Proteins are macromolecular natural substances, consisting of a chain of amino acids that are 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 (proteins). The number of amino acid residues in the molecules is different: myoglobin - 140, insulin - 51, which explains the high molecular weight of the compound (Mr), which varies from 10,000 to 3,000,000 daltons.
Proteins account for 17% of the total human weight: 10% is skin, 20% is cartilage, bones, and 50% is muscle. 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
- Structure of proteins
- Physical and chemical properties
- Types of proteins possible synthesis in the body
- Essential amino acids
- Dietary sources of essential amino acids
- Semi-essential ]
- Protein species by origin
- Significance for humans
- Protein synthesis
- Daily value
- Metabolism in the human body
- Protein deficiency
- Frequently Asked Questions
The process of studying proteins dates back to the 18th century, when a group of scientists led by the French chemist Antoine Francois de Fourcroix studied albumin, fibrin, and gluten. As a result of these works, proteins were generalized and separated 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 19th 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 20th century by the German chemist Emil Fischer.
In 1926, American scientist James Sumner discovered during research that the enzyme urease produced in the body belongs to proteins. This discovery maderevolution in the world of science and led to the realization of how important proteins are for human life. In 1949, the English biochemist Fred Sanger experimentally deduced 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, the spatial structures of proteins at the atomic level were obtained for the first time on the basis of X-ray diffraction. The study of this high-molecular organic compound continues to this day.
Structure of proteins
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 3400-10000 daltons), and long ones, consisting of more than 50 amino acids, polypeptides. Most often, protein chains contain 100 - 400 amino acid residues, and sometimes 1000 - 1500. Proteins form specific spatial structures due to intramolecular interactions. They are called protein conformations.
There are four levels of protein organization:
- Primary - a linear sequence of amino acid residues interconnected by a strong polypeptide bond.
- Secondary - ordered organization of protein fragments in space into a helical or folded conformation.
- Tertiary - a way of spatial packing of a helical polypeptide chain, by folding the secondary structure into a ball.
- Quaternary is an assembly protein (oligomer), which is formed by the interaction of several polypeptide chains of the tertiary structure.
According to the shape of the structure, proteins are divided into 3 groups:
The first type of proteins are cross-linked filamentous molecules that form continuous 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 organism, 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 characteristics.
Proteins are solid substances, when interacting with water they form colloidal solutions. 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 proteinparticles 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, easily coagulate 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.
Protein properties are changed by 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 during 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 according to the possibility of synthesis in the body
The importance of amino acids for the human body cannot be underestimated. They act as neurotransmitters, they are necessary for the proper 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 compound is to ensure the normal development and functioning of the body. Amino acids produce enzymes, hormones, hemoglobin, antibodies. Synthesis of proteins in living organisms is ongoing.
However, this process stops if even one essential amino acid is missing in the cells. Violation of the formation of proteins leads to digestive disorders, growth retardation, psycho-emotional instability.
Most amino acids are synthesized in the human body in the liver. However, there are compounds that must be supplied daily with food.
This determines the distribution of amino acids into the following categories:
Each group of substances has specific functions. Let's 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 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.
- Valine. It is a structural component of branched chain protein (BCAA). It is a source of energy, participates in nitrogen metabolism, restores damaged tissues, and regulates the level of glycemia. Valine is essential for muscle metabolism and normal mental activity. It is used in medical practice in combination with leucine, isoleucine for the treatment of the brain, liver, affected by drug, alcohol or drug intoxication of the body.
- 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.
- 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.
- 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.
- 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.
- 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 blockage of arteries and lead to cardiovascular pathologies.
- 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, Parkinson's disease.
Lack of essential amino acids in the human body leads to:
- growth retardation;
- violation of the biosynthesis of cysteine, proteins, functioning of the kidneys, thyroid gland, nervous system;
- weight loss;
- decreased immunity and hemoglobin levels in the blood;
- coordination disorder.
In sports, the deficiency of the above structural units reduces athletic performance, increasing the risk of injury.
Food sources of essential amino acids
|Amino acid content per 100 grams of product, grams|
|Sunflower seeds||) 0.348||0.928||1.139||1.659|
|Sesame seeds||0.33||0.73||) 0.75||1.5|
|Dried mung bean||0.26||0.782||1.008||1.847|
|Raw green peas||0.037||0.203||0.195||0.323|
|White faso le||0.277||0.983||1.031||1.865|
|Whole wheat flour||0.174||0.367||0.443||0.898|
|Whole grain bread||0.122||0.248||0.314||0.574|
|Trout, rainbow trout||0.279||1.092||1.148||2.025|
Amino acid content per 100 grams product, grams
|Dried mung bean||1.664||0.286||1.443||1.237|
|Dried chickpeas||1.291||0.253||) 1.034||0.809|
|Green peas, raw||0.317||0.082||0.2||0.235|
|Black beans||1.483||) 0.325||1.168||1.13|
|Whole grain flour||0.359||0.228||0.682||0.564|
|Pasta||0.324||0.236||0.728 [72 6]||0.635|
|Whole grain bread||0.244||0.136||0.403||0.375|
|Swiss cheese||) 2.585||0.784||1.662||2.139|
|White tuna||) 2.437||0.785||1.036||1.367|
The table is based on data taken from the USA National Nutrient Database.
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.
- 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.
- 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.
- 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. Tyrosinefound in pumpkin seeds, almonds, oatmeal, peanuts, fish, avocados, soybeans.
- 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, 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.
The human body can produce organic compounds of this class independently, covering the minimum needs of internal organs and systems. Non-essential amino acids are synthesized from metabolic products and digestible nitrogen. To replenish the daily norm, they must be supplied daily as part of proteins with food.
Consider which substances belong to this category:
- 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.
- 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.
- 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 productionlymphocytes. 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 glutamine content are parsley and spinach.
- Carnitine. Binds and removes fatty acids from the body. The 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, and 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.
- 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.
- 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.
- 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.
- Proline. Stimulates the synthesis of collagen, is needed for the formation of cartilage tissue, accelerates the healing process. Sources of proline: eggs, milk, meat. Vegetarians are recommended to take the amino acid with food supplements.
- 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 all vital functions in the human body. Before purchasing nutritional supplements, it is recommended to consult with a specialist. Despite the fact that taking amino acid preparations, although considered safe, can exacerbate hidden health problems.
Types of protein by origin
Today, the following types of protein are distinguished: egg, whey, vegetable, meat, fish.
Consider a description of each of them.
- 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 problems. 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. Advantages of this type of protein: has an average speedabsorption (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.
- 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.
- 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 used, soy protein lowers cholesterol levels, solves problems associated withprostate enlargement, 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, soybeans, barley ), drinks ( beer, bourbon ). Pea protein is often used in sports nutrition. 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.
- Meat. The amount of protein in it reaches 85%, of which 35% are essential amino acids. Meat protein is characterized by zero fat content, has a high level of absorption.
- 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, and when working on relief, it is recommended to use complex proteins. They provide a peak concentration of amino acids immediately after consumption.
Obese athletes who tend to build fat should prefer 50-80% slow protein over fast protein. Their main spectrum of action is aimed at long-term nutrition of the muscles.
Casein is absorbed more slowly 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, whichcreates the strongest release of the compound for a short period of time (half an hour). Therefore, it is recommended to take it to prevent muscle protein catabolism immediately before and immediately after training.
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.
Significance for humans
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.
- 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.
- Catalytic. All enzymes, the so-called biological catalysts, are proteins.
- 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.
- Nutritious. The so-called reserve proteins (casein, albumin) are sources of nutrition for the formation and growth of the fetus in the womb.
- Hormonal. Most of the hormones in the human body (adrenaline, norepinephrine, thyroxine, glucagon, insulin, corticotropin, somatotropin) are proteins.
- Construction. Keratin is the main structural component of hair, collagen is the connective tissue, elastin is the walls of blood vessels. Cytoskeletal proteins give shape to organelles, cells. Most structural proteins are filamentous.
- Motor. Actin and myosin (muscle proteins) are involved in the relaxation and contraction of muscle tissue. 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).
- Alarm. Thisthe function is performed by cytokines, growth factors, hormone proteins. They transmit signals between organs, organisms, cells, tissues.
- Receptor. One part of the protein receptor receives an irritating signal, the other part reacts and promotes conformational changes. Thus, compounds catalyze a chemical reaction, bind intracellular messenger molecules, and 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 and reproduction of the body, and form the ability to think.
In combination with triglycerides, proteins are involved in the laying of cell membranes, with carbohydrates - in the production of secrets.
Protein synthesis is a complex process occurring 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 is composed of enzyme residues that are determined by the nucleotide sequence of the genome encoding that 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 steps.
- Transfer of information from DNA to mRNA (transcription). In prokaryotic cells, genome rewriting begins with the recognition of a specific DNA nucleotide sequence by the RNA polymerase enzyme.
- Activation of amino acids. Each "predecessor" of a protein, using the energy of ATP, binds covalently to a transfer 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.
- Binding of proteins to ribosomes (initiation). An mRNA molecule containing information about a particular protein is connected to a small particle of the ribosome and an initiating amino acid attached to the corresponding tRNA. In this case, the transport macromolecules mutually correspond to the mRNA triplet, which signals the beginning of the protein chain.
- Polypeptide chain elongation (elongation). The build-up of protein fragments occurs by the sequential addition of amino acids to the chain, which are transported to the ribosome with the help of transport RNAs. At this stage, the final structure of the protein is formed.
- Stopping the synthesis of the polypeptide chain (termination). The completion of protein construction is signaled by a special mRNA triplet, after which the polypeptide is released.from the ribosome.
- Protein folding and processing. To adopt a characteristic structure, the polypeptide spontaneously folds, forming its own spatial configuration. After synthesis on the ribosome, the protein undergoes chemical modification (processing) by enzymes, in particular, phosphorylation, hydroxylation, glycosylation, tyrosination.
Newly formed proteins contain polypeptide fragments at the end, which act as signals that direct substances to the area of influence.
Protein transformation 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.
Category of persons
Daily value in proteins, grams
|6 months to 1 year||25|
|1 to 1.5 years||36||12||48|
|1.5 – 3 years||40||13||53|
|3 – 4 years||44||19||63|
|7 – 10 years||48||32||80|
|11 - 13 years||58||38||96|
|Boys aged 14-17||56||37||93|
|Girls aged 14-17||64||42||106|
|Men (students)||68||) 45||113|
|Men engaged in heavy manual labor||66||68||134|
|Men under 70||48||32||80|
|Men over 70||45||30||75|
|Women under 70||42||28||70|
|Women over 70||39||26||65|
As It can be seen that the body's need for proteins depends on age, gender, physical condition, and load. The lack of protein in the products leads to disruption of the internal organs.
Metabolism in the human body
also 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.
- Deamination of amino acids. 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 a breakdown byproduct, ammonia. Deanimation of 90% of protein structures occurs in the liver, and in some cases in the kidneys. The exception is amino acids with a branched radical (valine, leucine, isoleucine), which are metabolized in the muscles of the skeleton.
- Formation of urea. 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, ureaenters the kidneys, from where it is excreted in the urine. The remainder of the molecule, which does not contain nitrogen, is modified into glucose, which releases energy when it breaks down.
- Interconversions between non-essential amino acid species. As a result of biochemical reactions in the liver (reductive amination, transamination of keto acids, amino acid transformations), nonessential and conditionally essential protein structures are formed, which compensate for their lack in the diet.
- Plasma protein synthesis. 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.
Protein breakdown 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 these 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.
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 muscle wasting;
- thinning of the skin fold, especially over the triceps brachii;
- dramatic weight loss;
- mental and physical fatigue;
- edema (hidden, then obvious);
- decrease in skin turgor, as a result of which it becomes dry, flabby, lethargic, wrinkled;
- deterioration in the functional state of the hair (loss, thinning, dryness);
- decreased appetite;
- poor wound healing;
- feeling constantly hungry or thirsty;
- impairment of cognitive functions (memory, attention);
- no weight gain (in children).
Be aware that signs of mild protein deficiency may be absent or hidden for a long time.
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 are more likely to suffer from respiratory diseases, pneumonia, gastroenteritis, and pathologies of the genitourinary organs. With a prolonged lack of nitrogenous compounds, a severe form of protein-energy deficiency develops, accompanied by a decrease in myocardial volume, atrophy of the subcutaneous tissue, and retraction of the intercostal spaces.
Sequelae of severe protein deficiency:
- slow heart rate;
- deterioration in the absorption of protein and other substances due to inadequate synthesis of enzymes;
- decrease in heart volume;
- egg implantation disorder;
- growth retardation (in newborns);
- functional disorders of the endocrine glands;
- hormonal failure;
- immunodeficiency states;
- exacerbation of inflammatory processes due to impaired synthesis of protective factors (interferon and lysozyme);
- decreased breathing rate.
Lack of protein in the diet has a particularly adverse effect on the child's body: growth slows down, bone formation is disturbed, mental development is delayed.
There are two forms of protein deficiency in children:
- Marasmus (dry protein deficiency). This disease is characterized by severe atrophy of muscles and subcutaneous tissue (due to protein utilization), growth retardation, and weight loss. At the same time, swelling, explicit or hidden, is absent in 95% of cases.
- 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 individualareas of the body, thinning hair. Kwashiorkor often causes vomiting, diarrhea, anorexia, and in severe cases, coma or stupor, which often ends in death.
In addition, mixed forms of protein deficiency can develop in children and adults.
Causes of protein deficiency
Possible causes of protein deficiency are:
- qualitative or quantitative nutritional imbalance (diets, starvation, protein-poor menu, poor diet);
- congenital disorders of amino acid metabolism;
- increased urinary protein loss;
- prolonged deficiency of micronutrients ;
- impaired protein synthesis due to chronic liver pathologies;
- alcoholism, drug addiction;
- severe burns, bleeding, infectious diseases;
- disorders of protein absorption in the intestine.
There are two types of protein-energy malnutrition: primary and secondary. The first disorder is due to inadequate intake of nutrients into the body, and the second is the result of functional disorders or the use of drugs that inhibit the synthesis of enzymes.
In the mild to moderate stage of protein deficiency (primary), it is important to eliminate the possible causes of the 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 because laboratory testing is required 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 protein deficiency can prevent a cure for the disease that provoked its development, inin 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 is anorexic or no cause of dysfunction is identified, anorexia drugs 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, in order to prevent protein deficiency, it is important to include protein products of plant and animal origin in the diet every day.
Excessive intake of protein-rich food 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 proteins in the body:
- exacerbation of problems with the kidneys, liver;
- worsening of appetite, respiration;
- increased nervous excitability;
- heavy menses (in women);
- difficulty losing weight;
- problems with the cardiovascular system;
- increased processes of putrefaction 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.
The 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.
Protein overdose in the human body is extremely rare. Today in a regular diet of complete proteins(amino acids) are sorely lacking.
Frequently Asked Questions
What are the pros and cons of animal and plant proteins?
The main advantage of animal protein sources is that they contain all the essential amino acids necessary for the body, mainly in concentrated form. The disadvantages of such a protein are the intake of an excess amount of a building component, which is 2-3 times higher than the daily norm. In addition, products of animal origin often contain harmful components (hormones, antibiotics, fats, cholesterol ), which cause poisoning of the body with decay products, wash out "calcium" from the bones, and 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?
- Egg, the degree of absorption reaches 95 - 100%.
- Dairy, cheese - 85 - 95%.
- Meat, fish - 80 - 92%.
- Soy - 60 - 80%.
- Grain - 50 - 80%.
- Bean - 40 - 60%.
This discrepancy is due to the fact that the digestive tract organs do not produce the enzymes necessary to break down all types of protein.
What are the recommendations for protein intake?
- Cover the body's daily requirement.
- Ensure that different combinations of protein are supplied with food.
- Do not abuse excessive amounts of protein over a long period.
- Do not eat protein-rich food at night.
- Combine plant and animal proteins. This will improve their absorption.
- It is recommended for athletes to drink a protein-rich protein shake before training to overcome high loads. After class, a gainer will help replenish nutrient reserves. Sports supplement raises the level of carbohydrates, amino acids in the body, stimulating the rapid recovery of muscle tissue.
- Animal protein should be 50% of the daily diet.
- Much more water is required to remove protein metabolism products than to break down and process other food components. To avoid dehydration, you need to drink 1.5-2 liters of non-carbonated liquid per day. To maintain water-salt balanceAthletes are advised to drink 3 liters of water.
How much protein can you digest at a time?
There is an opinion among advocates of frequent eating that no more than 30 grams of protein can be absorbed at one 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 can digest more than 200 grams of protein in one sitting. 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 the deposition of fat in the liver, increased excitability of the endocrine glands and the central nervous system, increases the processes of putrefaction, and negatively affects the functioning of the kidneys.
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 processes of 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 #2 Human Protein Needs) is essential for maintaining health and well-being throughout the day.