Proteins

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

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.

17% of the total weight of a person is made up of proteins: 10% falls on the skin, 20% – on the cartilage, bones, 50% – on the muscles. Despite the fact that the role of proteins and proteides has not been thoroughly studied today, the functioning of the nervous system, the ability to grow, reproduce the body, and the flow of metabolic processes at the cellular level are 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 a protein, based on the theory of radicals. She remained generally accepted until 1850’s. The modern name of the protein is proteins, the compound received in 1838 year. And by the end of the XIX 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”. At the beginning of the 20th century, this theory was experimentally proved 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 1960 for the first time, spatial structures of proteins at the atomic level were obtained on the basis of X-ray diffraction. At the same time, the study of this high-molecular organic compound continues to this day.

Protein structure

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

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

The “building material” for proteins is linked by a polypeptide bond, which is formed by combining one amino acid with the carboxyl of another amino acid. Short structures are usually called peptides or oligopeptides (molecular weight 3 400 – 10 000 daltons), and long, consisting of more than 50 amino acids, polypeptides. Most often, the protein chains include 100 – 400 amino acid residues, and sometimes 1000 – 1500. Proteins, due to intramolecular interactions, form specific spatial structures. 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 is a method of spatial laying of a spiral 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 coiled into a compact ellipsoidal structure. This type of protein includes enzymes, transport components of the blood, tissue proteins.

Membrane compounds are polypeptide structures that are embedded in the membrane of cellular organelles. These substances act as receptors, passing the necessary molecules and specific signals through the surface.

Today, there is a huge variety of protein structures, determined by the number of amino acid residues within them, the spatial structure and the sequence of their location.

However, for normal functioning of the body, all 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, when interacting with water 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). At the same time, the charge of a protein molecule depends on the ratio of carboxyl (–COOH), amine (NH) residues and pH of the medium. It is interesting that in the structure of animal proteins there are more dicarboxylic amino acids (glutamine and aspartic), which determines their negative “potential” in aqueous solutions.

Some substances contain a significant amount of diamino acids (histidine, lysine, arginine), which is why they behave in proteins as cationic proteins. In aqueous solutions, the substance 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, leading to a decrease in the negative potential of the protein particle. In alkali, on the contrary, 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 protein particles aggregate and precipitate. For most peptides, this value is in a weakly acidic medium. However, there are structures with a sharp predominance of alkaline properties.

At the isoelectric point, proteins are unstable in solutions, and as a result, they coagulate easily when heated. When acid or alkali is added to the precipitated protein, the molecules are recharged, after which the compound is redissolved. However, proteins retain their characteristic properties only at certain pH parameters. If somehow to destroy the bonds that hold the spatial structure of the protein, 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.

Changes in protein properties are caused by chemical and physical factors: high temperature, ultraviolet irradiation, vigorous shaking, and compounding with protein “precipitators”. As a result of denaturation, the component loses its biological activity.

Proteins give color staining during hydrolysis reactions. When the peptide solution is combined with copper sulfate and alkali, a lilac color appears (biuret reaction), when the proteins are heated in nitric acid, a yellow tint (xanthoprotein reaction) appears, when interacting with a mercury nitric solution, a 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

Organic compounds of this group, the internal organs of a person are not able to produce independently, however, they are necessary to maintain the body’s vital activity.

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

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, bones. Leucine, like valine, is involved in energy supply processes, which is especially important for maintaining endurance in the body during exhausting workouts. In addition, isoleucine is needed for the synthesis of hemoglobin.
  3. Threonine. Interferes with the fatty degeneration of the liver, is involved in protein, fat metabolism, the synthesis of collagen, elastane, creating bone tissue (enamel). Amino acid boosts immunity, susceptibility of the body to acute respiratory viral infections. Threonin is in the skeletal muscles, central nervous system, heart, supporting their work.
  4. Methionine. Improves digestion, is involved in the processing of fats, protects the body from the harmful effects of radiation, relieves signs of toxicosis during pregnancy, is used to treat rheumatoid arthritis. Amino acid is involved in the production of taurine, cysteine, glutathione, which neutralize and excrete 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 albumin, enzymes, hormones, antibodies, tissue repair and collagen formation. This amino acid is part of all proteins and is necessary to lower serum triglycerides, normal bone formation, proper absorption of calcium and thickening of the hair structure. Lysine has an antiviral effect, inhibiting the development of acute respiratory infections and herpes. It increases muscle strength, supports nitrogen metabolism, improves short-term memory, erection, female libido. Due to its positive properties, 2,6-diaminoghexanoic acid protects a healthy heart, prevents the development of atherosclerosis, osteoporosis, genital herpes. Lysine in combination with vitamin C, proline prevent the formation of lipoproteins, which cause blockage 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 an amino acid, tyrosine, which is vital for the synthesis of neurotransmitters (dopamine and norepinephrine). Due to the ability of the compound to penetrate the blood-brain barrier, it is often used to eliminate neurological diseases. In addition, the amino acid is used to combat white lesions of depigmentation on the skin (vitiligo), schizophrenia, 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 lack of the above structural units reduces athletic performance, increasing the risk of injury.

Food Sources of Essential Amino Acids

Table No. 1 “Foods rich in essential proteins”

Name
product
Amino content per 100 grams of product, grams
tryptophanthreonineIsoleucineleucine
Walnut0,170,5960,6251,17
Hazelnut0,1930,4970,5451,063
Almonds0,2140,5980,7021,488
Cashew0,2870,6880,7891,472
Fistashki0,2710,6670,8931,542
Peanut0,250,8830,9071,672
Brazilian nut0,1410,3620,5161,155
Pine nut0,1070,370,5420,991
Coconut0,0390,1210,1310,247
Sunflower seeds0,3480,9281,1391,659
Pumpkin seeds0,5760,9981,12812,419
Flax seeds0,2970,7660,8961,235
Sesame seeds0,330,730,751,5
Poppy seeds0,1840,6860,8191,321
Dried lentils0,2320,9241,1161,871
Dried mung bean0,260,7821,0081,847
Dried chickpeas0,1850,7160,8281,374
Raw green peas0,0370,2030,1950,323
Soy dried0,5911,7661,9713,309
Tofu raw0,1260,330,40,614
Tofu hard0,1980,5170,6280,963
Fried tofu0,2680,7010,8521,306
Okara0,050,0310,1590,244
Tempe0,1940,7960,881,43
Natto0,2230,8130,9311,509
Miso0,1550,4790,5080,82
Black beans0,2560,9090,9541,725
Red beans0,2790,9921,0411,882
Pink beans0,2480,8820,9251,673
Spotted beans0,2370,810,8711,558
White beans0,2770,9831,0311,865
String beans0,2230,7920,8311,502
Wheat germinated0,1150,2540,2870,507
Whole Grain Flour0,1740,3670,4430,898
Pasta0,1880,3920,570,999
Whole grain bread0,1220,2480,3140,574
Rye bread0,0960,2550,3190,579
Oats (flakes)0,1820,3820,5030,98
White rice0,0770,2360,2850,546
Brown rice0,0960,2750,3180,62
Wild rice0,1790,4690,6181,018
Buckwheat green0,1920,5060,4980,832
Fried buckwheat0,170,4480,4410,736
Millet (grain)0,1190,3530,4651,4
Barley cleaned0,1650,3370,3620,673
Boiled corn0,0230,1290,1290,348
cow milk0,040,1340,1630,299
Sheep’s milk0,0840,2680,3380,587
Curd0,1470,50,5911,116
Swiss cheese0,4011,0381,5372,959
cheddar cheese0,320,8861,5462,385
Mozzarella0,5150,9831,1351,826
eggs0,1670,5560,6411,086
Beef (filet)0,1761,071,2192,131
Pork (ham)0,2450,9410,9181,697
Chicken0,2570,9221,1251,653
Turkey0,3111,2271,4092,184
White tuna0,2971,1631,2232,156
Salmon, salmon0,2480,9691,0181,796
Trout, Mikizha0,2791,0921,1482,025
Atlantic herring0,1590,6220,6541,153

Continuation of the table number 1 “Products rich in essential proteins”

Name
product
Amino content per 100 grams of product, grams
lysinemethioninephenylalaninevaline
Walnut0,4240,2360,7110,753
Hazelnut0,420,2210,6630,701
Almonds0,580,1511,120,817
Cashew0,9280,3620,9511,094
Fistashki1,1420,3351,0541,23
Peanut0,9260,3171,3371,082
Brazilian nut0,4921,0080,630,756
Pine nut0,540,2590,5240,687
Coconut0,1470,0620,1690,202
Sunflower seeds0,9370,4941,1691,315
Pumpkin seeds1,2360,6031,7331,579
Flax seeds0,8620,370,9571,072
Sesame seeds0,650,880,940,98
Poppy seeds0,9520,5020,7581,095
Dried lentils1,8020,221,2731,281
Dried mung bean1,6640,2861,4431,237
Dried chickpeas1,2910,2531,0340,809
Raw green peas0,3170,0820,20,235
Soy dried2,7060,5472,1222,029
Tofu raw0,5320,1030,3930,408
Tofu hard0,8350,1620,6170,64
Fried tofu1,1310,220,8370,867
Okara0,2120,0410,1570,162
Tempe0,9080,1750,8930,92
Natto1,1450,2080,9411,018
Miso0,4780,1290,4860,547
Black beans1,4830,3251,1681,13
Red beans1,6180,3551,2751,233
Pink beans1,4380,3151,1331,096
Spotted beans1,3560,2591,0950,998
White beans1,6030,3511,2631,222
String beans1,2910,2831,0170,984
Wheat germinated0,2450,1160,350,361
Whole Grain Flour0,3590,2280,6820,564
Pasta0,3240,2360,7280,635
Whole grain bread0,2440,1360,4030,375
Rye bread0,2330,1390,4110,379
Oats (flakes)0,6370,2070,6650,688
White rice0,2390,1550,3530,403
Brown rice0,2860,1690,3870,44
Wild rice0,6290,4380,7210,858
Buckwheat green0,6720,1720,520,678
Fried buckwheat0,5950,1530,4630,6
Millet (grain)0,2120,2210,580,578
Barley cleaned0,3690,190,5560,486
Boiled corn0,1370,0670,150,182
cow milk0,2640,0830,1630,206
Sheep’s milk0,5130,1550,2840,448
Curd0,9340,2690,5770,748
Swiss cheese2,5850,7841,6622,139
cheddar cheese2,0720,6521,3111,663
Mozzarella0,9650,5151,0111,322
eggs0,9120,380,680,858
Beef (filet)2,2640,6981,0581,329
Pork (ham)1,8250,5510,9220,941
Chicken1,7650,5910,8991,1
Turkey2,5570,791,11,464
White tuna2,4370,7851,0361,367
Salmon, salmon2,030,6540,8631,139
Trout, Mikizha2,2870,7380,9731,283
Atlantic herring1,3030,420,5540,731

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

Semi-replaceable

Compounds belonging to this category are able to be produced by the body only if they are partially supplied with food. At the same time, each type of semi-replaceable acids performs special functions that cannot be replaced.

Consider their types.

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

A distinctive feature of semi-replaceable amino acids is the possibility of their use by the body to produce 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 what substances belong to this category.

  1. Alanine. This type of amino acid is consumed as an energy source, removes toxins from the liver, accelerates the conversion of glucose. It prevents the breakdown of muscle tissue due to the course of 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 removed from the body with urine. In addition, the substance stimulates the production of antibodies, provides the metabolism of organic acids, sugars, and boosts the immune function. Sources of alanine: dairy products, avocados, meat, poultry, eggs, fish.
  2. Glycine. Participates in building muscles, producing hormones for immunity, increases the level of creatine in the body, contributes to the conversion of glucose into energy. Glycine on 30% is part of collagen. Cellular synthesis is impossible without the participation of this compound. In fact, if tissue is damaged, without glycine, the human body cannot heal wounds. Sources of amino acids are milk, beans, cheese, fish, and meat.
  3. Glutamine. After the transformation of an organic compound into glutamic acid, it penetrates the blood-brain barrier and acts as a fuel for the brain. Amino acid removes toxins from the liver, increases GABA levels, maintains muscle tone, improves concentration and participates in the production of lymphocytes. L-glutamine preparations are usually used in bodybuilding to prevent the destruction of muscle tissue by transporting nitrogen to organs, removing toxic ammonia and increase glycogen stores. In addition, the substance is used to relieve symptoms of chronic fatigue, improve the emotional background, treat rheumatoid arthritis, ulcers, alcoholism, impotence, scleroderma. Parsley and spinach are the leaders in glutamine content.
  4. Carnitine. Binds and removes fatty acids from the body. Amino acid enhances the effects of vitamins E, C, reduces overweight, reducing 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 lipid utilization, slows down the synthesis of triglyceride molecules in the subcutaneous fat depot. After taking carnitine, the oxidation of fats in the body increases, the process of loss of adipose tissue starts, 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, and prevents the appearance of atherosclerotic plaques. Despite the fact that this amino acid does not belong to the category of irreplaceable compounds, regular intake of the substance prevents the development of heart pathologies and allows you to achieve active longevity. Remember, carnitine levels decrease with age, so older people should first of all additionally introduce a biologically active supplement in their daily diet . In addition, most of the substance is synthesized from vitamins C, B6, methionine, iron, lysine. 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. Aspargin. Needed for ammonia synthesis, proper functioning of the nervous system. 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 universal fuel for the body – adenosine triphosphate (ATP), which provides energy to 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, brain. This amino acid in the human body is synthesized independently, while its concentration in cells can be increased by including the following products in the diet: sugar cane, milk, beef, poultry.
  7. Glutamic acid. It is the most important excitatory neurotransmitter of the spinal cord, the brain. Organic compound is involved in the movement of potassium through the blood-brain barrier into the cerebrospinal fluid and plays a fundamental role in the metabolism of triglycerides. The brain is able to use glutamate as fuel. The body’s need for additional amino acid intake increases with epilepsy, depressions, 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. Serine. Regulates the amount of cortisol in muscle tissue, creates antibodies, immunoglobulins, promotes the absorption of creatine, participates in the metabolism of fats, the synthesis of serotonin. Serine supports the normal functioning of the central nervous system and the brain. The main food sources of amino acids are cauliflower, broccoli, nuts, eggs, milk, soybeans, koumiss, beef, wheat, peanuts, and 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. It is considered the standard among proteins, all other proteins are evaluated relative to it, since it has the highest digestibility. The yolk contains ovomucoid, ovomucin, lysocin, albumin, ovoglobulin, coalbumin, avidin, and albumin is the protein component. Raw chicken eggs are not recommended for people with digestive tract disorders. This is due to the fact that they contain an inhibitor of the trypsin enzyme that slows down the digestion of food and the avidin protein that attaches the vital vitamin N. The compound formed “at the exit” is not absorbed by the body and is excreted. Therefore, nutritionists insist on the use of egg protein 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 absorption rate (9 grams per hour), high amino acid composition, and helps to reduce body weight . The disadvantages of protein of eggs include their high cost.
  2. Whey Proteins in this category have the highest cleavage rate (10 – 12 grams per hour) among whole proteins. After taking products on the basis of whey, during the first hour the level of petids 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 likelihood of gas formation and digestive disorders. glutathione has a low cost relative to other types of amino acids. The main drawback of whey protein is the rapid absorption of the compound, which makes it expedient to take it before or immediately after exercise. The main source of protein is sweet whey obtained during the production of rennet cheese. There are concentrate, isolate, whey protein hydrolyzate, casein. The first of the forms obtained is not of 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 material in sports nutrition circles. Isolate is “cleaner” product, it contains 95% protein fractions. However, unscrupulous manufacturers sometimes cunning, providing as a whey protein a mixture of isolate, concentrate, hydrolyzate. Therefore, you should carefully check the composition of the additive, in which the only component should be isolate. Hydrolyzate is the most expensive type of whey protein, which is ready for immediate absorption and quickly penetrates into muscle tissue. When it enters the stomach, it turns into a clot that splits for a long time (4 – 6 grams per hour). Due to this property, the protein is part of infant formula, as it enters the body stably and evenly, while the intense flow of amino acids leads to abnormalities in the development of the baby.
  3. Vegetable. Despite the fact that proteins in such products are inferior, in combination with each other, they form a complete protein (the best combination is legumes + cereals). Bright 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 reduces cholesterol, solves the problems associated with an enlarged prostate, reduces the risk of developing malignant neoplasms in the chest. It is shown to people suffering from intolerance to dairy products. For the production of additives, soy isolate (containing 90% protein), soy concentrate (70%), soy flour (50%) are used. The rate of protein absorption is 4 grams per hour. The amino acid deficiencies include: estrogenic activity (due to this, the compound should not be taken by men in large doses, because it causes impaired reproductive function), the presence of trypsin, which slows digestion. Plants containing phytoestrogens (non-steroidal similar in structure to female hormones): flax, licorice, hops, red clover, alfalfa, red grapes. Plant proteins are also found in vegetables and fruits (cabbage, pomegranates, apples, pestilence OVDs), cereals and legumes (rice, alfalfa, lentil, flax seed, oats, wheat, soybeans, barley), beverages (beer, bourbon) .Chasto used in sports nutrition 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 the whey component, soy, casein and egg material. In addition, pea protein is rich in glutamine, lysine. The amount of BCAA in it reaches 18%. Interestingly, rice protein enhances the benefits of hypoallergenic pea protein, is used in the diet of raw food eaters, athletes, 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. At the same time, it is extremely undesirable for athletes to use protein to cover daily needs, since 3 fish protein isolate splits into amino acids more than times the 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.

Fat athletes who are prone to the formation of fat should prefer the 50-80% slower protein relatively fast. Their main spectrum of action is aimed at prolonged nourishment 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.

The intermediate position is egg white. To saturate the blood immediately after exercise and maintain a high concentration of protein after strength training, its use should be combined with serum isolate, the amino acid skor. This mixture of three proteins eliminates the disadvantages of each component, combines all the positive qualities.

Most compatible with soy protein.

Value for man

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

  1. Protective (physical, chemical, immune). Proteins protect the body from the harmful effects of viruses, toxins, bacteria, microbes, triggering the mechanism of antibody synthesis. The interaction of protective proteins with foreign substances neutralizes the biological action of harmful cells. In addition, proteins are involved in the process of coagulation of fibrinogen in the blood plasma, which contributes to the formation of a clot and clogging of the wound. Due to this, in case of damage to the body coat, the protein protects the body from blood loss.
  2. Catalytic, based on the fact that all enzymes, the so-called biological catalysts, are proteins.
  3. Transport. The main “carrier” of oxygen is hemoglobin, the blood protein. In addition, other types of amino acids in the course of reactions form compounds with vitamins, hormones, fats, providing them with transport to needy cells, internal organs, 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 human hormones (adrenaline, norepinephrine, thyroxin, glucagon, insulin, corticotropin, growth) 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. Reducing. Actin and myosin (muscle proteins) are involved in the relaxation and contraction of muscle tissue. Proteins regulate translation, splicing, gene transcription intensity, and 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 occurring in ribonucleoprotein cell particles (ribosomes). Proteins are transformed from amino acids and macromolecules “under control” of information encoded in the genes (in the cell nucleus). At the same time, each protein consists of enzyme residues, which are determined by the nucleotide sequence of the genome encoding this “building material”. Since DNA is concentrated in the cell nucleus, and protein synthesis “goes” in the cytoplasm, information from the biological memory code is transmitted to the ribosome by a special mediator, called i-RNA.

Protein biosynthesis occurs in six stages.

  1. Transfer of information from DNA to mRNA (transcription). In prokaryotic cells, “rewriting” of the genome begins with the recognition of the specific DNA nucleotide sequence by the enzyme RNA polymerase.
  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.

Newly formed proteins contain at the end polypeptide “leaders”, which perform the function of signals, directing substances to the “working” place.

Transformation of proteins is controlled by genes – operators, 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 cessation of the operon. A signal to the resumption of the system is the reaction of the substance with inductors.

Daily rate

Table № 2 “Human need for protein”

Category of personsDaily intake in proteins, grams
AnimalsVegetableTotal
6 months to 1 year25
From 1 to 1,5 years361248
1,5 – 3 years401353
3 – 4 of the year441963
5 – 6 years472572
7 – 10 years483280
11 – 13 years583896
14 boys – 17 years563793
14 girls – 17 years6442106
Pregnant women6512109
nursing mothers7248120
Men (students)6845113
Women (students)583896
Athletes
Men77-8668-94154-171
Women60-6951-77120-137
Men engaged in heavy physical labor6668134
Men up to 70 years483280
Men older than 70 years453075
Women up to 70 years422870
Women older than 70 years392665

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 – 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. Considering that protein metabolism regulates, integrates and coordinates most chemical reactions, it is important to understand the basic stages of “protein” transformations.

In the metabolism of peptides, the liver plays a key role. If the “filtering” organ ceases to participate in this process, then, in 7 days, there will be a lethal outcome.

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 deamination of amino acids, is toxic to the human body. Neutralization of toxic substances 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 with the urine. The rest of the molecule, which does not contain nitrogen, is modified into glucose, which, when decomposed, releases energy.
  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, in quantitative terms, are albumin and blood coagulation factors.
    The process of digesting proteins in the digestive tract occurs by sequential exposure of proteolytic enzymes to them to give the breakdown products the ability to be absorbed into the blood through the intestinal wall.

The splitting 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 upper segments of the small intestine, duodenum and jejunum, which receives pancreatic and intestinal juice (pH 7,2 – 8,2), containing inactive precursors of enzymes (trypsinogen, procarboxypeptidase, chemotrypsinogen, proelastase). Moreover, the intestinal mucosa produces the enzyme enteropeptidase, which activates these proteases. Proteolytic substances are also found in the mucous membrane cells of the intestinal lining, which is why hydrolysis of small peptides occurs after the final absorption.

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

Protein deficiency

Proteins are a class of high-molecular nitrogen-containing compounds, functional and structural “basis” of human life. Considering that proteins are “responsible” for the construction of cells, tissues, organs, the synthesis of hemoglobin, enzymes, peptide hormones, the normal flow of exchange reactions, their lack of a diet leads to a disruption in 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;
  • loss of skin turgor, as a result of which it becomes dry, flabby, dull, 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;
  • the deterioration of 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 a violation of the 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 of the child there is apathy, irritability, lethargy. Then, growth retardation, muscle hypotonia, fatty degeneration of the liver, and a decrease in tissue turgor are noted. Along with this, edemas appear that mask the decrease in body weight, hyperpigmentation of the skin, peeling of certain parts of the body, thinning hair. Often with kwashiorkor syndrome, vomiting, diarrhea, and anorexia occur, and in severe cases, coma or stupor, which are often fatal.

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

Reasons for the development of protein deficiency:

  • 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.

In the mild and moderate stage of the protein shortage (primary), it is important to eliminate the possible causes of the development of pathology. To do this, increase the daily protein intake (in proportion to the optimal body weight), appoint multivitamin complexes. In the absence of teeth or loss of appetite, additionally use liquid nutritional mixtures for probe or independent feeding. If the “protein deficiency” is complicated by diarrhea, then it is preferable for patients to be given yogurt preparations. In no case is it recommended to use dairy products, due to the inability of the body to process lactose.

Severe forms of secondary failure require inpatient treatment, since laboratory research is necessary to identify the disorder. To clarify the cause of the pathology, the level of soluble receptor for interleukin-2 in blood or C-reactive protein is measured. At the same time, tests for plasma albumin, skin antigens, the total number of lymphocytes and CD4 + T-lymphocytes will help confirm the history and determine the degree of functional dysfunction.

The main priorities of treatment are the observance of a controlled diet, correction of water and electrolyte balance, elimination of infectious pathologies, saturation of the body with nutrients. Given that the secondary lack of protein, can prevent the cure of the disease, which provoked its development, in some cases, prescribe parenteral or tube feeding 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 is not identified, additionally use drugs that increase appetite. To increase lean body mass, anabolic steroids can be used (under the supervision of a physician). Restoration of protein balance in adults occurs slowly over the course of 6 – 9 months. In children, the full recovery period takes 3 – 4 month.

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. Remember, an overdose of protein in the diet is no less dangerous deficiency!

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 dropping overweight;
  • problems with the cardiovascular system;
  • increased rotting in the intestines.

To determine the violation of protein metabolism can be using nitrogen balance. If the amount of produced and excreted nitrogen is the same value, it is considered that the person has a positive balance. Negative equilibrium indicates a lack of intake or poor absorption of protein, which leads to the burning of the body’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 does not harm human health. In this case, an excess of amino acids is used as an energy source. However, in the absence of physical exertion, for most people, protein intake in excess of 1,7 grams per 1 kilogram of weight contributes to the conversion of excess protein into nitrogenous compounds (urea), glucose, which must remove the kidneys. Excessive amount of the building component contributes to the formation of an acidic reaction of the body, increasing calcium loss. In addition, the composition of animal protein often includes 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.

Frequently asked Questions

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 harmful components that go “into the load” with animal protein. However, vegetable proteins are not free from deficiencies. Most products (except soy) are combined with fats (in seeds), contain an incomplete set of essential amino acids.

What 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 body’s daily need for an organic compound.
  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 food rich in proteins at night.
  5. Combine proteins of plant, 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. 50% of the daily diet should be animal proteins.
  8. For the removal of protein metabolism products requires much more water than for splitting and processing other components of the food. To avoid dehydration of the body in a day you need to drink 2 liters of non-carbonated liquid. To maintain water-salt balance, athletes are advised to use 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 is able to overcome more than 200 grams of protein in one sitting. At the same time, the share of protein will go to participate in anabolic processes or the SMP and will be stored as glycogen. The main thing to remember is, the more protein goes into the body, the longer it will digest it, but the whole 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, transport, energy and metabolic functions. Compounds are involved in the absorption of minerals, vitamins, fats, carbohydrates, increase immunity and serve as a building material for muscle fibers.

The daily intake of protein in sufficient quantities (see Table No. 2 “Human Requirement for Proteins”) is the key to maintaining good health during the day.

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