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Branched amino acids. Branched chain amino acids. Differences between essential and non-essential amino acids

A fragment of one of the DNA chains has the following structure: GGCTCTAGCTTC. Build mRNA on it and determine the sequence of amino acids in a fragment of molecules

s protein (use the genetic code table for this).

The mRNA fragment has the following structure: GCUAAUGUUCUUUAC. Determine the tRNA anticodons and the amino acid sequence encoded in this fragment. Also write the fragment of the DNA molecule on which this mRNA was synthesized (use the genetic code table for this).

The DNA fragment has the following nucleotide sequence AGCCGACTTGCC.
Determine the nucleotide sequence of the tRNA that is synthesized on this fragment and the amino acid that this tRNA will carry if the third triplet corresponds to the tRNA anticodon. To solve the task, use the genetic code table.

Task No. 1.

A fragment of an mRNA chain has the nucleotide sequence: CCCCCCGCAGUA. Determine the sequence of nucleotides in DNA, anticodons in tRNA, and the sequence of amino acids in a fragment of a protein molecule using the genetic code table.

Task No. 2. A fragment of a DNA chain has the following nucleotide sequence: TACCCTCTCTTG. Determine the nucleotide sequence of the mRNA, the anticodons of the corresponding tRNAs, and the amino acid sequence of the corresponding fragment of the protein molecule using the genetic code table.

Problem No. 3
The nucleotide sequence of the DNA chain fragment is AATGCAGGTCATCA. Determine the sequence of nucleotides in mRNA and amino acids in a polypeptide chain. What will happen in a polypeptide if, as a result of a mutation in a gene fragment, the second triplet of nucleotides is lost? Use the gent.code table
Workshop-solving problems on the topic “Protein biosynthesis” (grade 10)

Problem No. 4
The gene region has the following structure: CGG-AGC-TCA-AAT. Indicate the structure of the corresponding section of the protein, information about which is contained in this gene. How will the removal of the fourth nucleotide from the gene affect the structure of the protein?
Problem No. 5
The protein consists of 158 amino acids. How long is the gene encoding it?
Molecular weight of protein X=50000. Determine the length of the corresponding gene. The molecular weight of one amino acid is on average 100.
Problem No. 6
How many nucleotides does the gene (both strands of DNA) contain in which the 51 amino acid protein insulin is programmed?
Problem No. 7
One of the DNA strands has a molecular weight of 34155. Determine the number of monomers of the protein programmed in this DNA. The average molecular weight of one nucleotide is 345.
Problem No. 8
Under the influence of nitrous acid, cytosine is converted to guanine. How will the structure of the synthesized tobacco mosaic virus protein with the amino acid sequence: serine-glycine-serine-isoleucine-threonine-proline change if all cytosine nucleotides are exposed to acid?
Problem No. 9
What is the molecular weight of a gene (two strands of DNA) if a protein with a molecular weight of 1500 is programmed in one strand? The molecular weight of one amino acid is on average 100.
Problem No. 10
A fragment of a polypeptide chain is given: val-gli-phen-arg. Determine the structure of the corresponding t-RNA, i-RNA, DNA.
Problem No. 11
Given a DNA gene fragment: TCT-TCT-TCA-A... Determine: a) the primary structure of the protein encoded in this region; b) the length of this gene;
c) the primary structure of the protein synthesized after the loss of the 4th nucleotide
in this DNA.
Problem No. 12
How many codons will there be in mRNA, nucleotides and triplets in a DNA gene, and amino acids in a protein if 30 tRNA molecules are given?
Problem No. 13

It is known that all types of RNA are synthesized on a DNA template. The fragment of the DNA molecule on which the region of the central loop of tRNA is synthesized has the following nucleotide sequence: ATAGCTGAACGGACT. Establish the nucleotide sequence of the tRNA region that is synthesized on this fragment and the amino acid that this tRNA will carry during protein biosynthesis if the third triplet corresponds to the tRNA anticodon. Explain your answer. To solve the task, use the genetic code table.

Combining amino acids through peptide bonds creates a linear polypeptide chain called primary protein structure

Considering that 20 amino acids are involved in protein synthesis and the average protein contains 500 amino acid residues, we can talk about an unimaginable number of potential proteins. About 100 thousand different proteins have been found in the human body.

For example, 2 amino acids (alanine and serine) form 2 peptides Ala-Ser and Ser-Ala; 3 amino acids will already give 6 variants of the tripeptide; 20 amino acids – 1018 different peptides in just 20 amino acids long (assuming each amino acid is used only once).

The largest protein currently known is titin- is a component of myocyte sarcomeres, the molecular weight of its various isoforms ranges from 3000 to 3700 kDa. Human soleus titin consists of 38,138 amino acids.

The primary structure of proteins, i.e. the sequence of amino acids in it is programmed by the sequence of nucleotides in DNA. The loss, insertion, or replacement of a nucleotide in DNA leads to a change in the amino acid composition and, consequently, the structure of the synthesized protein.

A section of a protein chain 6 amino acids long (Ser-Cys-Tyr-Lei-Glu-Ala)
(peptide bonds are highlighted with a yellow background, amino acids are highlighted with a frame)

If the change in the amino acid sequence is not lethal, but adaptive or at least neutral, then the new protein can be inherited and remain in the population. As a result, new proteins with similar functions arise. This phenomenon is called polymorphism proteins.

For many proteins, pronounced structural conservatism is detected. For example, the hormone insulin person differs from bullish only three amino acids, from pork– per one amino acid (alanine instead of threonine).

The sequence and ratio of amino acids in the primary structure determines the formation secondary, tertiary And quaternary structures.

Genotypic heterogeneity

As a result of the fact that each gene in humans is present in two copies (alleles) and can be subject to mutations (replacement, deletion, insertion) and recombinations that do not seriously affect the function of the encoded protein, it occurs gene polymorphism and, accordingly, protein polymorphism. Entire families of related proteins emerge that have similar but different properties and functions.

For example, there is about 300 different types of hemoglobin, some of them are necessary at different stages of ontogenesis: for example, HbP is embryonic, formed in the first month of development, HbF is fetal, necessary for more later fetal development, HbA and HbA2 – adult hemoglobin. Diversity is ensured by the polymorphism of globin chains: hemoglobin P contains 2ξ and 2ε chains, HbF contains 2α and 2γ chains, HbA contains 2α and 2β chains, and HbA2 contains 2α and 2δ chains.

At sickle cell anemia in the sixth position of the hemoglobin β-chain, glutamic acid is replaced by valine. This leads to synthesis hemoglobin S (HbS)- a hemoglobin that polymerizes in deoxy form and forms strands. As a result, red blood cells become deformed, take on the shape of a sickle (banana), lose elasticity and are destroyed when passing through capillaries. This ultimately leads to decreased tissue oxygenation and necrosis.

AB0 blood groups depend on the structure of a special carbohydrate on the red blood cell membrane. Differences in carbohydrate structure are due to different specificity and activity glycosyl transferase enzyme, capable of modifying the original oligosaccharide. The enzyme has three variants and attaches either N-acetylgalactose or galactose to the oligosaccharide of erythrocyte membranes, or the enzyme does not attach additional saccharide groups (group 0).
As a result, persons with blood group A0 have an oligosaccharide with N-acetylgalactosamine attached to it on their red blood cells, those with blood group B0 have an oligosaccharide with galactose, 00 have only “pure” oligosaccharide, those with blood group AB have an oligosaccharide and N-acetylgalactosamine, and with galactose.

Sali believes there is a growing problem among strength athletes and bodybuilders with excessive intake of branched chain amino acids. Branched chain amino acids, to refresh your memory, are el-leucine, el-isoleucine, el-valine. These are the amino acids that your muscles especially crave. They make up up to 35% of your muscle composition.
"This unbalanced intake interferes with the levels of other key amino acids, causing relative deficiency," says Sali. "At the same time, some individuals often neglect adequate amounts of important vitamins and minerals. Many people do not take enough vitamin A, E and B-complex, or calcium and magnesium.
Quite a few athletes have told me that as soon as they take branched chain amino acids, they feel like they're fine. But they may not be okay. They may cause muscle fatigue, tremors, spasms, injuries, depression or irritability. The trick is to ensure that there is a balance between all your nutrients."
Constant tension as a result intensive training can have a negative impact on you if you don't prepare yourself correctly. The body may find itself "unable to rid itself of the excess lactic acid that accumulates. You begin to feel agitated, restless, nervous. Or perhaps depressed. You will wonder what you did wrong. You think you will overcome it, by exercising more.
"But by doing so, you are plunging yourself into even deeper biochemical imbalances and deficiencies. You have not realized that stress, physical or emotional, depletes your amino acids and other key nutrients."
There is no easy solution to this situation, Sali says. Each case is individual and requires detailed knowledge of lifestyle, diet, stress levels, training intensity and other factors in order to adjust them.

Don't take too much!

Another word of caution against branched-chain amino acids: Many strength athletes and bodybuilders ruin their training benefits by taking too much of them.
Excessive intake may contribute to the accumulation of toxic ammonia, a byproduct of protein turnover in muscle tissue. This can lead to fatigue. For best results Follow the dosage recommendations on the amino acid label.
If you are taking branched chain amino acids, do not take them at the same time as el-tyrosine. Branched chain amino acids can block the absorption of this very amino acid.
Let's take a closer look at some other amino acids and their benefits:

· El Alanin. Included in energy metabolism and helps regulate blood sugar. It is said to raise energy levels. If you are under stress or suffering from hypoglycemia, your body will break down muscle tissue to obtain amino acids such as El-Alanine to raise blood sugar levels.

· El-Asparagine. Important factor in metabolic activity nervous system. El-Aspartic acid. Included in the conversion of carbohydrates into muscle energy. The building block of immunoglobulins and antibodies of the immune system. Combines with other amino acids to form toxin eaters in the circulatory system.

· El Citrulline. Helps detoxify ammonia, a byproduct of protein metabolism.

· El Cysteine. Performs detoxification tasks in combination with el-aspartic acid and el-citrulline. Helps produce protection against the harmful effects of alcohol and tobacco. There are reports of stimulation of hair growth.

· El Cistine. A major partner in tissue antioxidant mechanisms that help prevent the formation of potentially dangerous toxic factors that constantly develop within the body as a result of a wide variety of causes. Promotes acceleration of healing, reduces pain from inflammation, strengthens connective tissue.

· El Glutamia. Lymphocytes and other white blood cells, the first line attackers of the immune system, are highly dependent on glutamine; British researchers have found that extreme endurance activity, say a marathon, can reduce the flow of glutamine to lymphocytes. Glutamine, along with other certain amino acids, is used as fuel in long-distance racing. Until glutamine deficiency is corrected through proper nutritional supplementation, the body remains susceptible to infections.
Glutamine promotes memory and stimulates intelligence and concentration. It has also been shown to be effective in reducing cravings for alcohol and sweets.

· Glycine. It is the smallest of all amino acids, but it is also one of the most important. Its basic function is related to the production of non-essential amino acids and the structure of red blood cells. Glucose and creatine, two substances important for energy production, require glycine for their synthesis. Its deficiency results in a loss of energy.
Glycine has a calming effect and is effectively used for manic depression and aggressive conditions.
People with a sweet tooth can also reduce their sugar cravings. They can break the glycine capsule and sprinkle the sweet-tasting powder onto their food.

· El-Histidine. Together with growth hormone and other certain amino acids, El-histidine is important for tissue growth. It plays a role in the production of red and white blood cells. Used in the treatment of anemia.

· El Lisin. Low levels can slow down protein synthesis and damage muscles and connective tissue. It has an inhibitory effect on viruses and can be used in the treatment of lichen. Lysine and vitamin C together form El-Carnitine, a biochemical that allows muscle cells to use oxygen more efficiently, thereby promoting aerobic performance.

· El Metnonan. Helps remove toxic waste from your liver and aids liver and kidney tissue regeneration.

· El Prolin. The main factor in the formation of connective tissues. It is also mobilized for muscle energy.

· El-phenylalanine. It facilitates absorption, memory, mental acuity and is a major element in the production of collagen, the main fibrous protein tissue in the body.

· El Serin. Important for cellular energy production and the formation of acetylcholine, an essential brain chemical that promotes memory and nervous system function.

· El Treonin. One of the detoxifying amino acids. Prevents the accumulation of fat in the liver. An important component of collagen.

L-carnitine

L-carnitine (l-carnitine, L-carnitine) is a so-called amino acid and vitamin Bt. L-carnitine (L-carnitine) acts as a receptor and storage substance for activated fatty acids in cellular metabolism and, as a result, L-carnitine (L-carnitine) plays a decisive role in the breakdown of fats and energy production. In clinical studies, l-carnitine (L-carnitine) was effective in significant weight loss, significant reduction in body mass index (indicating a significant approach to ideal weight) and a significant reduction in body fat content when used as a component in general program weight loss. L-carnitine (L-carnitine) is also effective for weight management when used in conjunction with other dietary treatments such as chromium picolinate (chromium), and dietary fiber. L-carnitine (L-carnitine) helps with weight management by increasing the rate at which fatty acids are broken down, increasing the residual metabolic rate (the rate at which the body burns calories to maintain body functions), promoting protein (muscle) synthesis. and, if possible, causing appetite suppression. In addition, l-carnitine (L-carnitine) may protect the heart from cardiac ischemia (reduced blood flow during angina, which can significantly weaken the mechanical functioning of the heart and lead to a heart attack) and reduce the duration or severity of a heart attack. L-carnitine (L-carnitine) is also useful for people who suffer from chest sore throat (pain chest similar to cardiac ischemia pain) and may improve exercise capacity in these cases. During prolonged exercise, the use of l-carnitine (L-carnitine) can increase VO2max (maximum aerobic energy that can be achieved), which translates into an increase during prolonged exercise. L-carnitine (l-carnitine, L-carnitine) also reduces the respiration rate (RQ is a conductor to the nutrient mixture that is used for energy). The significance of the decrease in blood pressure, which is caused by the action of L-carnitine (l-carnitine, L-carnitine), is an increase in the use of fat during muscle work with a possible carbon (glycogen) saving effect. Carbon savings will delay the onset of depletion, and thus extend runtime physical activity. The use of L-carnitine (L-carnitine) before physical activity reduces the accumulation of lactic acid, thereby lowering the threshold for the onset of fatigue. In addition, taking L-carnitine (L-carnitine) is useful for relieving muscle pain after exercise.

The main use of L-carnitine is to combat obesity. The easiest way to get rid of excess weight is to eat low-calorie foods and exercise vigorously. However, when stopping the diet, the hated kilograms inexorably return to the most undesirable places: thighs, stomach, buttocks. It is in order to fully burn fat that L-carnitine is needed. It transports fatty acids into the mitochondria of cells, where it occurs<сжигание>fats are fuel for energy production. When fats, rather than carbohydrates and proteins, are oxidized, more energy is released and the functional activity of the cell increases, which preserves glycogen and its building material - protein.

With L-carnitine you gain elastic muscles instead of fat folds!!!

L-carnitine has a significant effect on metabolism. It improves energy metabolism, thereby strengthening the vitality of the body, and prevents cardiovascular diseases. Slows down, to a certain extent, the aging process, strengthens the immune system, stimulates the process of hematopoiesis and the release of oxygen by red blood cells, removes poisons from cells and protects them from many harmful substances, and even counteracts the formation of tumors.

Amino acid structure

Amino acids- heterofunctional compounds that necessarily contain two functional groups: amino group -NH 2 and carboxyl group -COOH, associated with a hydrocarbon radical.

The general formula of the simplest amino acids can be written as follows:

Because amino acids contain two different functional groups that influence each other, the characteristic reactions differ from those of carboxylic acids and amines.

Properties of amino acids

The amino group -NH 2 determines basic properties of amino acids, because it is capable of attaching a hydrogen cation to itself via a donor-acceptor mechanism due to the presence of a free electron pair at the nitrogen atom.

-COOH group (carboxyl group) determines the acidic properties of these compounds. Therefore, amino acids are amphoteric organic compounds.

They react with alkalis as acids:

With strong acids such as amine bases:

In addition, the amino group in an amino acid interacts with its carboxyl group, forming an internal salt:

The ionization of amino acid molecules depends on the acidic or alkaline nature of the environment:

Since amino acids in aqueous solutions behave like typical amphoteric compounds, in living organisms they play the role of buffer substances that maintain a certain concentration of hydrogen ions.

Amino acids are colorless crystalline substances that melt and decompose at temperatures above 200 °C. They are soluble in water and insoluble in ether. Depending on the R- radical, they can be sweet, bitter or tasteless.

Amino acids are divided into natural(found in living organisms) and synthetic. Among natural amino acids (about 150), proteinogenic amino acids (about 20) are distinguished, which are part of proteins. They are L-shapes. About half of these amino acids are irreplaceable, because they are not synthesized in the human body. Essential acids are valine, leucine, isoleucine, phenylalanine, lysine, threonine, cysteine, methionine, histidine, tryptophan. These substances enter the human body with food. If their quantity in food is insufficient, the normal development and functioning of the human body is disrupted. In certain diseases, the body is unable to synthesize some other amino acids. Thus, in phenylketonuria, tyrosine is not synthesized.

The most important property of amino acids is the ability enter into molecular condensation releasing water And formation of amide group -NH-CO-, For example:

The high-molecular compounds obtained as a result of this reaction contain a large number of amide fragments and are therefore called polyamides.

These, in addition to the synthetic nylon fiber mentioned above, include, for example, enant, formed during the polycondensation of aminoenanthic acid. Amino acids with amino and carboxyl groups at the ends of the molecules are suitable for producing synthetic fibers.

Polyamides of α-amino acids are called peptides. Depending on the number of amino acid residues, dipeptides, tripeptides, and polypeptides are distinguished. In such compounds the -NH-CO- groups are called peptide.

Isomerism and nomenclature of amino acids

Amino acid isomerism determined by the different structure of the carbon chain and the position of the amino group, for example:

Amino acid names in which the position of the amino group is designated are also widespread. letters of the Greek alphabet: α, β, γ, etc. Thus, 2-aminobutanoic acid can also be called an α-amino acid:

20 amino acids are involved in protein biosynthesis in living organisms.

Squirrels

Squirrels- these are high-molecular (molecular weight varies from 5-10 thousand to 1 million or more) natural polymers, the molecules of which are built from amino acid residues connected by an amide (peptide) bond.

Proteins are also called proteins(Greek “protos” - first, important). The number of amino acid residues in a protein molecule varies greatly and sometimes reaches several thousand. Each protein has its own inherent sequence of amino acid residues.

Proteins perform diverse biological functions: catalytic (enzymes), regulatory (hormones), structural (collagen, fibroin), motor (myosin), transport (hemoglobin, myoglobin), protective (immunoglobulins, interferon), storage (casein, albumin, gliadin) and others.

The performance of certain specific functions by proteins depends on the spatial configuration of their molecules; in addition, it is energetically unfavorable for the cell to keep proteins in an unfolded form, in the form of a chain, therefore polypeptide chains undergo folding, acquiring a certain three-dimensional structure, or conformation. There are 4 levels of spatial organization of proteins.

Proteins are the basis of biomembranes, the most important component of the cell and cellular components. They play a key role in the life of the cell, constituting, as it were, the material basis of its chemical activity.

The exceptional property of protein is self-organization of structure, i.e. its ability to spontaneously create a certain spatial structure characteristic only of a given protein. Essentially, all the activities of the body (development, movement, performance of various functions, and much more) are associated with protein substances. It is impossible to imagine life without proteins.

Proteins are the most important component of food for humans and animals. supplier of essential amino acids.

Protein structure

In the spatial structure of proteins great importance has character radicals(residues) R- in amino acid molecules. Non-polar radicals amino acids are usually located inside the protein macromolecule and determine hydrophobic interactions; polar radicals, containing ionic (ion-forming) groups, are usually found on the surface of a protein macromolecule and characterize electrostatic (ionic) interactions. Polar nonionic radicals(for example, containing alcohol OH groups, amide groups) can be located both on the surface and inside the protein molecule. They participate in education hydrogen bonds.

In protein molecules, a-amino acids are linked to each other by peptide (-CO-NH-) bonds:

Polypeptide chains constructed in this way or separate areas inside the polypeptide chain can, in some cases, be additionally linked to each other by disulfide (-S-S-) bonds or, as they are often called, disulfide bridges.

Play a major role in creating the structure of proteins ionic(salt) and hydrogen bonds, and hydrophobic interaction- a special type of contact between the hydrophobic components of protein molecules in an aqueous environment. All these bonds have varying strengths and ensure the formation of a complex, large protein molecule.

Despite the difference in the structure and functions of protein substances, their elemental composition varies slightly (in% by dry weight): carbon - 51-53; oxygen - 21.5-23.5; nitrogen - 16.8-18.4; hydrogen - 6.5-7.3; sulfur - 0.3-2.5.

Some proteins contain small amounts of phosphorus, selenium and other elements. The sequence of amino acid residues in a polypeptide chain is called the primary structure of the protein. A protein molecule can consist of one or more polypeptide chains, each of which contains a different number of amino acid residues. Given the number of possible combinations, the variety of proteins is almost limitless, but not all of them exist in nature. The total number of different types of proteins in all types of living organisms is 10 11 -10 12. For proteins whose structure is characterized by exceptional complexity, in addition to the primary one, more high levels structural organization: secondary, tertiary, and sometimes quaternary structures.

Secondary structure most proteins possess, although not always along the entire length of the polypeptide chain. Polypeptide chains with a certain secondary structure can be differently located in space.

In formation tertiary structure In addition to hydrogen bonds, ionic and hydrophobic interactions play an important role. Based on the nature of the “packaging” of the protein molecule, a distinction is made between globular, or spherical, and fibrillar, or filamentous, proteins.

For globular proteins, an α-helical structure is more typical; the helices are curved, “folded.” The macromolecule has a spherical shape. They dissolve in water and saline solutions to form colloidal systems. Most proteins in animals, plants and microorganisms are globular proteins.

- the sequence of arrangement of amino acid residues in the polypeptide chain that makes up the protein molecule. The bond between amino acids is a peptide bond.

If a protein molecule consists of only 10 amino acid residues, then the number of theoretically possible variants of protein molecules, differing in the order of alternation of amino acids, is 1020. Having 20 amino acids, you can make up an even larger number of different combinations from them. About ten thousand different proteins have been found in the human body, which differ both from each other and from the proteins of other organisms.

Exactly primary structure of a protein molecule determines the properties of protein molecules and its spatial configuration. Replacing just one amino acid with another in a polypeptide chain leads to a change in the properties and functions of the protein. For example, replacing the sixth glutamine amino acid in the β-subunit of hemoglobin with valine leads to the fact that the hemoglobin molecule as a whole cannot perform its main function - oxygen transport; In such cases, a person develops a disease - sickle cell anemia.

Secondary structure- ordered folding of the polypeptide chain into a spiral (looks like an extended spring). The turns of the helix are strengthened by hydrogen bonds that arise between carboxyl groups and amino groups. Almost all CO and NH groups take part in the formation of hydrogen bonds. They are weaker than peptide ones, but, repeated many times, impart stability and rigidity to this configuration. At the level of secondary structure, there are proteins: fibroin (silk, spider web), keratin (hair, nails), collagen (tendons).

Tertiary structure- packing of polypeptide chains into globules, resulting from the formation of chemical bonds (hydrogen, ionic, disulfide) and the establishment of hydrophobic interactions between radicals of amino acid residues. The main role in the formation of the tertiary structure is played by hydrophilic-hydrophobic interactions.

In aqueous solutions, hydrophobic radicals tend to hide from water, grouping inside the globule, while hydrophilic radicals, as a result of hydration (interaction with water dipoles), tend to appear on the surface of the molecule. In some proteins, the tertiary structure is stabilized by disulfide covalent bonds formed between the sulfur atoms of two cysteine residues. At the tertiary structure level there are enzymes, antibodies, and some hormones.

Quaternary structure characteristic of complex proteins whose molecules are formed by two or more globules. The subunits are held in the molecule by ionic, hydrophobic, and electrostatic interactions. Sometimes, during the formation of a quaternary structure, disulfide bonds occur between subunits. The most studied protein with a quaternary structure is hemoglobin. It is formed by two α-subunits (141 amino acid residues) and two β-subunits (146 amino acid residues). Associated with each subunit is a heme molecule containing iron.

If for some reason the spatial conformation of proteins deviates from normal, the protein cannot perform its functions. For example, the cause of “mad cow disease” (spongiform encephalopathy) is the abnormal conformation of prions, the surface proteins of nerve cells.

For fibrillar proteins, a filamentous structure is more typical. They are generally insoluble in water. Fibrillar proteins usually perform structure-forming functions. Their properties (strength, stretchability) depend on the method of packing the polypeptide chains. Examples of fibrillar proteins are myosin and keratin. In some cases, individual protein subunits form complex ensembles with the help of hydrogen bonds, electrostatic and other interactions. In this case, it is formed quaternary structure of proteins.

An example of a protein with a quaternary structure is blood hemoglobin. Only with such a structure does it perform its functions - binding oxygen and transporting it to tissues and organs. However, it should be noted that in the organization of higher protein structures, an exclusive role belongs to the primary structure.

Protein classification

There are several classifications of proteins:

By degree of difficulty (simple and complex).

According to the shape of the molecules (globular and fibrillar proteins).

According to solubility in individual solvents (water-soluble, soluble in dilute saline solutions - albumins, alcohol-soluble - prolamins, soluble in dilute alkalis and acids - glutelins).

According to the functions performed (for example, storage proteins, skeletal proteins, etc.).

Properties of proteins

Proteins - amphoteric electrolytes. At a certain pH value (called the isoelectric point), the number of positive and negative charges in the protein molecule is equal. This is one of the main properties of protein. Proteins at this point are electrically neutral, and their solubility in water is the lowest. The ability of proteins to reduce solubility when their molecules reach electrical neutrality is used for isolation from solutions, for example, in the technology for obtaining protein products.

Hydration. The process of hydration means the binding of water by proteins, and they exhibit hydrophilic properties: they swell, their mass and volume increase. The swelling of individual proteins depends solely on their structure. The hydrophilic amide (-CO-NH-, peptide bond), amine (-NH 2) and carboxyl (-COOH) groups present in the composition and located on the surface of the protein macromolecule attract water molecules, strictly orienting them on the surface of the molecule. The hydration (aqueous) shell surrounding protein globules prevents aggregation and sedimentation, and therefore contributes to the stability of protein solutions. At the isoelectric point, proteins have the least ability to bind water; the hydration shell around protein molecules is destroyed, so they combine to form large aggregates. Aggregation of protein molecules also occurs when they are dehydrated with the help of certain organic solvents, for example, ethyl alcohol. This leads to the precipitation of proteins. When the pH of the environment changes, the protein macromolecule becomes charged and its hydration capacity changes.

With limited swelling, concentrated protein solutions form complex systems called jellies. Jellies are not fluid, elastic, have plasticity, a certain mechanical strength, and are able to retain their shape. Globular proteins can be completely hydrated and dissolved in water (for example, milk proteins), forming solutions with low concentrations. The hydrophilic properties of proteins, i.e. their ability to swell, form jellies, stabilize suspensions, emulsions and foams, are of great importance in biology and the food industry. A very mobile jelly, built mainly from protein molecules, is cytoplasm - raw gluten isolated from wheat dough; it contains up to 65% water.

Various hydrophilicity Gluten proteins are one of the signs characterizing the quality of wheat grain and flour obtained from it (the so-called strong and weak wheat). The hydrophilicity of grain and flour proteins plays an important role in the storage and processing of grain and in baking. The dough, which is obtained in bakery production, is a protein swollen in water, a concentrated jelly containing starch grains.

Denaturation of proteins. During denaturation under the influence of external factors (temperature, mechanical stress, the action of chemical agents and a number of other factors), a change occurs in the secondary, tertiary and quaternary structures of the protein macromolecule, i.e. its native spatial structure. The primary structure, and therefore the chemical composition of the protein, does not change. Physical properties change: solubility and hydration ability decrease, biological activity is lost. The shape of the protein macromolecule changes and aggregation occurs. At the same time, the activity of certain chemical groups increases, the effect of proteolytic enzymes on proteins is facilitated, and therefore it is more easily hydrolyzed.

In food technology, it is of particular practical importance thermal denaturation of proteins, the degree of which depends on temperature, duration of heating and humidity. This must be remembered when developing heat treatment regimes for food raw materials, semi-finished products, and sometimes finished products. Thermal denaturation processes play a special role in blanching plant materials, drying grain, baking bread, and producing pasta. Protein denaturation can also be caused by mechanical action (pressure, rubbing, shaking, ultrasound). Finally, the denaturation of proteins is caused by the action of chemical reagents (acids, alkalis, alcohol, acetone). All these techniques are widely used in food and biotechnology.

Foaming. The foaming process refers to the ability of proteins to form highly concentrated liquid-gas systems called foams. The stability of foam, in which protein is a foaming agent, depends not only on its nature and concentration, but also on temperature. Proteins are widely used as foaming agents in the confectionery industry (marshmallows, marshmallows, soufflés). Bread has a foam structure, and this affects its taste.

Protein molecules, under the influence of a number of factors, can collapse or interact with other substances with the formation of new products. For the food industry, two important processes can be distinguished:

1) hydrolysis of proteins under the action of enzymes;

2) interaction of amino groups of proteins or amino acids with carbonyl groups of reducing sugars.

Under the influence of protease enzymes that catalyze the hydrolytic breakdown of proteins, the latter break down into simpler products (poly- and dipeptides) and ultimately into amino acids. The rate of protein hydrolysis depends on its composition, molecular structure, enzyme activity and conditions.

Protein hydrolysis. The hydrolysis reaction with the formation of amino acids in general can be written as follows:

Combustion. Proteins burn to produce nitrogen, carbon dioxide and water, as well as some other substances. Combustion is accompanied by the characteristic smell of burnt feathers.

Color reactions. For the qualitative determination of protein, the following reactions are used:

1. Denaturation– the process of disrupting the natural structure of a protein (destruction of the secondary, tertiary, quaternary structure).

2. Hydrolysis- destruction of the primary structure in an acidic or alkaline solution with the formation of amino acids.

3.Qualitative reactions of proteins:

· biuret;

Biuret reaction– violet coloration when exposed to copper (II) salts in an alkaline solution. This reaction is given by all compounds containing a peptide bond, in which weakly alkaline solutions of proteins interact with a solution of copper (II) sulfate to form complex compounds between Cu 2+ ions and polypeptides. The reaction is accompanied by the appearance of a violet-blue color.

· xanthoprotein;

Xanthoprotein reaction– the appearance of a yellow color under the action of concentrated nitric acid on proteins containing aromatic amino acid residues (phenylalanine, tyrosine), during which the interaction of aromatic and heteroatomic cycles in the protein molecule with concentrated nitric acid occurs, accompanied by the appearance of a yellow color.

· reaction for determining sulfur in proteins.

Cysteine reaction(for proteins containing sulfur) - boiling a solution of protein with lead(II) acetate, causing a black color to appear.

Reference material for taking the test:

Mendeleev table

Solubility table

Having worked through these topics, you should be able to:

Describe the concepts below and explain the relationships between them:
- polymer, monomer;
- carbohydrate, monosaccharide, disaccharide, polysaccharide;
- lipid, fatty acid, glycerol;
- amino acid, peptide bond, protein;
- catalyst, enzyme, active site;
- nucleic acid, nucleotide.
List 5-6 reasons that make water such an important component of living systems.
Name the four main classes of organic compounds found in living organisms; describe the role of each of them.
Explain why enzyme-controlled reactions depend on temperature, pH, and the presence of coenzymes.
Explain the role of ATP in the energy economy of the cell.
Name the starting materials, main steps and end products of light-induced reactions and carbon fixation reactions.
Give a brief description of the general scheme of cellular respiration, from which it would be clear what place the reactions of glycolysis, the H. Krebs cycle (citric acid cycle) and the electron transport chain occupy.
Compare respiration and fermentation.
Describe the structure of the DNA molecule and explain why the number of adenine residues is equal to the number of thymine residues, and the number of guanine residues is equal to the number of cytosine residues.
Make a brief diagram of RNA synthesis from DNA (transcription) in prokaryotes.
Describe the properties of the genetic code and explain why it should be a triplet code.
Based on the given DNA chain and codon table, determine the complementary sequence of the messenger RNA, indicate the codons of the transfer RNA and the amino acid sequence that is formed as a result of translation.
List the stages of protein synthesis at the ribosome level.

Algorithm for solving problems.

Type 1. Self-copying of DNA.

One of the DNA chains has the following nucleotide sequence:
AGTACCGATACCGATTTACCG...
What nucleotide sequence does the second chain of the same molecule have?

To write the nucleotide sequence of the second strand of a DNA molecule, when the sequence of the first strand is known, it is enough to replace thymine with adenine, adenine with thymine, guanine with cytosine, and cytosine with guanine. Having made this replacement, we get the sequence:
TATTGGGCTATGAGCTAAAATG...

Type 2. Protein coding.

The chain of amino acids of the ribonuclease protein has the following beginning: lysine-glutamine-threonine-alanine-alanine-alanine-lysine...
What nucleotide sequence does the gene corresponding to this protein begin with?

To do this, use the genetic code table. For each amino acid, we find its code designation in the form of the corresponding triple of nucleotides and write it down. By arranging these triplets one after another in the same order as the corresponding amino acids, we obtain the formula for the structure of a section of messenger RNA. As a rule, there are several such triplets, the choice is made according to your decision (but only one of the triplets is taken). Accordingly, there may be several solutions.
ААААААААЦУГЦГГЦУГЦГАAG

What sequence of amino acids does a protein begin with if it is encoded by the following sequence of nucleotides:
ACCTTCCATGGCCGGT...

Using the principle of complementarity, we find the structure of a section of messenger RNA formed on a given segment of a DNA molecule:
UGGGGGUACGGGGCA...

Then we turn to the table of the genetic code and for each triple of nucleotides, starting from the first, we find and write out the corresponding amino acid:
Cysteine-glycine-tyrosine-arginine-proline-...

Ivanova T.V., Kalinova G.S., Myagkova A.N. "General Biology". Moscow, "Enlightenment", 2000