Proteins

Proteins are macromolecular natural substances consisting of a chain of amino acids linked by a peptide bond. The most important role of these compounds is the regulation of chemical reactions in the body (enzymatic role). In addition, they perform protective, hormonal, structural, nutritional, energy functions.

By structure, proteins are divided into simple (proteins) and complex (proteids). The amount of amino acid residues in the molecules is different: myoglobin is 140, insulin is 51, which explains the high molecular weight of the compound (Mr), which ranges from 10 000 to 3 000 000 Dalton.

Proteins account for 17% of the total human weight: 10% are skin, 20% are cartilage, bones, and 50% are muscles. Despite the fact that the role of proteins and proteids has not been thoroughly studied today, the functioning of the nervous system, the ability to grow, reproduce the body, the flow of metabolic processes at the cellular level is directly related to the activity of amino acids.

History of discovery

The process of studying proteins originates in the XVIII century, when a group of scientists led by French chemist Antoine Francois de Furcroix investigated albumin, fibrin, gluten. As a result of these studies, proteins were summarized and isolated into a separate class.

In 1836, for the first time, Mulder proposed a new model of the chemical structure of proteins based on the theory of radicals. It remained generally accepted until the 1850s. The modern name of the protein – protein – the compound received in 1838. And by the end of the XNUMXth century, the German scientist A. Kossel made a sensational discovery: he came to the conclusion that amino acids are the main structural elements of the “building components”. This theory was experimentally proved at the beginning of the XNUMXth century by the German chemist Emil Fischer.

In 1926, an American scientist, James Sumner, in the course of his research, discovered that the enzyme urease produced in the body belongs to proteins. This discovery made a breakthrough in the world of science and led to the realization of the importance of proteins for human life. In 1949, an English biochemist, Fred Sanger, experimentally derived the amino acid sequence of the hormone insulin, which confirmed the correctness of thinking that proteins are linear polymers of amino acids.

In the 1960s, for the first time on the basis of X-ray diffraction, the spatial structures of proteins at the atomic level were obtained. The study of this high-molecular organic compound continues to this day.

Protein structure

The main structural units of proteins are amino acids, consisting of amino groups (NH2) and carboxyl residues (COOH). In some cases, nitric-hydrogen radicals are associated with carbon ions, the number and location of which determine the specific characteristics of peptide substances. At the same time, the position of carbon in relation to the amino group is emphasized in the name with a special prefix: alpha, beta, gamma.

For proteins, alpha-amino acids act as structural units, since only they, when elongating the polypeptide chain, give protein fragments additional stability and strength. Compounds of this type are found in nature in the form of two forms: L and D (except for glycine). Elements of the first type are part of the proteins of living organisms produced by animals and plants, and the second type are part of the structures of peptides formed by non-ribosomal synthesis in fungi and bacteria.

The building blocks of proteins are linked together by a polypeptide bond, which is formed by linking one amino acid to the carboxyl of another amino acid. Short structures are usually called peptides or oligopeptides (molecular weight 3-400 daltons), and long ones, consisting of more than 10 amino acids, polypeptides. Most often, protein chains contain 000 – 50 amino acid residues, and sometimes 100 – 400. Proteins form specific spatial structures due to intramolecular interactions. They are called protein conformations.

There are four levels of protein organization:

1. The primary is a linear sequence of amino acid residues linked together by a strong polypeptide bond.
2. Secondary – the ordered organization of protein fragments in space into a spiral or folded conformation.
3. Tertiary – a way of spatial laying of a helical polypeptide chain, by folding the secondary structure into a ball.
4. Quaternary – collective protein (oligomer), which is formed by the interaction of several polypeptide chains of a tertiary structure.

The shape of the structure of the protein is divided into 3 groups:

• fibrillary;
• globular;
• membrane.

The first type of proteins is cross-linked threadlike molecules that form long-lasting fibers or layered structures. Given that fibrillar proteins are characterized by high mechanical strength, they perform protective and structural functions in the body. Typical representatives of these proteins are hair keratins and tissue collagens.

Globular proteins consist of one or more polypeptide chains folded into a compact ellipsoidal structure. These include enzymes, blood transport components, and tissue proteins.

Membrane compounds are polypeptide structures that are embedded in the shell of cell organelles. These compounds perform the function of receptors, passing the necessary molecules and specific signals through the surface.

To date, there is a huge variety of proteins, determined by the number of amino acid residues included in them, the spatial structure and the sequence of their location.

However, for the normal functioning of the body, only 20 alpha-amino acids of the L-series are required, 8 of which are not synthesized by the human body.

Physical and chemical properties

The spatial structure and amino acid composition of each protein determine its characteristic physicochemical properties.

Proteins are solids that form colloidal solutions when interacting with water. In aqueous emulsions, proteins are present in the form of charged particles, since the composition includes polar and ionic groups (–NH2, –SH, –COOH, –OH). The charge of a protein molecule depends on the ratio of carboxyl (–COOH), amine (NH) residues and the pH of the medium. Interestingly, the structure of proteins of animal origin contains more dicarboxylic amino acids (glutamic and aspartic), which determines their negative potential in aqueous solutions.

Some substances contain a significant amount of diamino acids (histidine, lysine, arginine), as a result of which they behave in liquids as protein cations. In aqueous solutions, the compound is stable due to the mutual repulsion of particles with like charges. However, a change in the pH of the medium entails a quantitative modification of the ionized groups in the protein.

In an acidic environment, the decomposition of carboxyl groups is suppressed, which leads to a decrease in the negative potential of the protein particle. In alkali, on the contrary, the ionization of amine residues slows down, as a result of which the positive charge of the protein decreases.

At a certain pH, the so-called isoelectric point, alkaline dissociation is equivalent to acidic, as a result of which the protein particles aggregate and precipitate. For most peptides, this value is in a slightly acidic environment. However, there are structures with a sharp predominance of alkaline properties. This means that the bulk of proteins fold in an acidic environment, and a small part in an alkaline one.

At the isoelectric point, proteins are unstable in solution and, as a result, coagulate easily when heated. When acid or alkali is added to the precipitated protein, the molecules are recharged, after which the compound dissolves again. However, proteins retain their characteristic properties only at certain pH parameters of the medium. If the bonds that hold the spatial structure of the protein are somehow destroyed, then the ordered conformation of the substance is deformed, as a result of which the molecule takes the form of a random chaotic coil. This phenomenon is called denaturation.

The change in the properties of the protein leads to the impact of chemical and physical factors: high temperature, ultraviolet irradiation, vigorous shaking, combination with protein precipitants. As a result of denaturation, the component loses its biological activity, the lost properties are not returned.

Proteins give color in the course of hydrolysis reactions. When the peptide solution is combined with copper sulfate and alkali, a lilac color appears (biuret reaction), when proteins are heated in nitric acid – a yellow tint (xantoprotein reaction), when interacting with a nitrate solution of mercury – raspberry color (Milon reaction). These studies are used to detect protein structures of various types.

Types of proteins possible synthesis in the body

The value of amino acids for the human body can not be underestimated. They perform the role of neurotransmitters, they are necessary for the correct functioning of the brain, supply energy to the muscles, and control the adequacy of the performance of their functions with vitamins and minerals.

The main significance of the connection is to ensure the normal development and functioning of the body. Amino acids produce enzymes, hormones, hemoglobin, antibodies. The synthesis of proteins in living organisms is constantly.

However, this process is suspended if the cells lack an at least one essential amino acid. Violation of the formation of proteins leads to digestive disorders, slower growth, psycho-emotional instability.

Most of the amino acids are synthesized in the human body in the liver. However, there are such compounds that must necessarily come daily with food.

This is due to the distribution of amino acids in the following categories:

• irreplaceable;
• semi-replaceable;
• replaceable.

Each group of substances has specific functions. Consider them in detail.

Essential Amino Acids

A person is not able to produce organic compounds of this group on his own, but they are necessary to maintain his life.

Therefore, such amino acids have acquired the name “essential” and must be regularly supplied from the outside with food. Protein synthesis without this building material is impossible. As a result, the lack of at least one compound leads to metabolic disorders, a decrease in muscle mass, body weight, and a stop in protein production.

The most significant amino acids for the human body, in particular for athletes and their importance.

1. Valin. It is a structural component of a branched chain protein (BCAA) .It is an energy source, participates in metabolic reactions of nitrogen, restores damaged tissues, and regulates glycemia. Valine is necessary for the flow of muscle metabolism, normal mental activity. Used in medical practice in combination with leucine, isoleucine for the treatment of the brain, liver, injured as a result of drug, alcohol or drug intoxication of the body.
2. Leucine and Isoleucine. Reduce blood glucose levels, protect muscle tissue, burn fat, serve as catalysts for the synthesis of growth hormone, restore skin and bones. Leucine, like valine, is involved in energy supply processes, which is especially important for maintaining the body’s endurance during grueling workouts. In addition, isoleucine is needed for the synthesis of hemoglobin.
3. Threonine. It prevents fatty degeneration of the liver, participates in protein and fat metabolism, the synthesis of collagen, elastane, the creation of bone tissue (enamel). Amino acid increases immunity, the body’s susceptibility to ARVI diseases. Threonine is found in the skeletal muscles, central nervous system, heart, supporting their work.
4. Methionine. It improves digestion, participates in the processing of fats, protects the body from the harmful effects of radiation, reduces the manifestations of toxicosis during pregnancy, and is used to treat rheumatoid arthritis. The amino acid is involved in the production of taurine, cysteine, glutathione, which neutralize and remove toxic substances from the body. Methionine helps reduce histamine levels in cells in people with allergies.
5. Tryptophan. Stimulates the release of growth hormone, improves sleep, reduces the harmful effects of nicotine, stabilizes mood, is used for the synthesis of serotonin. Tryptophan in the human body is able to turn into niacin.
6. Lysine. Participates in the production of albumins, enzymes, hormones, antibodies, tissue repair and collagen formation. This amino acid is part of all proteins and is necessary to reduce the level of triglycerides in the blood serum, normal bone formation, full absorption of calcium and thickening of the hair structure. Lysine has an antiviral effect, suppressing the development of acute respiratory infections and herpes. It increases muscle strength, supports nitrogen metabolism, improves short-term memory, erection, libido. Thanks to its positive properties, 2,6-diaminohexanoic acid helps keep the heart healthy, prevents the development of atherosclerosis, osteoporosis, and genital herpes. Lysine in combination with vitamin C, proline prevent the formation of lipoproteins, which cause clogging of arteries and lead to cardiovascular pathologies.
7. Phenylalanine. Suppresses appetite, reduces pain, improves mood, memory. In the human body, phenylalanine is able to transform into the amino acid tyrosine, which is vital for the synthesis of neurotransmitters (dopamine and norepinephrine). Due to the compound’s ability to cross the blood-brain barrier, it is often used to treat neurological diseases. In addition, the amino acid is used to combat white foci of depigmentation on the skin (vitiligo), schizophrenia, and Parkinson’s disease.

The lack of essential amino acids in the human body leads to:

• growth retardation;
• violation of the biosynthesis of cysteine, proteins, kidney, thyroid, nervous system;
• dementia;
• weight loss;
• phenylketonuria;
• reduced immunity and blood hemoglobin levels;
• coordination disorder.

When playing sports, the deficiency of the above structural units reduces athletic performance, increasing the risk of injury.

Food Sources of Essential Amino Acids

The table is based on data taken from the United States Agricultural Library – USA National Nutrient Database.

Semi-replaceable

Compounds belonging to this category can be produced by the body only if they are partially supplied with food. Each variety of semi-essential acids performs specific functions that cannot be replaced.

Consider their types.

1. Arginine. It is one of the most important amino acids in the human body. It accelerates the healing of damaged tissues, lowers cholesterol levels and is needed to maintain the health of the skin, muscles, joints, and liver. Arginine increases the formation of T-lymphocytes, which strengthen the immune system, acts as a barrier, preventing the introduction of pathogens. In addition, the amino acid promotes detoxification of the liver, lowers blood pressure, slows down the growth of tumors, resists the formation of blood clots, increases potency and enhances blood vessels. Participates in nitrogen metabolism, creatine synthesis and is indicated for people who want to lose weight and gain muscle mass. Arginine is found in seminal fluid, connective tissue of the skin and hemoglobin. Deficiency of the compound in the human body is dangerous for the development of diabetes mellitus, infertility in men, delayed puberty, hypertension, and immunodeficiency. Natural sources of arginine: chocolate, coconut, gelatin, meat, dairy, walnut, wheat, oats, peanuts, soy.
2. Histidine. Included in all tissues of the human body, enzymes. Participates in the exchange of information between the central nervous system and peripheral departments. Histidine is necessary for normal digestion, since the formation of gastric juice is possible only with its participation. In addition, the substance prevents the occurrence of autoimmune, allergic reactions. The lack of a component causes hearing loss, increases the risk of developing rheumatoid arthritis. Histidine is found in cereals (rice, wheat), dairy products, and meat.
3. Tyrosine. Promotes the formation of neurotransmitters, reduces the pain of the premenstrual period, contributes to the normal functioning of the whole organism, acts as a natural antidepressant. The amino acid reduces dependence on narcotic, caffeine drugs, helps control appetite and serves as an initial component for the production of dopamine, thyroxine, epinephrine. In protein synthesis, tyrosine partially replaces phenylalanine. In addition, it is needed for the synthesis of thyroid hormones. Amino acid deficiency slows down metabolic processes, lowers blood pressure, increases fatigue. Tyrosine is found in pumpkin seeds, almonds, oatmeal, peanuts, fish, avocados, soybeans.
4. Cystine. It is found in beta-keratin – the main structural protein of hair, nail plates, skin. The amino acid is absorbed as N-acetyl cysteine ​​and is used in the treatment of smoker’s cough, septic shock, cancer, and bronchitis. Cystine maintains the tertiary structure of peptides, proteins, and also acts as a powerful antioxidant. It binds destructive free radicals, toxic metals, protects cells from x-rays and radiation exposure. The amino acid is part of somatostatin, insulin, immunoglobulin. Cystine can be obtained from the following foods: broccoli, onions, meat products, eggs, garlic, red peppers.

A distinctive feature of semi-essential amino acids is the possibility of their use by the body to form proteins instead of methionine, phenylalanine.

Interchangeable

Organic compounds of this class can be produced by the human body independently, covering the minimum needs of internal organs and systems. Replaceable amino acids are synthesized from metabolic products and absorbed nitrogen. To replenish the daily norm, they must be daily in the composition of proteins with food.

Consider which substances belong to this category:

1. Alanine. Used as a source of energy, removes toxins from the liver, accelerates the conversion of glucose. Prevents the breakdown of muscle tissue due to the alanine cycle, presented in the following form: glucose – pyruvate – alanine – pyruvate – glucose. Thanks to these reactions, the building component of the protein increases energy reserves, prolonging the life of cells. Excess nitrogen during the alanine cycle is eliminated from the body in the urine. In addition, the substance stimulates the production of antibodies, ensures the metabolism of acids, sugars and improves immunity. Sources of alanine: dairy products, avocados, meat, poultry, eggs, fish.
2. Glycine. Participates in muscle building, hormone synthesis, increases the level of creatine in the body, promotes the conversion of glucose into energy. Collagen is 30% glycine. Cellular synthesis is impossible without the participation of this compound. In fact, if tissues are damaged, without glycine, the human body will not be able to heal wounds. Sources of amino acids are: milk, beans, cheese, fish, meat.
3. Glutamine. After the conversion of the organic compound into glutamic acid, it penetrates the blood-brain barrier and acts as a fuel for the brain to work. The amino acid removes toxins from the liver, increases GABA levels, maintains muscle tone, improves concentration, and is involved in the production of lymphocytes. L-glutamine preparations are commonly used in bodybuilding to prevent muscle breakdown by transporting nitrogen to the organs, removing toxic ammonia and increasing glycogen stores. The substance is used to relieve symptoms of chronic fatigue, improve the emotional background, treat rheumatoid arthritis, peptic ulcer, alcoholism, impotence, scleroderma. The leaders in the content of glutamine are parsley and spinach.
4. Carnitine. Binds and removes fatty acids from the body. Amino acid enhances the action of vitamins E, C, reduces excess weight, reduces the load on the heart. In the human body, carnitine is produced from glutamine and methionine in the liver and kidneys. It is of the following types: D and L. The greatest value for the body is L-carnitine, which increases the permeability of cell membranes for fatty acids. Thus, the amino acid increases the utilization of lipids, slows down the synthesis of triglyceride molecules in the subcutaneous fat depot. After taking carnitine, lipid oxidation increases, the process of losing adipose tissue is triggered, which is accompanied by the release of energy stored in the form of ATP. L-carnitine enhances the creation of lecithin in the liver, lowers cholesterol levels, and prevents the appearance of atherosclerotic plaques. Despite the fact that this amino acid does not belong to the category of essential compounds, regular intake of the substance prevents the development of heart pathologies and allows you to achieve active longevity. Remember, the level of carnitine decreases with age, so the elderly should first of all additionally introduce a dietary supplement into their daily diet. In addition, most of the substance is synthesized from vitamins C, B6, methionine, iron, lysine. The lack of any of these compounds causes a deficiency of L-carnitine in the body. Natural sources of amino acids: poultry, egg yolks, pumpkin, sesame seeds, lamb, cottage cheese, sour cream.
5. Asparagine. Needed for the synthesis of ammonia, the proper functioning of the nervous system. The amino acid is found in dairy products, asparagus, whey, eggs, fish, nuts, potatoes, poultry meat.
6. Aspartic acid. Participates in the synthesis of arginine, lysine, isoleucine, the formation of a universal fuel for the body – adenosine triphosphate (ATP), which provides energy for intracellular processes. Aspartic acid stimulates the production of neurotransmitters, increases the concentration of nicotinamide adenine dinucleotide (NADH), which is necessary to maintain the functioning of the nervous system and the brain. The compound is synthesized independently, while its concentration in cells can be increased by including the following products in the diet: sugar cane, milk, beef, poultry meat.
7. Glutamic acid. It is the most important excitatory neurotransmitter in the spinal cord. The organic compound is involved in the movement of potassium across the blood-brain barrier into the cerebrospinal fluid and plays a major role in the metabolism of triglycerides. The brain is able to use glutamate as fuel. The body’s need for additional intake of amino acids increases with epilepsy, depression, the appearance of early gray hair (up to 30 years), disorders of the nervous system. Natural sources of glutamic acid: walnuts, tomatoes, mushrooms, seafood, fish, yogurt, cheese, dried fruits.
8. Proline Stimulates collagen synthesis, is needed for the formation of cartilage tissue, accelerates healing processes. Proline sources: eggs, milk, meat. Vegetarians are advised to take an amino acid with nutritional supplements.
9. Serin. Regulates the amount of cortisol in muscle tissue, participates in the synthesis of antibodies, immunoglobulins, serotonin, promotes the absorption of creatine, plays a role in fat metabolism. Serine supports the normal functioning of the central nervous system. The main food sources of amino acids: cauliflower, broccoli, nuts, eggs, milk, soybeans, koumiss, beef, wheat, peanuts, poultry meat.

Thus, amino acids are involved in the course of all vital functions in the human body. Before purchasing food supplements, it is recommended to consult with a specialist. Despite the fact that taking drugs of amino acids, although it is considered safe, but it can exacerbate the hidden health problems.

Types of protein by origin

Today, the following types of protein are distinguished: egg, whey, vegetable, meat, fish.

Consider the description of each of them.

1. Egg. Considered the benchmark among proteins, all other proteins are ranked relative to it because it has the highest digestibility. The composition of the yolk includes ovomucoid, ovomucin, lysocin, albumin, ovoglobulin, coalbumin, avidin, and albumin is the protein component. Raw chicken eggs are not recommended for people with digestive disorders. This is due to the fact that they contain an inhibitor of the enzyme trypsin, which slows down the digestion of food, and the protein avidin, which attaches the vital vitamin H. The resulting compound is not absorbed by the body and is excreted. Therefore, nutritionists insist on the use of egg white only after heat treatment, which releases the nutrient from the biotin-avidin complex and destroys the trypsin inhibitor. The advantages of this type of protein: it has an average absorption rate (9 grams per hour), high amino acid composition, helps to reduce body weight. The disadvantages of chicken egg protein include their high cost and allergenicity.
2. Milk whey. Proteins in this category have the highest breakdown rate (10-12 grams per hour) among whole proteins. After taking products based on whey, within the first hour, the level of peptides and amino acids in the blood increases dramatically. At the same time, the acid-forming function of the stomach does not change, which eliminates the possibility of gas formation and disruption of the digestive process. The composition of human muscle tissue in terms of the content of essential amino acids (valine, leucine and isoleucine) is closest to the composition of whey proteins. This type of protein lowers cholesterol, increases the amount of glutathione, has a low cost relative to other types of amino acids. The main disadvantage of whey protein is the rapid absorption of the compound, which makes it advisable to take it before or immediately after training. The main source of protein is sweet whey obtained during the production of rennet cheeses. Distinguish concentrate, isolate, whey protein hydrolyzate, casein. The first of the obtained forms is not distinguished by high purity and contains fats, lactose, which stimulates gas formation. The protein level in it is 35-70%. For this reason, whey protein concentrate is the cheapest form of building block in sports nutrition circles. Isolate is a product with a higher level of purification, it contains 95% protein fractions. However, unscrupulous manufacturers sometimes cheat by providing a mixture of isolate, concentrate, hydrolyzate as whey protein. Therefore, the composition of the supplement should be carefully checked, in which the isolate should be the only component. Hydrolyzate is the most expensive type of whey protein, which is ready for immediate absorption and quickly penetrates muscle tissue. Casein, when it enters the stomach, turns into a clot, which splits for a long time (4-6 grams per hour). Due to this property, protein is included in infant formulas, since it enters the body stably and evenly, while an intense flow of amino acids leads to deviations in the development of the baby.
3. Vegetable. Despite the fact that the proteins in such products are incomplete, in combination with each other they form a complete protein (the best combination is legumes + grains). The main suppliers of building material of plant origin are soy products that fight osteoporosis, saturate the body with vitamins E, B, phosphorus, iron, potassium, zinc. When consumed, soy protein lowers cholesterol levels, solves problems associated with prostate enlargement, and reduces the risk of developing malignant neoplasms in the breast. It is indicated for people suffering from intolerance to dairy products. For the production of additives, soy isolate (contains 90% protein), soy concentrate (70%), soy flour (50%) are used. The rate of protein absorption is 4 grams per hour. The disadvantages of the amino acid include: estrogenic activity (due to this, the compound should not be taken by men in large doses, since reproductive dysfunction may occur), the presence of trypsin, which slows down digestion. Plants containing phytoestrogens (non-steroidal compounds similar in structure to female sex hormones): flax, licorice, hops, red clover, alfalfa, red grapes. Vegetable protein is also found in vegetables and fruits (cabbage, pomegranates, apples, carrots), cereals and legumes (rice, alfalfa, lentils, flax seeds, oats, wheat, soy, barley), drinks (beer, bourbon). Often in sports The diet uses pea protein. It is a highly purified isolate containing the highest amount of the amino acid arginine (8,7% per gram of protein) relative to whey, soy, casein and egg material. In addition, pea protein is rich in glutamine, lysine. The amount of BCAAs in it reaches 18%. Interestingly, rice protein enhances the benefits of hypoallergenic pea protein, used in the diet of raw foodists, athletes, and vegetarians.
4. Meat. The amount of protein in it reaches 85%, of which 35% are irreplaceable amino acids. Meat protein is characterized by a zero fat content, has a high level of absorption.
5. Fish. This complex is recommended for use by an ordinary person. But it is extremely undesirable for athletes to use protein to cover the daily requirement, since fish protein isolate breaks down to amino acids 3 times longer than casein.

Thus, to reduce weight, gain muscle mass, when working on the relief is recommended to use complex proteins. They provide a peak concentration of amino acids immediately after consumption.

Obese athletes who are prone to fat formation should prefer 50-80% slow protein over fast protein. Their main spectrum of action is aimed at long-term nutrition of the muscles.

Casein absorption is slower than whey protein. Due to this, the concentration of amino acids in the blood increases gradually and is maintained at a high level for 7 hours. Unlike casein, whey protein is absorbed much faster in the body, which creates the strongest release of the compound over a short period of time (half an hour). Therefore, it is recommended to take it to prevent the catabolism of muscle proteins immediately before and immediately after exercise.

An intermediate position is occupied by egg white. To saturate the blood immediately after exercise and maintain a high concentration of protein after strength exercises, its intake should be combined with a whey isolate, an amino acid soon. This mixture of three proteins eliminates the shortcomings of each component, combines all the positive qualities. Most compatible with whey soy protein.

Value for man

The role that proteins play in living organisms is so great that it is almost impossible to consider each function, but we will briefly highlight the most important of them.

1. Protective (physical, chemical, immune). Proteins protect the body from the harmful effects of viruses, toxins, bacteria, triggering the mechanism of antibody synthesis. When protective proteins interact with foreign substances, the biological action of pathogens is neutralized. In addition, proteins are involved in the process of fibrinogen coagulation in the blood plasma, which contributes to the formation of a clot and blockage of the wound. Due to this, in case of damage to the bodily cover, the protein protects the body from blood loss.
2. catalytic. All enzymes, the so-called biological catalysts, are proteins.
3. Transport. The main carrier of oxygen is hemoglobin, a blood protein. In addition, other types of amino acids in the process of reactions form compounds with vitamins, hormones, fats, ensuring their delivery to cells, internal organs, and tissues.
4. Nutritious. The so-called reserve proteins (casein, albumin) are the food sources for the formation and growth of the fetus in the womb.
5. Hormonal. Most of the hormones in the human body (adrenaline, norepinephrine, thyroxine, glucagon, insulin, corticotropin, somatotropin) are proteins.
6. Building Keratin – the main structural component of the hair, collagen – connective tissue, elastin – the walls of blood vessels. Proteins of the cytoskeleton give shape to organelles and cells. Most structural proteins are filamentous.
7. Motor. Actin and myosin (muscle proteins) are involved in the relaxation and contraction of muscle tissues. Proteins regulate translation, splicing, the intensity of gene transcription, as well as the process of cell movement through the cycle. Motor proteins are responsible for the movement of the body, the movement of cells at the molecular level (cilia, flagella, leukocytes), intracellular transport (kinesin, dynein).
8. Signal. This function is performed by cytokines, growth factors, hormone proteins. They transmit signals between organs, organisms, cells, tissues.
9. Receptor. One part of the protein receptor receives an annoying signal, the other reacts and promotes conformational changes. Thus, the compounds catalyze a chemical reaction, bind intracellular mediating molecules, serve as ion channels.

In addition to the above functions, proteins regulate the pH level of the internal environment, act as a reserve source of energy, ensure the development, reproduction of the body, form the ability to think.

In combination with triglycerides, proteins are involved in the formation of cell membranes, with carbohydrates in the production of secrets.

Protein synthesis

Protein synthesis is a complex process that takes place in the ribonucleoprotein particles of the cell (ribosomes). Proteins are transformed from amino acids and macromolecules under the control of information encrypted in genes (in the cell nucleus).

Each protein consists of enzyme residues, which are determined by the nucleotide sequence of the genome that encodes this part of the cell. Since DNA is concentrated in the cell nucleus, and protein synthesis takes place in the cytoplasm, information from the biological memory code to ribosomes is transmitted by a special intermediary called mRNA.

Protein biosynthesis occurs in six stages.

1. Transfer of information from DNA to i-RNA (transcription). In prokaryotic cells, genome rewriting begins with the recognition of a specific DNA nucleotide sequence by the RNA polymerase enzyme.
2. Activation of amino acids. Each “precursor” of a protein, using ATP energy, is linked by covalent bonds with a transport RNA molecule (t-RNA). At the same time, t-RNA consists of sequentially connected nucleotides – anticodons, which determine the individual genetic code (triplet-codon) of the activated amino acid.
3. Protein binding to ribosomes (initiation). An i-RNA molecule containing information about a specific protein is linked to a small ribosome particle and an initiating amino acid attached to the corresponding t-RNA. In this case, the transport macromolecules mutually correspond to the i-RNA triplet, which signals the beginning of the protein chain.
4. Elongation of the polypeptide chain (elongation). The buildup of protein fragments occurs by sequential addition of amino acids to the chain, transported to the ribosome using transport RNA. At this stage, the final structure of the protein is formed.
5. Stop the synthesis of the polypeptide chain (termination). The completion of the construction of the protein is signaled by a special triplet of mRNA, after which the polypeptide is released from the ribosome.
6. Folding and protein processing. To adopt the characteristic structure of the polypeptide, it spontaneously coagulates, forming its spatial configuration. After synthesis on the ribosome, the protein undergoes chemical modification (processing) by the enzymes, in particular, phosphorylation, hydroxylation, glycosylation, and tyrosine.

The newly formed proteins contain polypeptide fragments at the end, which act as signals that direct substances to the area of ​​influence.

The transformation of proteins is controlled by operator genes, which, together with structural genes, form an enzymatic group called an operon. This system is controlled by regulator genes with the help of a special substance, which they, if necessary, synthesize. The interaction of this substance with the operator leads to the blocking of the controlling gene, and as a result, the termination of the operon. The signal to resume the operation of the system is the reaction of the substance with inductor particles.

Daily rate

As you can see, the body’s need for proteins depends on age, sex, physical condition, and exercise. The lack of protein in foods leads to disruption of the activity of internal organs.

Exchange in the human body

Protein metabolism is a set of processes that reflect the activity of proteins within the body: digestion, breakdown, assimilation in the digestive tract, as well as participation in the synthesis of new substances required for life support. Given that protein metabolism regulates, integrates, and coordinates most chemical reactions, it is important to understand the major steps involved in protein transformation.

The liver plays a key role in peptide metabolism. If the filtering organ stops participating in this process, then after 7 days a fatal outcome occurs.

The sequence of the flow of metabolic processes.

1. Amino acid deamination. This process is necessary to convert excess protein structures into fats and carbohydrates. During enzymatic reactions, amino acids are modified into the corresponding keto acids, forming ammonia, a by-product of decomposition. The deanimation of 90% of protein structures occurs in the liver, and in some cases in the kidneys. The exception is branched chain amino acids (valine, leucine, isoleucine), which undergo metabolism in the muscles of the skeleton.
2. Urea formation. Ammonia, which was released during the deamination of amino acids, is toxic to the human body. Neutralization of the toxic substance occurs in the liver under the influence of enzymes that convert it into uric acid. After that, urea enters the kidneys, from where it is excreted along with urine. The remainder of the molecule, which does not contain nitrogen, is modified into glucose, which releases energy when it breaks down.
3. Interconversions between replaceable types of amino acids. As a result of biochemical reactions in the liver (reductive amination, transamination of keto acids, amino acid transformations), the formation of replaceable and conditionally essential protein structures, which compensate for their lack in the diet.
4. Synthesis of plasma proteins. Almost all blood proteins, with the exception of globulins, are formed in the liver. The most important of them and predominant in quantitative terms are albumins and blood coagulation factors. The process of protein digestion in the digestive tract occurs through the sequential action of proteolytic enzymes on them to give the breakdown products the ability to be absorbed into the blood through the intestinal wall.

The breakdown of proteins begins in the stomach under the influence of gastric juice (pH 1,5-2), which contains the enzyme pepsin, which accelerates the hydrolysis of peptide bonds between amino acids. After that, digestion continues in the duodenum and jejunum, where pancreatic and intestinal juice (pH 7,2-8,2) containing inactive enzyme precursors (trypsinogen, procarboxypeptidase, chymotrypsinogen, proelastase) enter. The intestinal mucosa produces the enzyme enteropeptidase, which activates these proteases. Proteolytic substances are also contained in the cells of the intestinal mucosa, which is why the hydrolysis of small peptides occurs after final absorption.

As a result of such reactions, 95-97% of proteins are broken down into free amino acids, which are absorbed in the small intestine. With a lack or low activity of proteases, undigested protein enters the large intestine, where it undergoes decay processes.

Protein deficiency

Proteins are a class of high-molecular nitrogen-containing compounds, a functional and structural component of human life. Considering that proteins are responsible for the construction of cells, tissues, organs, the synthesis of hemoglobin, enzymes, peptide hormones, the normal course of metabolic reactions, their lack in the diet leads to disruption of the functioning of all body systems.

Symptoms of protein deficiency:

• hypotension and muscular dystrophy;
• disability;
• reducing the thickness of the skin fold, especially over the triceps muscle of the shoulder;
• drastic weight loss;
• mental and physical fatigue;
• swelling (hidden, and then obvious);
• chilliness;
• a decrease in skin turgor, as a result of which it becomes dry, flabby, lethargic, wrinkled;
• deterioration of the functional state of the hair (loss, thinning, dryness);
• decreased appetite;
• poor wound healing;
• constant feeling of hunger or thirst;
• impaired cognitive functions (memory, attention);
• lack of weight gain (in children).

Remember, signs of a mild form of protein deficiency may be absent for a long time or may be hidden.

However, any phase of protein deficiency is accompanied by a weakening of cellular immunity and an increase in susceptibility to infections.

As a result, patients more often suffer from respiratory diseases, pneumonia, gastroenteritis, and pathologies of the urinary organs. With a prolonged shortage of nitrogenous compounds, a severe form of protein-energy deficiency develops, accompanied by a decrease in the volume of the myocardium, atrophy of the subcutaneous tissue, and depression of the intercostal space.

Consequences of a severe form of protein deficiency:

• slow pulse;
• deterioration in the absorption of protein and other substances due to inadequate synthesis of enzymes;
• decrease in heart volume;
• anemia;
• violation of egg implantation;
• growth retardation (in newborns);
• functional disorders of the endocrine glands;
• hormonal disbalance;
• immunodeficiency states;
• exacerbation of inflammatory processes due to impaired synthesis of protective factors (interferon and lysozyme);
• decrease in respiration rate.

The lack of protein in the dietary intake especially adversely affects the children’s organism: growth slows down, bone formation is disturbed, mental development is delayed.

There are two forms of protein deficiency in children:

1. Insanity (dry protein deficiency). This disease is characterized by severe atrophy of the muscles and subcutaneous tissue (due to protein utilization), growth retardation, and weight loss. At the same time, puffiness, explicit or hidden, is absent in 95% of cases.
2. Kwashiorkor (isolated protein deficiency). At the initial stage, the child has apathy, irritability, lethargy. Then growth retardation, muscle hypotension, fatty degeneration of the liver, and a decrease in tissue turgor are noted. Along with this, edema appears, masking weight loss, hyperpigmentation of the skin, peeling of certain parts of the body, and thinning hair. Often, with kwashiorkor, vomiting, diarrhea, anorexia, and in severe cases, coma or stupor occur, which often end in death.

Along with this, children and adults may develop mixed forms of protein deficiency.

Reasons for the development of protein deficiency

Possible reasons for the development of protein deficiency are:

• qualitative or quantitative imbalance of nutrition (diet, starvation, lean-to-protein menu, poor diet);
• congenital metabolic disorders of amino acids;
• increased protein loss from urine;
• prolonged lack of trace elements;
• violation of protein synthesis due to chronic pathologies of the liver;
• alcoholism, drug addiction;
• severe burns, bleeding, infectious diseases;
• impaired absorption of protein in the intestine.

Protein-energy deficiency is of two types: primary and secondary. The first disorder is due to inadequate intake of nutrients into the body, and the second – a consequence of functional disorders or taking drugs that inhibit the synthesis of enzymes.

With a mild and moderate stage of protein deficiency (primary), it is important to eliminate the possible causes of the development of pathology. To do this, increase the daily intake of proteins (in proportion to the optimal body weight), prescribe the intake of multivitamin complexes. In the absence of teeth or a decrease in appetite, liquid nutrient mixtures are additionally used for probe or self-feeding. If the lack of protein is complicated by diarrhea, then it is preferable for patients to give yoghurt formulations. In no case is it recommended to consume dairy products due to the inability of the body to process lactose.

Severe forms of secondary insufficiency require inpatient treatment, since laboratory testing is necessary to identify the disorder. To clarify the cause of the pathology, the level of soluble interleukin-2 receptor in the blood or C-reactive protein is measured. Plasma albumin, skin antigens, total lymphocyte counts, and CD4+ T-lymphocytes are also tested to help confirm the history and determine the degree of functional dysfunction.

The main priorities of treatment are adherence to a controlled diet, correction of water and electrolyte balance, elimination of infectious pathologies, saturation of the body with nutrients. Considering that a secondary lack of protein can prevent the cure of the disease that provoked its development, in some cases, parenteral or tube nutrition is prescribed with concentrated mixtures. At the same time, vitamin therapy is used in dosages twice the daily requirement of a healthy person.

If the patient has anorexia or the cause of dysfunction has not been identified, drugs that increase appetite are additionally used. To increase muscle mass, the use of anabolic steroids is acceptable (under the supervision of a physician). Restoration of protein balance in adults occurs slowly, over 6-9 months. In children, the period of complete recovery takes 3-4 months.

Remember, for the prevention of protein deficiency, it is important to include protein products of plant and animal origin in your diet each day.

Overdose

The intake of food rich in protein in excess has a negative impact on human health. An overdose of protein in the diet is no less dangerous than a lack of it.

Characteristic symptoms of excess protein in the body:

• exacerbation of kidney and liver problems;
• loss of appetite, breathing;
• increased nervous irritability;
• copious menstrual flow (in women);
• the difficulty of getting rid of excess weight;
• problems with the cardiovascular system;
• increased rotting in the intestines.

You can determine the violation of protein metabolism using nitrogen balance. If the amount of nitrogen taken in and excreted are equal, the person is said to have a positive balance. Negative balance indicates insufficient intake or poor absorption of protein, which leads to the burning of one’s own protein. This phenomenon underlies the development of exhaustion.

A slight excess of protein in the diet, required to maintain a normal nitrogen balance, is not harmful to human health. In this case, excess amino acids are used as an energy source. However, in the absence of physical activity for most people, protein intake in excess of 1,7 grams per 1 kilogram of body weight helps convert excess protein into nitrogenous compounds (urea), glucose, which must be excreted by the kidneys. An excess amount of the building component leads to the formation of an acid reaction of the body, an increase in the loss of calcium. In addition, animal protein often contains purines, which can be deposited in the joints, which is a precursor to the development of gout.

An overdose of protein in the human body is extremely rare. Today, in the normal diet, high-grade proteins (amino acids) are sorely lacking.

F.A.Q.

What are the pros and cons of animal and plant proteins?

The main advantage of animal sources of protein is that they contain all the essential amino acids necessary for the body, mainly in a concentrated form. The disadvantages of such a protein are the receipt of an excess amount of a building component, which is 2-3 times the daily norm. In addition, products of animal origin often contain harmful components (hormones, antibiotics, fats, cholesterol), which cause poisoning of the body by decay products, wash out “calcium” from the bones, create an extra load on the liver.

Vegetable proteins are well absorbed by the body. They do not contain the harmful ingredients that come with animal proteins. However, plant proteins are not without their drawbacks. Most products (except soy) are combined with fats (in seeds), contain an incomplete set of essential amino acids.

Which protein is best absorbed in the human body?

1. Egg, the degree of absorption reaches 95 – 100%.
2. Milk, cheese – 85 – 95%.
3. Meat, fish – 80 – 92%.
4. Soy – 60 – 80%.
5. Grain – 50 – 80%.
6. Bean – 40 – 60%.

This difference is due to the fact that the digestive tract does not produce the enzymes necessary for the breakdown of all types of protein.

What are the recommendations for protein intake?

1. Cover the daily needs of the body.
2. Ensure that different combinations of protein come in with food.
3. Do not abuse the intake of excessive amounts of protein over a long period.
4. Do not eat protein-rich foods at night.
5. Combine proteins of vegetable and animal origin. This will improve their absorption.
6. For athletes before training to overcome high loads, it is recommended to drink protein-rich protein shake. After class, gainer helps to replenish nutrient reserves. Sports supplement raises the level of carbohydrates, amino acids in the body, stimulating the rapid recovery of muscle tissue.
7. Animal proteins should make up 50% of the daily diet.
8. To remove the products of protein metabolism, much more water is required than for the breakdown and processing of other food components. To avoid dehydration, you need to drink 1,5-2 liters of non-carbonated liquid per day. To maintain the water-salt balance, athletes are recommended to consume 3 liters of water.

How much protein can be digested at a time?

Among supporters of frequent feeding, there is an opinion that no more than 30 grams of protein can be absorbed per meal. It is believed that a larger volume loads the digestive tract and it is not able to cope with the digestion of the product. However, this is nothing more than a myth.

The human body in one sitting is able to overcome more than 200 grams of protein. Part of the protein will go to participate in anabolic processes or SMP and will be stored as glycogen. The main thing to remember is that the more protein enters the body, the longer it will be digested, but all will be absorbed.

An excessive amount of proteins leads to an increase in fat deposits in the liver, increased excitability of the endocrine glands and the central nervous system, enhances the processes of decay, and has a negative effect on the kidneys.

Conclusion

Proteins are an integral part of all cells, tissues, organs in the human body. Proteins are responsible for regulatory, motor, transport, energy and metabolic functions. The compounds are involved in the absorption of minerals, vitamins, fats, carbohydrates, increase immunity and serve as a building material for muscle fibers.

A sufficient daily intake of protein (see Table No. 2 “Human Need for Protein”) is the key to maintaining health and well-being throughout the day.