Proteins - structure, functions, synthesis
Proteins play huge role in organism.
They therefore were called proteins (from Greek "protos" - the first) that they are basis of structure of each body, each cage.
Actually and life, by F. Engels's definition, is way of existence of proteinaceous bodies which major moment is the constant metabolism with the external nature surrounding them. With the termination of this metabolism also life stops that leads to protein decomposition.
As life - the way of existence of proteinaceous bodies, so, is not present protein - there is no life. In organism of squirrel carry out the most different tasks. We have not studied some functions of proteins yet or even about them we do not suspect. But also what is already known impresses.
Protein was meant as colourless semi-fluid component of egg in the beginning, then this word became collective for a number of substances which have much in common in properties, are present at each living cell and form the main mass of protoplasm.
Structure of proteins
There are millions of different proteins, but all of them are constructed of the "bricks" belonging to one class of substances - to amino acids. In total nowadays there are about 180 amino acids. According to scientists, amino acids exist on our planet more than 3 billion years that confirm researches of fossil microorganisms.
Amino acids are organic compounds which physicochemical behavior and various reactions are explained by simultaneous presence at molecule of the bases of amino group of NH2 and acids of carboxyl group COOH. All amino acids are constructed according to one scheme.
According to the simplified standard scheme the main 20 amino acids share on replaceable and irreplaceable depending on whether they can be synthesized (to be formed) in human body or not. Plants and some microorganisms can make all amino acids necessary to them for synthesis of proteins of cages. Animals are capable to synthesize only 10 proteinogenous amino acids. The others 10 that cannot be received by means of biosynthesis, have to come constantly to organism in the form of food proteins. Absence them in organism and even more or less long deficit is conducted to the menacing phenomena: to growth inhibition, negative nitric balance, disorder of biosynthesis of proteins.
The amino-acid composition of this or that protein determines its value which is limited by the scantiest of irreplaceable amino acids. When it is settled, all other food goes for emission.
For animals proteins of milk are considered as the most valuable. All other proteins are also compared to them usually. For orientation we will provide the table of content of irreplaceable amino acids in milk and some other products as a percentage of contents them in protein of cow's milk.
|Name of irreplaceable amino acid||Contents in 100 g of protein of cow's milk,||Contents in relation to its content in protein of cow's milk, %|
One of the main criteria of sufficiency of proteinaceous food - achievement of nitrogenous balance. By this principle in 1982 calculation of norm of protein has been made. Essence of this method in establishment of compliance between loss by nitrogen organism with allocations and receipt it with food. If amount of the consumed nitrogen to equally total quantity allocated, then the nitrogenous balance is equal to zero and the organism is in condition of nitrogenous balance. If the amount of the consumed protein exceeds quantity removed, then nitrogenous balance positive if it is removed more, than is entered, then nitrogenous balance negative.
At elimination from food at least of one irreplaceable amino acid necessary for maintenance of nitrogenous balance, the organism will begin to lose nitrogen of proteinaceous reserves of body. At proteinaceous exhaustion decrease (and very quickly) proteinaceous reserves of organism, there is shift of water exchange, all other exchange processes and the correct functioning of bodies are broken.
Proteins of organism not only make its basis, they are catalysts and the centers of dynamic balance of the vital phenomena; they represent themselves also proteinaceous reserves of organism to which number proteins of liver, plasma and other fabrics belong. However proteinaceous reserves are very insignificant and their use is extremely undesirable as actually it is not about excess of proteins, and about some short period of use of fabric proteins for maintenance of integrity of the major proteinaceous structures of organism.
By drawing up food allowance it is necessary to know that proteins can effectively carry out the functions in organism only if all necessary components of food are present at it in enough. If, let us assume, there are no carbohydrates and fats, then the organism is forced to use amino acids of proteins as power source in this connection squirrels "will distract" from the main function: education and recovery of body tissues. Absence in food of some vitamins which are active components of proteinaceous catalysts of intermediate exchange also does not promote performance by proteins of the main objective at all. Therefore the biological assessment of proteins of food also should be made at full accounting of their interconnection with other components of food.
However, that protein became effective construction material in organism, irreplaceable amino acids have to possess one feature. They should be released at digestion with the speed providing replenishment of their stocks in fabrics. So, as the distinction reason in nutritional value of proteins this quality - distinction can serve in the speed of release of separate amino acids in intestines. In this regard data on influence on nutritional value and speed of digestion of any proteins of mechanical, chemical and culinary processing of foodstuff are interesting.
Scientists have established, for example, that long heating of acid products leads to lowering of otshcheplyaemost of important amino acids: lysine and tryptophane, and also arginine. Noticeable decrease in nutritional value of protein of grain comes in the course of receiving from it, for example, flakes, and the pastries and drying of foodstuff reduce availability to the organism which is available in are mute lysine.
Not only processing of products exerts impact on the biological value of proteins. Proteins of the same products have different biological value, have been differently processed at preservation. It depends and on conditions and periods of storage, availability of toxic substances which nowadays, in the conditions of general, global environmental pollution, quite often appear in food. Besides, the food contains unequal quantity of other components: vitamins, provitamins, mineral substances, fabric hormones and pro-hormones, and they can also influence assimilation and use of proteins organism. Recently it is established that nutritional value of proteins depends not only on ratio in them replaceable and irreplaceable amino acids, but also from contents of strepogenin in them - substance of polypeptide character.
The minimum quantity of protein sufficient for achievement of nitrogenous balance, that is for covering of need of organism for protein, depends on its quality. According to definition of the American scientist, founder of the doctrine about proteins G. Thomas the biological value of proteins of food is characterized by amount of their nitrogen which is late in body of animal. So, for achievement of nitrogenous balance 30-31 grams of protein of milk, but already suffice 76 grams of protein of wheat and 102 grams of protein of corn. A.A. Pokrovsky considered that at the normal content of proteins in food of the population nitrogenous balance is reached when using proteins of animal and plant origin in the ratio 1:1. And here for athletes, pregnant women and the feeding women, children the quota of proteins of animal origin has to be increased, that is the ratio it has to look so: 60 percent of animal and 40 percent of vegetable protein. For the normal growth and development in diet there have to be at optimum quantities first of all 10 irreplaceable amino acids. At the same time it must be kept in mind that one some amino acid can be irreplaceable for growth, but replaceable for implementation of other functions of live organism. Besides, the set of irreplaceable amino acids and their optimum ratio in diet can change depending on physiological condition of organism.
Throughout long evolutionary development in human body adaptive mechanisms which allow to reach nitrogenous balance at very different amounts of the proteins arriving with food were developed. It is visible at least from comparison of diet of the separate people. Considerable dominance in food of proteins of animal origin over vegetable, and at others quota of animal protein very low is characteristic of some nations. Throughout centuries they have adapted to the food poor in animal protein.
Scientists have established that at the increased amount of protein in food two effects can take place. The first: with increase in consumption of protein also nitrogen conclusion from organism increases. The second: the part of the protein coming to organism goes to stock, on creation of functional reserves of bodies and fabrics, increasing organism resilience.
But here paradox: even if the food contains sufficient or excess amount of full-fledged proteins, but there are no carbohydrates and fats, the organism begins to lose nitrogen. And if, say, the amount of carbohydrates in food sharply exceeds norm, the need of organism for protein can be considerably reduced. This effect of carbohydrates preserving protein cannot be understood and interpreted vulgarly: to save proteins at the expense of sugar... Food has to be balanced on all components, and the hobby for carbohydrates most often is the reason of excess weight and obesity.
The body of the adult weighing 70 kilograms contains 15-17 kilograms of proteins, and in only 70 years of life he eats them about 2,5 tons. Process of updating of protein of different human organs is not identical. For example, half of proteins of liver and plasma of blood is replaced within 10 days, and in muscles and skin this process proceeds 158 days. The biochemical basis of cages is made by proteinaceous molecules therefore the term of life depends first of all on the term of life of these molecules. Life expectancy of cages of separate bodies is different. In particular, red blood cells (erythrocytes) live about 120 days, so 1/120 part them, that is 20-25 grams daily are replaced. Other cages are even less long-lasting. For example, white blood cells (leukocytes) live in blood from several hours to 7 days, the same term of life and at cells of mucous membranes of stomach and intestines.
But even irrespective of isolation of life of cages their components, first of all proteinaceous molecules are subject to continuous updating. Many squirrels cannot long carry out the specific functions and quickly "grow old", that is lose special characteristics and qualities inherent in them. Therefore daily with food protein which requirement makes about 1,5 grams on kilogram of body weight has to come to organism (the adult man means). It means that the man with the body weight of 70 kilograms has to consume daily 105 grams of protein (50 percent of animal and 50 percent of vegetable). Children and teenagers during intensive growth, to pregnant women and nursing mothers, and also many patients, especially during recovery, need food rich with protein - to 2 grams of protein on kilogram of body weight. And all this because proteins are carriers of the most important functions of human body: structural, motive, protective, enzymatic and some other.
By the way, on "the construction purposes" also some part of fats (lipids) which in complex with protein are source of formation of cellular membranes, enzymes and other connections is used. The separate carbohydrates forming glikoproteidny complexes with protein also participate in such unusual "construction".
In addition to so-called structural proteins, enzymes - biological catalysts, important accelerators of biochemical reactions in organism belong to albumens. At the same time some reactions thanks to enzymes accelerate by 10-100 times. Special enzymes are emitted in digestive tract of the person, they are capable to split the proteins coming to organism with food of the person to separate amino acids.
Enzymes are present at each cell of human body and promote various chemical reactions of exchange. Pepsin, trypsin, chymotrypsin, peptidases, amylase, lipase are especially important among them. Noting outstanding role of enzymes in life activity of the person, I.P. Pavlov called them life activators.
Proteins are also some hormones which also regulate exchange processes in organism. For what they are necessary? Well, say, in order that the proteinaceous exchange went properly. Intake of protein in organism was slowed down, hormones help to use protein from fabric reserves. It is done, in particular, by steroid hormones of bark of adrenal glands. Insulin, regulating exchange of carbohydrates, also renders though indirect, but deep influence on proteinaceous exchange.
Thus, in organism there are two classes of the substances influencing the speed of chemical reactions - hormones and enzymes which are in very difficult interrelation. For example, hormone thyroxine strengthens function of number of enzymes, and also action of amino-acid oxidases in liver and enzymatic synthesis of amino acids from ketonic acids and ammonium salts. Hormones influence growth as the general, and separate fabrics and bodies.
As we see, protein plays important role in life activity of organism therefore those who it is too free unreasonably arrive varies amount of protein in the diet, especially towards its reduction or even refusal of one of them - plant or animal origin. Proteinaceous starvation leads to heavy frustration. The children's organism is especially sensitive to deficit of protein. At the child in this case there can come the delay, and in hard cases and complete cessation of growth. It becomes sluggish, strongly grows thin, heavy hypostases, diarrhea, inflammation of integuments can develop; all this is followed by anemia, there comes heavy disorder of functions of liver and pancreas. The organism of the child weakened by proteinaceous deficit ceases to resist different diseases, in particular infectious. And it is not the full list of possible serious consequences of proteinaceous insufficiency in the child's diet.
What the hostess needs to know about protein at catering services in family?
For full digestion of protein of food contained in amino acids have to be mute are balanced. Proteins in products of animal origin differ in such balance. On the first place put usually milk. The liter of whole milk contains daily need of human body for all amino acids. Also products rich with protein - different dairy products, meat, fish differ in the high biological value, that is balance of amino acids, easy digestibility and good comprehensibility. Recently in our diet the increasing place is taken by such product the containing protein - meat of squid which protein differs in so high biological value, as milk: in it is mute all amino acids necessary for the person contain. At the same time the amino-acid composition of this protein is almost adequate to amino-acid composition of protein of the person.
The vegetable proteins having insufficiently balanced amino-acid structure are less valuable in a qualitative sense. Meanwhile residents of our country satisfy nearly 1/3 needs of organism for protein at the expense of protein of bread which contains not enough lysine, one of the main irreplaceable amino acids. Deficit of lysine and threonine have, by the way, almost all grain, except buckwheat. Proteins in products of plant origin difficult are digested as are put into covers from cellulose of other substances interfering action on them digestive enzymes. In this plan especially trudnoperevarivayema of squirrel bean, mushrooms, nuts, grain from whole grains. That is why from proteins of animal products in intestines more than 90 percent of amino acids, and from vegetable - only 60-80 percent are soaked up.
The hostess should know that razvarivaniye, crushing, wiping improves digestion and digestion of proteins. At the same time excess heating of vegetable and especially animal protein negatively influences amino acids. Let's tell, the biological value of milk protein of casein when heating to 200 degrees falls for 50 percent. At strong and long heating of products rich with carbohydrates in them the quantity of lysine, available to assimilation, decreases. Therefore if you cook porridge, it is rational to wet previously grain - it will reduce time of cooking and will increase nutritional value of the final product.
To improve total balance of amino acids, it is necessary to combine animal and vegetable products: dairy products - with bread, grain, macaroni, flour products - with cottage cheese, fish, meat, potatoes and vegetables - with meat and fish.
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