Determination of the amino acid composition of proteins can be carried out by various methods: chemical, chromatographic, microbiological and isotope. Chromatographic methods are more often used.
Paper chromatography. Paper chromatography is used to identify the components of a mixture of amino acids with di- and tri-peptides obtained by partial hydrolysis of proteins and polypeptides.
Hydrolysis can be carried out by acid, alkaline or enzymatic methods. The acid method is used more often (6 N HCl, 8 N H 2 SO 4). Hydrolysis is carried out by heating, sometimes at elevated pressure. Indicators of the end of hydrolysis can be: cessation of the growth of carboxyl or amine groups in the hydrolyzate, or a negative biuret reaction. The excess hydrolyzing reagent is removed: sulfuric acid is precipitated with Ca(OH) 2, hydrochloric acid is distilled off in vacuum, and the remaining acid is precipitated with silver nitrate.
The components of the hydrolyzate are distributed between water adsorbed on the cellulose, which is the stationary phase, and an organic solvent, the mobile phase, which moves up or down along the sheet. A mixture of butanol-acetic acid-water (4:1:5) is used as the mobile phase. More lipophilic amino acids are more strongly attracted to the organic solvent, while more hydrophilic ones show a greater tendency to bind to the stationary phase. Homologous compounds that differ by even one methylene unit move at different speeds and can be easily separated. At the end of the chromatography, the paper is dried and treated with a developer (0.5% solution of ninhydrin in a mixture of acetone-glacial acetic acid-water) and heated for several minutes. Amino acids appear as colored spots. Mobility is a constant value characteristic of each compound and increases with increasing molecular weight. For straight-chain amino acids, the mobility value is slightly higher than for the corresponding isomers. The introduction of polar groups into the molecule reduces the mobility of the compound. Amino acids with bulky nonpolar side chains (leucine, isoleucine, phenylalanine, tryptophan, etc.) move faster than amino acids with shorter nonpolar side chains (proline, alanine, glycine) or with polar side chains (threonine, arginine, cysteine, histidine, lysine). This is due to the greater solubility of polar molecules in the hydrophilic stationary phase and of non-polar molecules in organic solvents.
Paper chromatography can be used to quantify amino acid content. Each spot is excised and eluted with a suitable solvent; then a quantitative colorimetric (ninhydrin) assay is performed. In another embodiment, the paper is sprayed with ninhydrin and the color intensity of the spot is measured using a photometer in reflected or transmitted light. In a semiquantitative assessment, the amino acid content is assessed by the area of spots on the chromatogram, which are proportional to the concentrations of amino acids in the mixture being separated.
Thin layer chromatography. Thin layer chromatography can also be used to separate and determine amino acids. TLC, as is known, exists in two versions. Partition TLC is similar to partition TLC on paper, and adsorption TLC is based on completely different principles.
When performing RTLC on cellulose powder or other relatively inert carriers, the same solvent systems and the same developing reagents can be used as in paper chromatography.
Separation by ATLC is determined by the ability of a solvent (this solvent is not necessarily a binary or more complex mixture) to elute the components of the sample from the site of its adsorption on the activated sorbent. For example, on heated silica gel. ATLC is useful for the separation of non-polar compounds such as lipids, but not for the separation of amino acids and most peptides. To separate amino acids, RTLC is used, which allows you to quickly separate and determine 22 amino acids of protein hydrolysates.
Amino acids in protein hydrolyzate can also be determined by gas chromatography, but before chromatographic analysis, amino acids are usually converted into volatile compounds.
Interaction with ninhydrin. The corresponding aldehydes are formed.
Thus, a mixture of aldehydes is obtained and analyzed. This is the simplest case, suitable only for some amino acids.
Amino acids are converted into volatile esters (alkyl esters, methyl esters of hydroxy acids, methyl esters of chlorinated acids, etc.).
The choice of derivatives depends on the mixture of amino acids being studied.
Ion exchange chromatography. Currently, the amino acid composition of food products is determined exclusively using automatic ion exchange chromatography.
| Ion exchange chromatography is based on the reversible stoichiometric exchange of ions in solution with ions included in the ion exchanger (cation exchanger, anion exchanger) and on the different ability of the separated ions to ion exchange with fixed sorbent ions formed as a result of the dissociation of ionogenic groups. For organic ions, the electrostatic interaction with fixed charges of the ion exchanger is superimposed by the hydrophobic interaction of the organic part of the ion with the ion exchanger matrix. To reduce its contribution to the retention of organic ions and achieve optimal selectivity of their separation, an organic component (1–25% methanol, isopropanol, acetonitrile) is added to the aqueous eluent. |
The Moore and Stein method uses short and long columns filled with sulfonated polystyrene resin in Na + form. When an acid hydrolyzate at pH = 2 is applied to the column, amino acids bind through cation exchange with sodium ions. The column is then eluted with sodium citrate solution at preprogrammed pH and temperature values. A short column is eluted with one buffer, a long column with two. The eluate is treated with ninhydrin, measuring the color intensity using a flow colorimeter. The data is automatically recorded on a chart recorder and can be transferred to a computer to calculate the area under the peak.
High-voltage electrophoresis on inert carriers. In biochemistry, the separation of amino acids, polypeptides and other ampholytes (molecules whose total charge depends on the pH of the environment) under the influence of an applied constant electric field has found wide application. This is a method of high-voltage electrophoresis on inert carriers. When separating amino acids, strips of paper or thin layers of cellulose powder are most often used as inert carriers. Separation is carried out for 0.5–2 hours at a voltage of 2000–5000 V, depending on the total charges of the ampholytes and their molecular weights. Among molecules carrying the same charge, lighter ones migrate faster. But a more important parameter during separation is the total charge. The method is used to separate amino acids, low molecular weight peptides, some proteins, and nucleotides. The sample is placed on the carrier, moistened with a buffer at the appropriate pH and connected to the buffer reservoir with a strip of filter paper. The paper is covered with a glass plate or immersed in a hydrocarbon solvent for cooling. In an electric field, molecules that carry a negative charge at a given pH migrate to the anode, and those that carry a positive charge migrate to the cathode. Next, the dried electropherogram is “developed” with ninhydrin (when working with amino acids, peptides) or measuring absorption in UV light (when working with nucleotides).
The choice of pH is determined by the pK values of the dissociating groups included in the molecules of the mixture. At pH 6.4, glutamate and aspartate carry a –1 charge and move toward the anode; their separation is carried out due to the difference in molecular weight. Lysine, arginine and histidine move in the opposite direction, and all other amino acids that make up the protein remain near the site of application. When separating peptides resulting from enzymatic digestion, decreasing the pH to 3.5 increases the charge of the cationic groups and provides better separation.
| Amino acids carry at least two weakly ionized groups: -COOH and -NH 3 +. In solution, these groups are in two forms, charged and uncharged, between which proton equilibrium is maintained: R-COOH « R-COO – + H + R-NH 3 + « R-NH 2 + H + (conjugate acids and bases) R -COOH and R-NH 3 + are weak acids, but the first is several orders of magnitude stronger. Therefore, most often (blood plasma, intercellular fluid pH 7.1–7.4) carboxyl groups are in the form of carboxylate ions, amino groups are protonated. Amino acids do not exist in molecular (non-dissociated) form at any pH. The approximate pK values of an a-amino acid and the a-amino group in an a-amino acid are 2 and 10, respectively. The total (total) charge (algebraic sum of all positive and negative charges) of an amino acid depends on pH, i.e. on the concentration of protons in the solution. The charge of an amino acid can be changed by varying the pH. This facilitates the physical separation of amino acids, peptides and proteins. The pH value at which the total charge of an amino acid is zero and therefore does not move in a constant electric field is called the isoelectric point (pI). The isoelectric point is located midway between the nearest pK values of dissociating groups. |
Methods of paper, thin-layer chromatography, microbiological, gas chromatography and a number of others are currently practically not used due to poor reproducibility and long duration. Modern chromatographs make it possible to determine the amino acid composition of a mixture containing only 10 –7 –10 –9 mol of each component with a reproducibility of up to 5% in 2–4 hours.
Analysis of amino acid composition includes complete hydrolysis of the protein or peptide under study and quantitative determination of all amino acids in the hydrolyzate. Since peptide bonds are stable at neutral pH, acid or alkaline catalysis is used. Enzymatic catalysis is less suitable for complete hydrolysis. Complete hydrolysis of a protein into its constituent amino acids is inevitably accompanied by a partial loss of some amino acid residues. For hydrolysis, 6N is usually used. aqueous solution of hydrochloric acid (110ºС), in a evacuated ampoule. Quantitative determination of amino acids in the hydrolyzate is carried out using an amino acid analyzer. In most of these analyzers, a mixture of amino acids is separated on sulfonic cation exchangers, and detection is carried out spectrophotometrically by reaction with ninhydrin or fluorimetrically with O-phthalic dialdehyde.
However, data on the amino acid composition of similar products obtained in different laboratories for individual amino acids sometimes differ by up to 50%.
These differences are due not only to varietal, species or technological differences, but mainly to the conditions for hydrolysis of the food product. With standard acid hydrolysis (6 N HСl, 110–120ºС, 22–24 hours), some amino acids are partially destroyed, including threonine, serine (by 10–15% and the more, the longer the hydrolysis is carried out) and especially methionine ( 30–60%) and cystine 56–60%, as well as almost complete destruction of tryptophan and cysteine. This process is enhanced in the presence of large amounts of carbohydrates in the product. For the quantitative determination of methionine and cystine, it is recommended to carry out their preliminary oxidation with performic acid. In this case, cystine is converted into cysteic acid, and methionine into methionine sulfone, which are very stable during subsequent acid hydrolysis.
Cystine Cysteine acid
A difficult task in amino acid analysis is the determination of tryptophan. As already mentioned, during acid hydrolysis it is almost completely destroyed (up to 90%). Therefore, to determine tryptophan, one of the variants of alkaline hydrolysis of 2 N is carried out. NaOH, 100ºС, 16–18 hours in the presence of 5% tin chloride or 2 N. barium hydroxide, in which it is destroyed slightly (up to 10%). Minimal degradation occurs in the presence of thioglycolic acid and pre-hydrolyzed starch. (During alkaline hydrolysis, serine, threonine, arginine and cysteine are destroyed). After neutralization with a mixture of citric and hydrochloric acids, the hydrolyzate is immediately analyzed (to avoid gelation) on an amino acid analyzer. As for the numerous chemical methods for determining tryptophan, they are, as a rule, poorly reproducible in food products and therefore their use is not recommended.
For meat products, an additional essential amino acid is hydroxyproline, which characterizes the amount of connective tissue proteins in meat. It can be determined by ion exchange chromatography using automatic analyzers or by a chemical colorimetric method. The method is based on neutralization of the acid hydrolyzate to pH 6.0, subsequent oxidation of hydroxyproline using a 1.4% solution of chloramine T (or chloramine B) in a mixture of propyl alcohol and buffer, colorimetric determination at 533 nm of the oxidation products of hydroxyproline after reaction with 10% - a solution of para-dimethylaminobenzaldehyde in a mixture of perchloric acid and propyl alcohol (1:2).
Due to the fact that tyrosine, phenylalanine and proline can be partially oxidized in the presence of oxygen, standard acid hydrolysis is recommended to be carried out in a nitrogen atmosphere. A number of amino acids, including leucine, isoleucine and valine, require longer acid hydrolysis for their complete isolation from proteins - up to 72 hours. In biochemistry, when analyzing proteins, parallel samples are hydrolyzed for 24, 48, 72 and 96 hours.
To accurately quantify all amino acids, it is necessary to carry out 5 different hydrolysis, which greatly lengthens the determination. Usually, 1–2 hydrolysis is carried out (standard with hydrochloric acid and with preliminary oxidation with performic acid).
To avoid loss of amino acids, removal of excess acid during acid hydrolysis should be carried out immediately by repeated evaporation in a vacuum desiccator with the addition of distilled water.
When the analyzer operates correctly, ion exchange columns operate for quite a long time without replacing the resin. However, if the samples contain significant amounts of dyes and lipids, the column quickly becomes clogged and multiple regenerations, sometimes involving repacking of the column, are required to restore its separation capabilities. Therefore, for products containing more than 5% fat, it is recommended to first remove lipids by extraction. Table 2.3 shows the conditions for sample preparation of main food products when analyzing the amino acid composition.
Table 2.3. – Conditions for preparing food samples for analysis
| Product | Lipid removal method | Weight ratio of protein: HCl (6M) |
| Protein concentrates (isolates) | Not required | 1:200 |
| Meat, fish, canned meat and fish, offal) | Extraction with 10 times diethyl ether 3–4 times or 10 times ethanol-chloroform (1:2) 2 times | 1:250 |
| Milk and dairy products | Extraction with a 10-fold amount of the sample using a mixture of ethanol-chloroform (1:2) 2 times | 1:1000 |
| Grain and grain products | Not required | 1:1000 |
| Plant products | Not required | 1:500 |
| Meat-vegetable and fish-vegetable products | Extraction with 10 times the amount of diethyl ether 3-4 times; a mixture of ethanol-chloroform (1:2) 10 times the amount weighed 2 times | 1:1000 |
| Egg, egg products | Extraction with a mixture of ethanol-chloroform (1:2), 10 times the amount weighed 2 times | 1:200 |
Control questions:
1. Define the concept of “proteins”.
2. What groups are proteins divided into according to their functions in the body?
3. What is the role of proteins in human nutrition?
6. What essential amino acids do you know and which amino acids can become essential?
7. How is the total nitrogen content in food products determined?
8. How is the amino acid composition of proteins determined?
9. What methods for determining amino acids do you know?
§ 2.4. Carbohydrates
Carbohydrates are widely present in plants and animals, where they perform both structural and metabolic functions. In plants, during the process of photosynthesis, glucose is synthesized from carbon dioxide and water, which is then stored in the form of starch or converted into cellulose, the structural basis of plants. Animals are able to synthesize a number of carbohydrates from fats and proteins, but most carbohydrates come from plant foods.
Contents Introduction 1. Main components of milk 2. Methods of amino acid analysis 1. Chromatographic method of analysis 2. Spectrophotometric method of analysis 3. Titrometric method of analysis 4. Electrochemical method of analysis 3. Methods for determining amino acid composition 1. Determination of amino acids by thin layer chromatography 3.2. Determination of amino acids by the spectrophotometric method 4. Review of abstract journals List of used literature Introduction The problem of nutrition is one of the most important social problems.
Human life, health and work are impossible without nutritious food. According to the theory of balanced nutrition, a person’s diet should contain not only proteins, fats and carbohydrates in the required quantities, but also substances such as essential amino acids, vitamins, and minerals in certain proportions beneficial to humans.
In organizing proper nutrition, a primary role is given to dairy products. This fully applies to milk, the nutritional value of which is due to the high concentration of milk protein and fat in it, the presence of essential amino acids, calcium and phosphorus salts, which are so necessary for the normal development of the human body. Easy digestibility is one of the most important properties of milk as a food product. Moreover, milk stimulates the absorption of nutrients from other foods.
Milk adds variety to the diet, improves the taste of other products, and has therapeutic and prophylactic properties. Milk contains more than 120 different components, including 20 amino acids, 64 fatty acids, 40 minerals, 15 vitamins, dozens of enzymes, etc. The energy value of 1 liter of raw milk is 2797 kJ. One liter of milk satisfies the daily need of an adult for fat, calcium, phosphorus, 53% for protein, 35% for vitamins A, C and thiamine, and 26% for energy. The main goal of this course work is to identify the amino acid composition of milk. 1.
Main components of milk
From a physicochemical point of view, milk is a complex polydisperse... 5.1). The largest specific gravity in milk is water (more than 85%, the rest... The dry residue includes all the nutrients of milk. It determines the yield of finished products in the production of dairy products...
Chromatographic method of analysis
One of the most promising methods is the highly effective method... But the advantages of the method significantly outweigh its disadvantages. In addition, it can be used to complete chemical analysis.... On modern gas chromatographic capillary columns in one ex... The method is characterized by high sensitivity and allows quantitative...
Titrometric method of analysis
Titrometric method of analysis. Of the titrimetric methods for quantitative determination, the widest... Titration can be carried out with an indicator (crystal violet... However, this method has a number of significant disadvantages: the use... For the quantitative analysis of individual amino acids, met...
Electrochemical method of analysis
In recent decades, electrochemicals have become increasingly widespread... 3.. under optimized conditions, they make it possible to determine only individual am... Thus, a method has been developed for the polarographic determination of tryptophan, a basic... Electrochemical method of analysis.
Methods for determining amino acid composition
Methods for determining amino acid composition 3.1.
Determination of amino acids by thin layer chromatography
84 g of citric acid monohydrate are dissolved in 1 liter of distilled water... 3.2.. After 10 minutes, the film is placed in a CG chamber with a nitrate buffer (buffer... Methodology: 2 (10) µl of p hydrolyzate is applied to the starting line of the plate... Drops samples and standard amino acids are applied to the starting line on the...
Determination of amino acids by spectrophotometric method
Amino acids, primary amines, polypeptides and peptones when heated with... 0.2 - 3% solution of ninhydrin are prepared in different solvents (isobu... 2007. volume 2. Tsvetkova N.D.
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The following stages can be distinguished in elucidating the primary structure of proteins and peptides:
1. Isolation of protein in its pure form and determination of its molecular weight
2. Determination of amino acid composition
3. Determination of N-terminal amino acid
4. Determination of the C-terminal amino acid
5. Determination of amino acid sequence
Isolation of protein in its pure form. Typically, the starting material contains many different proteins. In this regard, the problem arises of isolating the protein of interest in its pure form from this mixture. When purifying proteins, methods are used that are based on the difference:
1. Surface charge of proteins
2. Molecular size of proteins (depending on their molecular weight)
3. Biological activity due to binding to substrates or inhibitors
Separation of proteins based on differences in surface charge. The total surface electrical charge of a protein at a given pH value can be negative, neutral or positive. To separate proteins with different charges, as was the case with amino acids, the method of ion exchange chromatography (see above) can be used. The protein concentration in test tubes with the eluate is determined using a spectrophotometer based on the intensity of ultraviolet light absorption and a graphical dependence is plotted on the volume of liquid flowing out of the chromatographic column.
Separation of proteins by molecular weight. If you imagine protein molecules in the form of balls of various sizes, the size of which depends on their molecular weight, then it turns out that larger balls will have a larger molecular mass or molecular size. This means that proteins can be separated like particles in a sieve - a molecular sieve formed by a gel. This method is often called gel filtration or size exclusion chromatography. Below is an illustration of how gel filtration can separate a mixture of proteins of different sizes (Fig. 1.12).
The chromatographic column is filled with a swollen gel. The gel particles are made from cross-linked polysaccharide material and contain a large number of micropores. The size of the micropores is selected in such a way that the smaller molecules being separated penetrate into them, while the larger ones cannot do this. The mixture of proteins to be separated is applied to the top of the column and eluted with a buffer solution. Large molecules carried away by the flow of downward liquid, unable to penetrate the pores of the gel particles, will move faster. Smaller molecules penetrate the pores and remain there. If you collect the solution flowing from the column in equal portions into test tubes, it will turn out that earlier portions of the flowing liquid will contain proteins of large sizes, and later portions will contain proteins of smaller sizes. By selecting the pore size, the separation of a wide variety of protein mixtures can be achieved.
Fig.1.12. Schematic illustration of protein separation by gel filtration
If we take into account that the size of a molecule depends on the molecular weight, it turns out that by separating proteins by gel filtration, it is simultaneously possible to determine its molecular weight.
Fig.1.13. Graph of the dependence of the molecular weight of proteins on the volume of their output from the chromatographic column during gel filtration
The volume of eluate flowing from the column is inversely proportional to the logarithm of the molecular weight of the protein. Thus, it is enough to know the volume of liquid in which the protein of interest came out of the column so that, using a similar graph, one can establish its molecular weight (Fig. 1.13).
Another method that allows you to separate proteins depending on their molecular weight is gel electrophoresis(see above).
Ultracentrifugation. If you shake a vessel filled with sand and water and then place it on a flat surface, the sand will quickly settle to the bottom due to the force of gravity. This will not happen with high-molecular substances in solution, since thermal (Brownian) motion maintains their uniform distribution in the solution. The settling of macromolecules, like grains of sand, will occur only if they are subjected to significant acceleration.
To determine the amino acids that make up proteins, acidic (HC1), alkaline (Ba(OH)2) and enzymatic hydrolysis are used. When pure protein, free of impurities, is hydrolyzed, 20 different amino acids are released.
Amino acids, components of proteins are
a-amino acids. All of them belong to the L-series, and the magnitude and sign of optical rotation depend on the nature of amino acid radicals and the pH value of the solution. D-amino acids are not found in human proteins, but they are found in the cell wall of bacteria, as part of some antibiotics (actinomycins).
Amino acids differ from each other in the chemical nature of the R radical, which does not participate in the formation of a peptide bond.
Modern rational classification of amino acids is based on the polarity of radicals:
Non-polar (hydrophobic)
 |  |
|
 |  |  |
Polar (hydrophilic)
Negatively charged
Found in some proteins amino acid derivatives. The connective tissue protein collagen contains hydroxyproline and oxylysine. Diiodotyrosine is the basis of the structure of thyroid hormones.
Amino acids have a common property - amphoteric(from the Greek amphoteros - two-sided). In the pH range 4.0-9.0, almost all amino acids exist in the form of bipolar ions (zwitterions). Meaning isoelectric point of an amino acid (IEP, pI) calculated by the formula:
.
For monoaminodicarboxylic acids, pI is calculated as half the sum of the pK values (Table 1) of a- and w-carboxyl groups, for diaminomonocarboxylic acids - as half the sum of the pK values of a- and w-amino groups.
There are nonessential amino acids (can be synthesized in the human body), and essential amino acids, which are not formed in the body and must be supplied with food.
Essential amino acids: valine, leucine, isoleucine, lysine, methionine, threonine, tryptophan, phenylalanine.
Essential amino acids: glycine, alanine, asparagine, aspartate, glutamine, glutamate, proline, serine.
Conditionally replaceable(can be synthesized in the body from other amino acids): arginine (from citrulline), tyrosine (from phenylalanine), cysteine (from serine), histidine (with the participation of glutamine).
To discover and quantify amino acids in biological objects, a reaction with ninhydrin is used.
Table 1. Amino acid dissociation constants
| Amino acid | pK 1 | pK 2 | pK 3 |
| Alanya | 2,34 | 9,69 | |
| Arginine | 2,18 | 9,09 | 13,2 |
| Asparagine | 2,02 | 8,80 | |
| Aspartic acid | 1,88 | 3,65 | 9,60 |
| Valii | 2,32 | 9,62 | |
| Histidine | 1,78 | 5,97 | 8,97 |
| Glycine | 2,34 | 9,60 | |
| Glutamine | 2,17 | 9,13 | |
| Glutamic acid | 2,19 | 4,25 | 9,67 |
| Isoleucine | 2,26 | 9,62 | |
| Leucine | 2,36 | 9,60 | |
| Lysine | 2,20 | 8,90 | 10,28 |
| Methionine | 2,28 | 9,21 | |
| Proline | 1,99 | 10,60 | |
| Series | 2,21 | 9,15 | |
| Tyrosine | 2,20 | 9,11 | 10,07 |
| Threonine | 2,15 | 9,12 | |
| Tryptophan | 2,38 | 9,39 | |
| Phenylalanine | 1,83 | 9,13 | |
| Cysteine | 1,71 | 8,33 | 10,78 |
EDUCATIONAL MANUAL
FOR INDEPENDENT PREPARATION
TO CLASSES
IN BIOLOGICAL CHEMISTRY
for students studying in the specialty
Pediatrics
Part I
Central Methodological Council
Smolensk State Medical Academy
Smolensk
UDC: 612.015.
Reviewers: Doctor of Medical Sciences, Professor A.S. Solovyov
Doctor of Medical Sciences, Professor O.V. Molotkov
Educational and methodological manual for self-preparation for classes in biological chemistry for students studying in the specialty of Pediatrics.
Part I / T.G. Makarenko, K.A. Mageenkova
Smolensk SGMA. 2012. - 92 p.
The manual contains a brief summary of the theoretical material of the biochemistry program that is not included in the lecture course, tests to test knowledge, situational problems, and questions for exams. The manual also includes specialized questions on the characteristics of metabolism in children. The manual consists of two parts in accordance with the curriculum for the III and IV semesters. The manual is intended for students studying in the specialty of Pediatrics.
Council of the State Budgetary Educational Institution of Higher Professional Education SGMA Roszdrav of the Russian Federation
Lecture course topics in biochemistry (43 hours)
1. Introduction to biochemistry.
2. Structural organization of proteins.
3. Physico-chemical properties of proteins.
4. Structure, mechanism of action of enzymes.
5. Properties of enzymes.
6. Intramitochondrial oxidation. Energy exchange.
7. Extramitochondrial oxidation.
8. General pathways of catabolism.
9. Anaerobic oxidation of carbohydrates.
10. Aerobic oxidation of carbohydrates. Gluconeogenesis.
11. Pentoso - phosphate pathway.
12. Metabolism of triacylglycerols and glycerophospholipids
13. Metabolism of cholesterol, sphingolipids.
14. Relationship between fat and carbohydrate metabolism. Ketone bodies.
15. General pathways of amino acid metabolism in tissues.
16. Ways to neutralize ammonia in tissues.
17. Exchange of phenylalanine and tyrosine.
18. Exchange of purine and pyrimidine nucleotides.
19. Biochemistry of hormones.
20. Biochemistry of erythrocytes. Exchange of hemoproteins.
21. Physico-chemical properties of blood. Respiratory function of blood.
22. Blood coagulation and anticoagulation systems.
23. Water-salt exchange.
Material for independent work of students
(72 hours of extracurricular work)
The manual is intended for extracurricular independent work on biological chemistry for students of the pediatric faculty.
The manual includes a summary of material from the biological chemistry curriculum for medical students that is not included in the classroom lecture course. For students studying in the specialty of Pediatrics, additional information is provided about the characteristics of metabolism in children. Test assignments for class topics are used for intermediate and final control of knowledge. Discussion of situational problems is expected to be carried out in class with the participation of the teacher. In this regard, comments on situational tasks are not provided in the manual. The manual contains a list of exam questions in biochemistry.
Lesson topic No. 1
AMINO ACID COMPOSITION OF PROTEINS. HYDROLYSIS OF SIMPLE PROTEIN. CHROMATOGRAPHIC SEPARATION OF AMINO ACIDS
2. Goals of independent work: expand ideas about the structural organization of proteins
Understand the biological functions of proteins,
Complete information about the primary, secondary, tertiary, quaternary structure of proteins,
To get acquainted with the peculiarities of the protein composition of tissues in the body of children,
Develop the skill of using acquired knowledge.
4. List of questions and tasks for independent work
Proteins are high-molecular polymeric N-containing organic substances consisting of amino acids connected by peptide bonds and having a complex structural organization.
The term “proteins” is due to the ability of these compounds to produce white precipitates. The name “proteins” comes from protos (Greek) – first, important, and reflects the central role of this class of substances in the body.
Protein content in the human body higher than the content of lipids and carbohydrates. It accounts for 18–20% of the total tissue mass (wet mass). The predominance of proteins in tissues compared to other substances is revealed when calculating the protein content per dry mass of tissues - 40 - 45%. The protein content in different tissues fluctuates within a certain range. The highest protein content is in skeletal muscles (18–23% of wet weight or 80% of dry tissue weight). Adipose tissue has a low protein content (6% wet weight or 4% dry tissue weight).
In childhood the total amount of proteins in the body and their composition are different than in adults. In the fetal body, the total protein content does not exceed 10%. In newborns it makes up 10–12% of body weight. During the neonatal period, there is an increase in the processes of protein breakdown for energy purposes. Because of this, the protein content is temporarily reduced. In early childhood, immature soluble structural proteins predominate. With age, their differentiation into mature functional proteins increases.
Biological functions of proteins varied. They are associated with high protein specificity and the ability to interact with various ligands, receptors, and cell structures.
· Plastic (structural) function - proteins are part of all cellular structures along with nucleic acids, lipids, carbohydrates.
Energy - 1 g of protein provides about 4 kcal
Regulatory functions:
a) enzymatic - more than 2,000 proteins are biological catalysts, regulating the rate of chemical reactions in the body
b) hormonal - some hormones that regulate biochemical and physiological processes in the body are proteins
c) histone proteins in chromatin regulate the activity of DNA genes
d) intracellular protein calmodulin regulates the activity of various enzymes
· Protective (immune) function. Some proteins (immunoglobulins, interferon, lysozyme) have the ability to bind substances foreign to the body.
· Specific functions:
a) contractile (muscle proteins actin and myosin)
b) photoreceptor (retinal protein rhodopsin)
c) blood clotting (blood clotting factor fibrinogen)
d) receptor – proteins are part of cellular receptors
Chemical composition of proteins
Elementary composition of proteins quite varied. They contain many chemicals. However, the obligatory chemical elements are carbon (51 - 55%), oxygen (21 - 23%), nitrogen (16% - the most constant value), hydrogen (6-7%) and sulfur (0.5 - 2%)
Amino acid composition of proteins. Natural proteins contain α amino acids, which differ in the structure of the radical at the α-carbon atom.
Tests
1. The composition of natural proteins includes chemical elements: Calcium. Carbon. Chlorine. Hydrogen. Sodium. Nitrogen. Potassium . Oxygen. Sulfur .
Carbon. Hydrogen. Nitrogen. Oxygen. Sulfur.
3. Substitutions of amino acids lead to significant changes in the biological properties of proteins:
Glutamate to aspartate. Glutamate to valine. Tryptophan to glutamate. Valine to leucine. Glycine to aspartate. Phenylalanine to tryptophan. Serine to threonine. Glycine to alanine.
4. The completion of protein hydrolysis can be judged by:
By dissolving the sediment of denatured protein. By the disappearance of the turbidity of the hydrolyzate. Based on a positive biuret reaction. Based on a positive ninhydrin reaction. Based on a negative ninhydrin reaction. According to Adamkiewicz's positive reaction. Based on a negative biuret reaction. Based on the results of formol titration.
5. The tertiary structure of the protein is stabilized by bonds:
Hydrophobic. Peptide. Disulfide. Ionic .Hydrogen.
6. The secondary structure of proteins is stabilized by bonds:
Disulfide. Peptide. Ionic. Hydrophobic. Hydrogen.
7. Polar functional groups of proteins are:
Carboxyl. Methyl. Phenolic . Amine. Carbonyl. Indolic.
8. Functional groups of amino acids participate in the formation of a peptide bond:
Epsilon-amine. Alpha - amine. Beta - carboxyl. Gamma-carboxyl. Alpha - carboxyl. Thiols.
9. The underlying structure, i.e. determining higher levels of protein structural organization is:
Primary. Secondary. Tertiary. Quaternary.
10. The pronounced species specificity of proteins with the same natural biological properties is due to:
Fundamental differences in amino acid composition. Significant differences in molecular weight. Features of the spatial structure of molecules. When the primary structures are similar, there are individual equivalent amino acid substitutions. When the primary structures are similar, there are individual unequal amino acid substitutions. Differences in the composition of non-protein components.
11. Amino acids are located predominantly on the surface of the protein molecule:
Non-polar amino acids. Polar amino acids. Both groups of amino acids. None of these groups
12. Amino acids are located mainly deep in the protein molecule:
Non-polar amino acids. Polar amino acids. None of these groups. Both groups of amino acids
13. The formation of the 3rd protein structure involves:
Non-polar amino acids. Polar amino acids. Both groups of amino acids . None of these groups
14. The reason for the change in the affinity of hemoglobin for oxygen is:
Changes in the tertiary structure of protomers. Changes in the relative position of protomers. Cooperative changes in protomer conformation
15. Is this statement correct?
Epsilon - the amino group of lysine is involved in the formation of a peptide bond
Yes. No. There is no correct answer
16. Is this statement correct?
Serine and valine radicals have hydrophilic properties
Yes. No. There is no correct answer
17. Chaperones are mainly involved in the formation and maintenance of:
Primary structure of proteins . Tertiary structure of proteins . Secondary structure of nucleic acids
20%. 10-12%. 5%
Situational tasks
1. On a peptide fragment: Tyr - Cis - Leu - Val - Asp - Ala
Name which amino acid radicals can participate in the formation of bonds:
Hydrophobic. Ionic. Disulfide
2. On a peptide fragment: Tyr – Cis – Leu – Val – Asp – Ala
indicate in the formation of which levels of the structural organization of the protein the bonds formed by the radicals of these amino acids participate
3. Red blood cells shaped like a sickle were found in the blood of an African student who was admitted to the clinic with complaints of shortness of breath, dizziness, rapid heartbeat and pain in the limbs.
Explain the reason for the development of this disease.
4. Hemoglobin is a complex oligomeric hemoprotein protein. What post-translational changes lead to the formation of a functionally active protein?
Main
Biochemistry. Ed. E.S. Severina. 2003. pp. 9-28, 31-56.
Biochemistry. A short course with exercises and tasks. 2001. P. 7-25.
AND I. Nikolaev Biological chemistry. 2004. pp. 16-35,38-43.
O.D. Kushmanova. Guide to laboratory exercises in biological chemistry. 1983. pp. 15-19, 19-24.
Lecture material
Additional
T.T. Berezov, B.F. Korovkin. Biological chemistry. 1990. pp. 10-41, 49-59.
R. Murray et al. “Human Biochemistry”. M. "Peace". 1993. p. 21-51(1)
Makarenko T.G., Stunzhas N.M. Educational and methodological manuals “Biochemical characteristics of the child’s body.” Smolensk 2001. 2007.
Makarenko T.G., Stunzhas N.M. A textbook recommended by the educational educational institution “Features of metabolism in newborns and infants.” Smolensk 2012.
A.E. Medvedev “The 22nd genetically encoded amino acid has been discovered” // Vopr. honey. chemistry. 2002. No. 5 -. With. 432
Lesson topic No. 2
SEDIMENTARY REACTIONS TO PROTEINS.
METHODS FOR QUANTITATIVE DETERMINATION OF PROTEINS
2 . Goals of independent work: expand knowledge about the basic physicochemical properties of proteins and their applied medical significance, about methods used in laboratory practice for the quantitative determination of proteins in biological fluids
3. Tasks of independent work:
Be able to evaluate the biomedical significance of the basic physicochemical properties of protein solutions,
Familiarize yourself with the normal protein content in blood serum, with possible deviations and their biochemical interpretation,
To develop the skill of working with new information, its analysis, logical presentation,
In laboratory practice
Optical, colorimetric, and azotometric methods are used to quantify proteins.
Optical methods based on the optical properties of proteins.
These include:
- spectrophotometric methods, estimating the intensity of absorption of UV rays by proteins in the range of about 200 nm and 260 nm. The degree of UVL absorption is proportional to the protein concentration;
- refractometric methods based on the ability of protein solutions to refract light in proportion to their concentration;
- nephelometric methods based on the ability of protein solutions to scatter light in proportion to their concentration;
- polarimetric methods are based on the ability of protein solutions to rotate the plane of polarized light in proportion to their concentration.
Colorimetric methods based on color reactions of proteins - biuret reaction, Lowry method, method of sorption of certain dyes by proteins. The intensity of the color is determined by the concentration of the protein solution.
Nitrometric methods are based on determining the nitrogen content and converting it to protein concentration (proteins contain 16% nitrogen).
Tests
1. Colorimetric methods include:
Nitrometric. Spectrophotometric . Sorption of dyes. Lowry method. Biuret method. Refractometric.
2. The methods of their analysis are based on the ability of proteins to acquire a charge:
X-ray diffraction analysis. Electrophoresis. Ion exchange chromatography. Potentiometric titration. Refractometry. Ultracentrifugation. Column gel filtration.
3. The effect of salting out proteins from solutions is associated with:
With disruption of secondary and tertiary structures. With the breaking of peptide bonds. With loss of charge by proteins. With the dehydration of their molecules. With the formation of a quaternary structure.
4. For the most complete extraction of proteins from tissues of animal origin, you can use the following liquids:
Alcohol-water mixture. Acetone. 10% ammonium sulfate solution. Distilled water. 10% NaCl solution. 10% KCl solution.
5. You can get rid of accompanying low-molecular substances present during protein extraction without losing the proteins’ native properties using the following methods:
Electrophoresis. Dialysis. Column gel - filtration. Precipitation of proteins with trichloroacetic acid.
6. Proteins with different molecular weights can be separated using physical and chemical analysis techniques:
Dialysis. Electrophoresis. Salting out. Potentiometric titration. Column gel filtration.
7. At physiological pH values, an amino acid can gain or lose its charge:
Cysteine. Arginine. Tyrosine. Serin. Histidine. Threonine.
8. The presence of globulins in a solution can be proven:
Electrophoresis. Column gel filtration. Salting out at 50% saturation with ammonium sulfate. Salting out at 100% saturation with ammonium sulfate. Denaturation with urea.
9. The denaturation effect is characterized by the following signs:
Rapid formation of sediment. Loss of biological activity. Preservation of biological properties. Violation of the primary structure of the protein. Slow formation of sediment. Violation of secondary and tertiary structure (conformation). Maintaining conformation.
10. The salting out effect is characterized by the following symptoms:
Reversibility of the effect. Loss of biological properties. Preservation of biological properties. Disturbance of protein conformation. Maintaining protein conformation. Rapid formation of sediment.
11. Protein denaturation is caused by:
Sodium chloride. Sulfuric acid. Lead acetate. Ammonium sulfate. Silver nitrate. Sulfosalicylic acid. Urea. Glucose.
From the potential gradient. From the molecular weight of proteins. From the pH of the environment. From the shape of protein molecules. From the characteristics of the amino acid composition of proteins. From the presence of prosthetic groups in proteins.
13. Using salting out from a mixture of proteins, you can isolate:
Ovaalbumin. Gamma globulin. Serum albumin.
14. The solubility of proteins in water is imparted by functional groups of polypeptide chains:
Carboxyl. Methyl. Phenolic. Amine. Carbonyl. Indolic. Hydroxyl. Thiols. Imminous.
15. The most objective data on the molecular weight of proteins is provided by physicochemical methods:
Cryoscopy. Ebullioscopy. X-ray structural analysis. Ultracentrifugation. Electron microscopy.
16. To accurately determine the protein content in a solution, you can use the optical effect:
Refraction of light rays. Light scattering effect. Optical activity. Absorption of rays in the UV part of the spectrum.
17. When performing gel filtration of proteins, the following are used:
Differences in charge magnitude. Differences in molecular weight . Differences in optical properties
18. In protein electrophoresis, the following are used:
Differences in charge size . Differences in molecular weight . Differences in optical properties
19. A mixture of proteins ceruloplasmin (molecular weight 151,000, isoelectric point 4.4) and γ - globulin (mol. weight 150,000, isoelectric point 6.3) can be separated using the following methods:
Electrophoresis. Gel - filtration. Ion exchange chromatography
20. Refractometric methods for the quantitative determination of proteins are based on the effect of:
Light scattering. Light absorption. Light refraction . Rotations of the plane of polarized light
21. Spectrophotometric methods for the quantitative determination of proteins are based on the effect of:
Light scattering. Light absorption at a certain wavelength. Light refraction. Rotations of the plane of polarized light
22. At the isoelectric point, a protein molecule:
They don't dissociate. E electrically neutral . Moving towards the anode. Break down into polypeptides
23. Proteins are able to form stable aqueous solutions due to the presence of:
Brownian motion Presence of hydrophobic radicals. The presence of charge and hydration shell in protein molecules. All of the above factors
Situational tasks
1. Indicate the direction of movement (to the anode, to the cathode, or remain at the start) of the next peptide
Liz - Gli - Ala - Gli
2. Indicate the direction of movement (to the anode, to the cathode, or remain at the start) of the next peptide
Liz – Glu – Ala – Gli
3. Indicate the direction of movement (to the anode, to the cathode, or remain at the start) of the next peptide
Glu - Gli - Ala - Gli
4. Draw conclusions about the features of the amino acid composition of a protein having an isoelectric point = 4.7
5. What charge in a neutral environment will a protein acquire that has an isoelectric point = 4.7?
Explain your answer.
6. After salting out the protein with ammonium sulfate, a precipitate was obtained containing the protein under study with an admixture of salt. How can you separate protein from salt?
7. Basic and additional literature on the topic
Main
Biochemistry. Ed. E.S. Severina. 2003. pp. 67-74
Biochemistry. A short course with exercises and tasks. 2001. pp. 29-31
AND I. Nikolaev Biological chemistry. 2004. pp. 43-60
O.D. Kushmanova. Guide to laboratory exercises in biological chemistry. 1983. pp. 7-15, 28-29.
Lecture material
Additional
T.T. Berezov, B.F. Korovkin. Biological chemistry. 1990. pp. 37-41.
R. Murray et al. “Human Biochemistry”. M. "Peace". 1993. pp. 43-51 (1)
Yu.E. Veltishchev, M.V. Ermolaev, A.A. Ananenko, Yu.A. Knyazev. "Metabolism in children." M.: Medicine. 1983. 462 p.
R.M. Kohn, K.S. Mouth. Early diagnosis of metabolic diseases. M. "Medicine". - 1986.
Makarenko T.G., Stunzhas N.M. Educational and methodological manuals “Biochemical characteristics of the child’s body.” Smolensk 2001. 2007
Makarenko T.G., Stunzhas N.M. Educational and methodological manual “Features of metabolism in newborns and infants” (Recommended by the UMO). Smolensk 2012.
Titov V.N. Methodological aspects of determining the content of total protein in blood serum // Klin. lab. diagnostics, 1995, - .№ 2.S. 15-18
Lesson topic No. 3
CLASSIFICATION OF PROTEINS.
SIMPLE AND COMPLEX PROTEINS
2. Goals of independent work: consolidate knowledge about the principles of protein classification, properties and compositional features of the main groups of simple and complex proteins
3. Tasks of independent work:
Consider the principles of protein classification,
To study the features of the properties, chemical composition and biological functions of the main groups of simple and complex proteins,
To develop the skill of working with new information, its analysis, logical presentation,
To develop the skill of using acquired knowledge in educational and professional activities.
4. List of questions for independent work
Protein classification
The huge number of proteins in the body, the diversity of their properties and biological functions determine the complexity of their taxonomy.
Classifications of proteins according to structural and functional principles are proposed.
“Today, too much is known about proteins to be satisfied with the old classification, and too little to create a better one” - this definition of the state of the issue of protein classification remains relevant to this day.
In practical terms, the classification of proteins is quite convenient, taking into account the peculiarities of their chemical composition and physicochemical properties.
According to this classification, all proteins are divided into 2 groups: simple (proteins) and complex (proteins.
TO proteins (simple proteins) include proteins consisting only of amino acids.
They, in turn, are divided into groups depending on the physicochemical properties and characteristics of the amino acid composition. The following groups of simple proteins are distinguished:
· albumins,
· globulins,
· protamines,
· histones,
· prolamins,
· glutelins,
· proteinoids.
Albumin – a widespread group of proteins in the tissues of the human body. They have a relatively low molecular weight of 50 – 70 thousand daltons. Albumins in the physiological pH range have a negative charge, since, due to the high content of glutamic acid in their composition, they are in an isoelectric state at pH 4.7. Having a low molecular weight and a pronounced charge, albumins move during electrophoresis at a fairly high speed. The amino acid composition of albumins is diverse; they contain the entire range of essential amino acids. Albumins are highly hydrophilic proteins. They are soluble in distilled water. A powerful hydration shell is formed around the albumin molecule, so a high 100% concentration of ammonium sulfate is required to salt them out of solutions. Albumins perform a structural and transport function in the body and are involved in maintaining the physical and chemical constants of the blood.
Globulins– a widespread group of proteins, usually accompanying albumins. They have a higher molecular weight than albumins - about 200 thousand daltons, therefore they move more slowly during electrophoresis. The isoelectric point of globulins is at pH 6.3 – 7. They are distinguished by a diverse set of amino acids. Globulins are insoluble in distilled water; they are soluble in salt solutions of KCl and NaCl at a concentration of 5–10%. Globulins are less hydrated than albumins, therefore they are salted out of solutions already at 50% saturation with ammonium sulfate. Globulins in the body perform structural, protective, and transport functions.
Histones– have a small molecular weight of 11-24 thousand daltons. They are rich in alkaline amino acids lysine and arginine, therefore they are in an isoelectric state in a sharply alkaline environment at pH 9.5 - 12. Under physiological conditions, histones have a positive charge. In different types of histones, the content of arginine and lysine varies, and therefore they are divided into 5 classes. Histones H1 and H2 are rich in lysine, histones H3 are rich in arginine. Histone molecules are polar, very hydrophilic, and therefore difficult to salt out of solutions. In cells, positively charged histones are typically associated with negatively charged DNA in chromatin. Histones in chromatin form a scaffold onto which the DNA molecule is wound. The main functions of histones are structural and regulatory.
Protamines– low molecular alkaline proteins. Their molecular weight is 4 – 12 thousand daltons. Protamines contain up to 80% arginine and lysine. They are contained in the nucleoproteins of milk fish - klupein (herring), mackerel (mackerel).
Prolamins, glutelins – vegetable proteins rich in glutamic acid (up to 43%) and hydrophobic amino acids, in particular proline (up to 10 - 15%). Due to the peculiarities of their amino acid composition, prolamins and glutelins are insoluble in water and saline solutions, but soluble in 70% ethyl alcohol. Prolamins and glutelins are food proteins of cereals, making up the so-called gluten proteins. Gluten proteins include secalin (rye), gliadin (wheat), hordein (barley), avenin (oats). In childhood, intolerance to gluten proteins may occur, to which antibodies are produced in the intestinal lymphoid cells. Celiac enteropathy develops and the activity of intestinal enzymes decreases. In this regard, it is recommended to administer cereal decoctions to children after 4 months of age. Rice and corn do not contain gluten proteins.
Proteinoids(protein-like) - fibrillar water-insoluble proteins. They are part of supporting tissues (bones, cartilage, tendons, ligaments). They are represented by collagen, elastin, keratin, fibroin.
Collagen ( birth glue ) – A widely distributed protein in the body, it makes up about a third of all proteins in the body. It is part of bones, cartilage, teeth, tendons and other tissues.
The peculiarities of the amino acid composition of collagen include, first of all, a high content of glycine (1/3 of all amino acids), proline (1/4 of all amino acids), and leucine. Collagen contains rare amino acids hydroxyproline and hydroxylysine, but lacks cyclic amino acids.
The polypeptide chains of collagen contain about 1000 amino acids. There are several types of collagen depending on the combination of different types of polypeptide chains in it. The fibril-forming types of collagen include type I collagen (predominant in the skin), type II collagen (predominant in cartilage) and type III collagen (predominant in blood vessels). In newborns, the bulk of collagen is type III, in adults – types II and I.
The secondary structure of collagen is a “broken” alpha helix, the turn of which contains 3.3 amino acids. The helix pitch is 0.29 nm.
Three polypeptide chains of collagen are arranged in the form of a triple twisted rope, fixed by hydrogen bonds, and form the structural unit of collagen fiber - tropocollagen. Tropocollagen structures are arranged in parallel, longitudinally offset rows, fixed by covalent bonds, and form collagen fiber. In the spaces between tropocollagen, calcium is deposited in bone tissue. Collagen fibers contain carbohydrates that stabilize collagen bundles.
Keratins - proteins of hair, nails. They are insoluble in solutions of salts, acids, and alkalis. Keratins contain a fraction that contains a large amount of sulfur-containing amino acids (up to 7–12%), forming disulfide bridges that impart high strength to these proteins. The molecular weight of keratins is very high, reaching 2,000,000 daltons. Keratins can have alpha and beta structures. In alpha keratins, three alpha helices combine into a supercoil to form protofibrils. Protofibrils unite into profibrils, then into macrofibrils. An example of beta keratins is silk fibroin.
Elastin – protein of elastic fibers, ligaments, tendons. Elastin is insoluble in water and cannot swell. Elastin contains a high proportion of glycine, valine, and leucine (up to 25–30%). Elastin is able to stretch under load and restore its size after the load is removed. Elasticity is associated with the presence in elastin of a large number of interchain cross-links with the participation of the amino acid lysine. The two protein chains form a lysyl-norleucine bond. Four protein chains form a bond called desmosine.
TO complex proteins (proteins) include proteins that, in addition to the protein part, contain non-protein substances (prosthetic groups).
Complex proteins are classified according to the chemical composition of their prosthetic group. The following groups of complex proteins are distinguished:
· chromoproteins,
· lipoproteins,
· glycoproteins,
· phosphoproteins,
· metalloproteins.
Chromoproteins contain colored non-protein compounds as a prosthetic group. The group of chromoproteins includes hemoproteins and flavoproteins.
In hemoporotheids The prosthetic group is heme - an organic, iron-containing substance that gives the protein its red color. Heme binds to the protein globin through coordination and hydrophobic bonds. Examples of hemoproteins are erythrocyte protein hemoglobin, muscle protein myoglobin, tissue proteins cytochromes, enzymes catalase, peroxidase. Hemoproteins are involved in oxygen transport and oxidative processes in tissues.
In flavoproteins contains a yellow prosthetic group. The nucleotides FAD and FMN can be represented as a prosthetic group. Flavoproteins include the enzyme succinate dehydrogenase. Some flavoproteins contain metals - metalloflavoproteins. Flavoproteins are involved in oxidative processes in the body.
Nucleoproteins consist of a protein part and nucleic acids: DNA or RNA. Deoxyribonucleoproteins are localized in the nucleus, and ribonucleoproteins are localized in the cytosol. Proteins in the nucleoproteins of the nucleus are represented mainly by histones. The protein and non-protein parts of nucleoproteins are connected by ionic and hydrophobic bonds. With complete hydrolysis of nucleoproteins, amino acids, phosphoric acid, carbohydrates and a purine or pyrimidine nitrogenous base are formed. Nucleoproteins are involved in the storage and reproduction of genetic information.
Lipoproteins They contain various fats as a prosthetic group (triacylglycerols, phospholipids, cholesterol, etc.). Hydrophobic and ionic bonds are formed between the protein and the lipid. Lipoproteins are usually divided into structural, which are part of cell membranes, and transport, which transport fats in the blood. Transport lipoproteins are spherical particles containing hydrophobic fats inside and hydrophilic proteins on the surface. An example of a lipoprotein is the blood clotting factor thromboplastin.
Phosphoproteins contain in their composition residues of phosphoric acid connected to the serine of the protein part by ester bonds. The addition of phosphoric acid to a protein is reversible and is accompanied by the formation or breaking of ionic bonds between phosphoric acid and charged groups of the protein, which changes the biological activity of the phosphoprotein. Phosphoproteins include structural proteins of bone tissue, milk caseinogen, egg white ovotellin, some enzymes (phosphorylase, glycogen synthetase, TAG lipase)
Glycoproteins usually contain , carbohydrate residues (monosaccharides, oligosaccharides) firmly attached by glycosidic bonds. Glycoproteins usually have a mosaic structure in which carbohydrate and protein fragments alternate. The carbohydrate part gives specificity to glycoproteins and determines their resistance to tissue enzymes. Glycoproteins are widely represented in the human body. They are found both in tissues and in biological fluids. Salivary mucin contains up to 15% mannose and galactose. Glycoproteins are some