Its symptoms are: edema, growth retardation, osteoporosis, muscle weakness, diarrhea, polyuria.

Alimentary protein deficiency can occur when the principles of rational nutrition are violated, against the background of acute and chronic diseases of the intestines, other organs and systems. If the digestion processes are disturbed, the absorption and assimilation of fats and carbohydrates deteriorates, and this contributes to the enhanced breakdown of protein to replenish energy expenditures. Increased protein consumption occurs in infectious diseases, tuberculosis, trauma, operations, burns, tumor processes, massive blood loss. Special diet can prevent protein deficiency.

At the same time, excess protein in the diet is also harmful to the body. With an excessive intake of protein with food in the body, putrefactive processes in the intestine are intensified, an overstrain in the activity of the liver and kidneys occurs due to the products of protein metabolism, an overstrain of the secretory function of the digestive glands.

The protein requirement for adults is 1 g per 1 kg of normal body weight per day, an average of 70 g per day. Animal proteins should make up 50-55% of the total protein.

The need for protein increases to 100-120 g per day during the recovery period after severe infections, fractures, diseases of the digestive system, suppurative lung diseases, taking corticosteroid and anabolic hormones. Protein is limited in acute nephritis, kidney and liver failure, gout and some other diseases. (Baeshko A.A. 1999).

In the digestive tract, proteins are broken down by enzymes to amino acids and they are absorbed in the small intestine. Simultaneously with amino acids, the simplest peptides can also be partially absorbed. Cells synthesize their own protein from amino acids and the simplest peptides, which is characteristic only for this organism. Proteins cannot be replaced by other nutrients, since their synthesis in the body is possible only from amino acids.

The biological value of proteins. In various natural sources of protein (plant and animal), there are more than 80 amino acids. The foods that humans use contain only 20 amino acids.

In humans, a relative protein balance is constantly maintained, that is, how much protein is consumed, so much should be supplied with food. The amount of breaking down protein can be judged by the amount of nitrogen excreted from the body, since it is almost not contained in other nutrients. The protein balance in the body is judged by the nitrogen balance, that is, by the ratio of the amount of nitrogen introduced into the body and nitrogen removed from it. If this quantity is the same, then such a state is called nitrogen equilibrium, or balance. It is observed in a healthy adult, normally eating person. The condition in which the absorption of nitrogen exceeds its excretion is called a positive nitrogen balance. It is typical for a growing organism, as well as for athletes, whose training is aimed at the development of skeletal muscles, their strength qualities. In some diseases and during starvation, nitrogen is absorbed less than it is spent. This condition is called negative nitrogen balance. Normal vital functions of the organism are possible only with nitrogenous equilibrium or positive nitrogenous balance.

1.3 Nitrogen balance

Nitrogen balance is the ratio between the amount of nitrogen contained in food ingested and the amount of nitrogen excreted from the body. If both of these values are equal, the body is in a state of nitrogen equilibrium. When tissue proteins are broken down in the body without their complete restoration, a negative nitrogen balance occurs - more nitrogen is excreted from the body than it comes in. Negative nitrogen balance under the body is observed with complete and partial protein starvation, as well as with some diseases accompanied by an increase in tissue decay in an adult with complete starvation, an average of 3.71 g of nitrogen is released per day. This corresponds to 23.2 g of degradable protein. Normal activity of an adult organism is possible only with nitrogenous equilibrium or with a positive nitrogenous balance. Nitrogen equilibrium occurs when 60-70 g of protein is introduced into the body, provided there is sufficient intake of fats and carbohydrates. This amount of protein is the protein optimal daily protein intake in the diet of an adult is significantly higher than the protein minimum and fluctuates depending on the metabolic rate and on the nature of the work performed. For persons who are not engaged in physical labor, the protein optimum is on average 109 g. For physical mechanized labor, the protein norm should be increased on average to 122 g. For persons who are physically mechanized or not fully mechanized, the protein norm on average ranges from 140 to 163 g. When a person goes in for sports, his metabolism increases and the breakdown and synthesis of tissue proteins increases. The need for dietary protein increases, reaching 150-160 g, depending on the tastes and habits of each athlete, the protein content in the diet may fluctuate, but under no circumstances should the daily intake be less than 1.5 g per 1 kg of weight.According to some authors, animal proteins have especially of great importance for persons engaged in strength and speed exercises.

The desire of some athletes to consume large amounts of protein (up to 250 and even 300 g per day) is not physiologically justified. With an excessive intake of protein into the body, its nitrogen-free components are used as energy materials, while the components containing nitrogen turn into substances that are not only not indifferent, but even harmful to the organ. So, for example, ammonia, formed from amino acids, is a substance poisonous to the body. The greatest effect is observed when proteins are introduced into the body immediately after a training session or even better before it. In the latter case, the increase in the mass and strength of the working muscles occurs most effectively. (Schmidt 1983).

Nitrogen balance. The amount of protein obtained from food or excreted from the body can be judged by the amount of nitrogen consumed or excreted. Of the nutrients, only proteins contain nitrogen. It is known that its amount in protein is 16%. From this it is easy to calculate that 1 g of nitrogen is contained in 6.25 g of protein (100: 16). Hence, knowing the amount of excreted or consumed nitrogen, it is easy to calculate the corresponding amount of protein.

Nitrogen balance refers to the difference in the amount of nitrogen introduced into the body with food and excreted in urine, feces and sweat. A day of a healthy adult is characterized by a nitrogen balance, at which the nitrogen balance is 0.

The biological value of proteins. Distinguish between biologically complete and defective proteins. The degree of protein value is determined by the amount of amino acids required for the normal course of synthesis processes in the body. Proteins that contain in a certain ratio all the amino acids necessary for this are called complete, and proteins that do not have the required set of amino acids are called defective. The latter include, for example, the protein of corn and barley.

In the digestive tract, proteins are broken down into amino acids, which are absorbed into the bloodstream. Having passed through the vessels of the liver, amino acids are brought to all organs, in the cells of which a protein is synthesized again, but already specific for each of them. For protein synthesis, amino acids, peptides and nucleotide peptides are also used, which are formed during the breakdown of cellular proteins. A nucleotide peptide is a product of incomplete degradation of a protein, consisting of peptides and a nucleotide group. For protein synthesis, amino acids are also used, which are synthesized in the body. In the body, proteins of another type can be synthesized from the breakdown products of proteins of one type.

The intensity of protein synthesis is quite high. Every day in the developing human body, 100 g of proteins are synthesized. However, not all amino acids formed during protein breakdown are used for its synthesis. Part of the amino acids undergoes decomposition, the end products of which are NH3, CO2 and H2O. Neutralization of ammonia is also carried out in the liver through the synthesis of urea - a substance relatively harmless to the body, excreted in the urine. The products of incomplete breakdown of some amino acids can be used in the body as a building material for the synthesis of other amino acids. The body is constantly synthesizing and decaying not only simple proteins, but also complex ones.

The end products of nucleoprotein metabolism are urea, uric acid, carbon dioxide and water. The most important nitrogenous breakdown products of proteins that are excreted in urine and sweat are urea, uric acid and ammonia.

The oxidation of amino acids occurs by the elimination of nitrogen from them in the form of ammonia. Ammonia is highly toxic to the central nervous system and other body tissues. However, ammonia is rendered harmless in the tissues of the liver and brain: in the liver by the formation of urea, in the brain tissue by conversion into glutamine.

The blood of the hepatic vein contains three times less ammonia than the portal vein. Consequently, in the liver, a significant part of the ammonia is converted to urea. Removal of the liver leads to death from ammonia poisoning. Urea, on the other hand, is a relatively harmless product and is excreted in the urine.

Part of the ammonia is rendered harmless by conversion to glutamic acid and glutamine. Only a small amount of ammonia circulates in the blood of healthy people.

If the synthesis of urea in the liver is disturbed, the concentration of ammonia, amino acids and polypeptides in the blood increases, which causes excitement of the central nervous system, the appearance of seizures, confusion and even coma and death. (Schmidt R. 1983)

Section 2. Protein metabolism in various conditions of the body

2 .one. Protein metabolism during muscle activity

Proteins are the main building blocks of cells and tissues. In the diet of a young athlete, whose body grows and forms, the amount of protein food should be sufficient - more than 3 g per day for each kilogram of body weight. With age, this value decreases: so, at the age of 15-17, 2.5 g is sufficient, and from 18 years - 2.0 g or less per 1 kg of body weight. The source of protein is meat, fish, eggs, cheeses, milk, peas, beans, beans, buckwheat and other cereals. (Smirnov V.M. 2002)

Proteins make an insignificant contribution to the energy of muscle activity, since they provide only 10-15% of the total energy consumption of the body. Nevertheless, they play an important role in ensuring the contractile function of skeletal muscles and the heart, in the formation of long-term adaptation to physical activity, in the creation of a certain compositional composition of muscles.

Physical activity causes changes in the processes of synthesis and breakdown of proteins in tissues, especially in skeletal muscles and liver, the degree of their immobility depends on the intensity and duration of physical activity, as well as on the fitness of the body. Changes in interstitial protein metabolism are usually determined by the concentration of individual essential amino acids in the blood, which are not synthesized in the body and are formed during the breakdown of tissue proteins. As a specific indicator of the breakdown of the contractile proteins actin and myosin, 3-methylhistidine is used.

Single physical activity causes the inhibition of protein synthesis and an increase in their catabolism. So, for example, when running on a treadmill for an hour, the rate of protein synthesis in the liver decreased by 20%, and with extreme work - by 65%. This pattern is also observed in skeletal muscles.

Under the influence of physical exertion, the breakdown of muscle proteins (mainly structural) increases, although certain types of loads increase the breakdown of contractile proteins.

With systematic physical exertion, adaptive protein synthesis is activated in muscles and other tissues, the content of structural and contractile proteins, as well as myoglobin and many enzymes, increases. This leads to an increase in muscle mass, the cross-section of muscle fibers, which is considered muscle hypertrophy. An increase in the amount of enzymes creates favorable conditions for expanding the energy potential in working muscles, which, in turn, enhances the biosynthesis of muscle proteins after physical exertion and improves human motor abilities.

Loads of a high-speed and strength nature to a greater extent enhance the synthesis of myofibrillar proteins in muscles, and loads on endurance - mitochondrial enzymes that provide the processes of aerobic synthesis of ATP. The type of physical activity (swimming, running) also largely determines the magnitude of changes in protein synthesis.

Under the influence of training in skeletal muscles, an adaptive activation of all the main links of protein synthesis occurs, leading to a general increase in the cellular protein-synthesizing potential. In the induction of adaptive protein synthesis during training, an important role belongs to hormones: glucocorticoids, adrenaline, growth hormone, thyroxine, and insulin. They are involved in ensuring the transition of urgent adaptive responses to long-term adaptation.

The onset of biochemical adaptation is associated with increased activity of a number of enzymes and an increase in the amount of energy substrates. Strengthening energy metabolism leads to the formation of metabolites - inducers of protein synthesis at the genetic level. Inductors can be ADP, AMP, creatine, some amino acids, cyclic AMP, etc. An increase in genome activity causes an increase in translation or synthesis of structural contractile or enzymatic proteins, which, in turn, provides a high functional activity of the muscles of a trained body when performing muscle work.

Amino acids, the breakdown products of endogenous proteins, make a significant contribution to the energetics of muscle activity, especially long-term activity. Their number in tissues during long-term physical work can increase 20-25 times. These amino acids are oxidized and replenish ATP, or are involved in the process of neoplasm of glucose and help maintain its level in the blood, as well as the level of glycogen in the liver and skeletal muscles.

The processes of protein breakdown and amino acid oxidation are accompanied by increased formation of ammonia (NH3) during muscle activity, which binds in the liver in the urea synthesis cycle and is excreted from the body. Therefore, physical activity causes an increase in the content of urea in the blood, and the normalization of its level during the rest period indicates the restoration of the processes of decay and synthesis of proteins in tissues.

Systematic physical exercise has a pronounced specific effect on the metabolism of proteins in the body. Physical training aimed at developing strength increases muscle mass and increases the content of actin and myosin in the muscles. At the same time, training sessions aimed at developing endurance have little effect on muscle mass, but they increase the content of mitochondrial proteins in muscle tissue, especially those associated with oxidative metabolism. These changes are selective and depend on the direction of training influences.

Exercise can also have acute effects: an increase in muscle mass and an increase in the content of actin and myosin in the muscles. At the same time, training sessions aimed at developing endurance have little effect on muscle mass, but they increase the content of mitochondrial proteins in muscle tissue, especially those associated with oxidative metabolism. These changes are selective and depend on the direction of training influences.

Exercise can also have acute effects on protein metabolism. The reactions manifested in response to tense muscular activity may be similar in many respects to the reactions characteristic of the acute phase during infection or injury.

Muscle has a limited ability to oxidize amino acids. So, skeletal muscles of mammals can oxidize only six of them - alanine, aspartate, glutamate, leucine, isoleucine and valine (the last three are branched-chain amino acids), and their oxidation by muscles leads to the problem of elimination of amino groups, some of which are in the reaction transamination is carried over to pyruvate to form alanine. The latter enters the liver and is then included in the urea cycle (Fig. 1).

In inactive muscles, the contribution of amino acid oxidation to ATP resynthesis is no more than 10% of the total amount of energy sources used, however, with physical exertion, the value of this contribution decreases. In the context of limiting the supply of other types of "fuel", the oxidation of amino acids for energy supply again acquires more significant importance. In this case, the rate of oxidation of individual amino acids increases unevenly (for example, the rate of oxidation of leucine can increase fivefold). Nevertheless, the degree of increase in the rate of leucine oxidation requires clarification, since the use of isotopic techniques in this case does not allow obtaining sufficiently reliable data.

Figure 1. Oxidation of BCAAs as an important energy source for contracting muscles (amino groups from these amino acids are transported to the liver for inclusion in the urea cycle)

structure function value protein

With prolonged physical activity of moderate intensity, the contribution of protein metabolism to energy production is, obviously, no more than 6% of the total energy requirement. However, in the food of the inhabitants of the western regions of the planet, on average, about 12-15% of the energy consumed falls on the share of proteins. This fact allows us to assume that systematic muscular activity in a smaller cost increases the need for protein intake in comparison with the need for carbohydrates and fats. In very strenuous physical activities, when bodybuilding athletes use large amounts of protein supplements to gain muscle mass, there is still no evidence that such a diet can stimulate the absorption of excessively consumed protein by the body's tissues. However, supplements of this kind are still popular and are used against the background of increased consumption of other substances (including insulin and such L-agonists as maple-buterol), which promote the entry of amino acids into muscles and the formation of proteins from them.

2.2 Amino acid metabolism disorder

The most common diseases associated with a violation of amino acid metabolism are phenylketonuria and albinism.

Normally, the amino acid phenylalanine (FA) is converted by the enzyme phenylalanine hydroxylase into the amino acid tyrosine, which in turn, under the action of the enzyme tyrosinase, can be converted into the pigment melanin. When the activity of these enzymes is impaired, hereditary human diseases phenylketonuria and albinism develop.

Phenylketonuria (PKU) occurs in various populations of people with a frequency of 1: 6000-1: 10,000. It is inherited in an autosomal recessive manner; patients - recessive homozygotes (aa). The mutant gene, which is responsible for the synthesis of the enzyme phenylalanine hydroxylase, has been mapped (12q22-q24), identified and sequenced (nucleotide sequence determined).

Phenylalanine is one of the essential amino acids. Only part of FA is used for protein synthesis; most of this amino acid is oxidized to tyrosine. If the enzyme phenylalanine hydroxylase is not active, then FA does not convert to tyrosine, but accumulates in blood serum in large quantities in the form of phenylpyruvic acid (FPVA), which is excreted in urine and sweat, as a result of which a “mouse” odor emanates from patients. A high concentration of FPVK leads to disruption of the formation of the myelin sheath around axons in the central nervous system.

Children with phenylketonuria are born healthy, but in the first weeks of life they develop clinical manifestations of the disease. FPVK is a neurotropic poison, as a result of which excitability, muscle tone increase, hyperreflexia, tremor, convulsive epileptiform seizures develop. Later, violations of higher nervous activity, mental retardation, microcephaly join. Patients have weak pigmentation due to a violation of melanin synthesis.

Albinism occurs in different populations with varying frequency - from 1: 5000 to 1:25 000. Its most common form - oculocutaneous tyrosinase-negative albinism - is inherited in an autosomal recessive manner. The main clinical manifestations of albinism at any age are the absence of melanin in skin cells (its milky white color), very light hair, light gray or light blue iris of the eyes, red pupil, hypersensitivity to UV radiation (causes inflammatory skin diseases ). Patients have no pigment spots on the skin, visual acuity is reduced. Diagnosis of the disease is not difficult.

Diseases of amino acid metabolism

The largest group of hereditary metabolic diseases. Almost all of them are inherited in an autosomal recessive manner. The cause of the disease is the lack of one or another enzyme responsible for the synthesis of amino acids. These include:

· Phenylketonuria - a violation of the conversion of phenylalanine to tyrosine due to a sharp decrease in the activity of phenylalanine hydroxylase;

Phenylketonurimia (phenylpyruvic oligophrenia) is a hereditary disease of the group of fermentopathies associated with a violation of the metabolism of amino acids, mainly phenylalanine; accompanied by the accumulation of phenylalanine and its toxic products, which leads to severe damage to the central nervous system, manifested in the form of impaired mental development. In most cases (classical form), the disease is associated with a sharp decrease or complete absence of the activity of the hepatic enzyme phenylalanine-4-hydroxylase, which normally catalyzes the conversion of phenylalanine to tyrosine.

As a result of the metabolic block, side pathways of phenylalanine metabolism are activated, and the body accumulates its toxic derivatives - phenylpyruvic and phenyl lactic acids, which are practically not formed normally. In addition, phenylethylamine and orthophenyl acetate, which are almost completely absent in the norm, are also formed, an excess of which causes a violation of lipid metabolism in the brain. This leads to a progressive decrease in intelligence in such patients to the point of idiocy.

· Alkaptonuria - violation of tyrosine metabolism due to reduced activity of the enzyme homogentisinase and accumulation of homotentisinic acid in the tissues of the body;

Oculocutaneous albinism - due to the lack of synthesis of the enzyme tyrosinase.

Alcaptomurimia is a recessively inherited disease caused by the loss of functions of homogentesic acid oxidase.

With alkaptonuria, ochronosis is noted - a darkening of cartilaginous tissues and a rapid darkening of urine when it is alkalized due to the oxidation of homogentesic acid with the formation of dark-colored pigments.

Under normal conditions, homogentesic acid, an intermediate product of the breakdown of tyrosine and phenylalanine, is converted into maleyl acetoacetic acid, from which fumaric and acetoxy acids are ultimately formed, entering other biochemical cycles. Due to a defect in the enzyme, this process is inhibited, and the excess homogentesic acid is converted by polyphenol oxidase into quinone polyphenols (alkapone), which are excreted by the kidneys. Alcapton, which is not completely excreted by urine, is deposited in cartilage and other connective tissue, causing them to darken and increase fragility. Most often, pigmentation of the sclera and ear cartilage appears ahead.

There is no radical treatment, symptomatic therapy and large doses of ascorbic acid are used.

Homocystinuria. Etiology and pathogenesis. Hereditary enzymopathy.

At the heart of the disease is a deficiency of the enzyme cystathionine synthetase, as a result of which methionine and homocystine accumulate in the blood, which have a toxic effect on the child's body. There are two forms of homocystinuria: pyridoxine-dependent and pyridoxine-resistant. At the 2nd year of life, symptoms of the disease may be absent. Then there is some lag in physical and mental development. Bone deformities, lens subluxation, neurological symptoms, and body weight deficit are noted. The content of homocystine is increased in urine. The blood contains high levels of homocystine and methionine.

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