Protein cu oh 2 equation. Proteins as a form of life. Demonstration of experience from the presentation "Squirrels"

Guidelines for teachers

2. Questions on chemistry to prepare for the seminar must be given to students no later than two weeks before the lesson.

4. The chemistry teacher provides motivation for the lesson, considers the composition and properties of proteins. A biology teacher generalizes and updates knowledge about the structure of protein molecules, their functions and applications.

5. At the end of the lesson, teachers evaluate the students’ work in this lesson. Equipment: code films, overhead projector, screen, overhead projector, slides, chemicals, demonstration table, tables.

Lesson plan (written on the board)

1. Composition and structure of protein.

2. Protein properties (denaturation, renaturation, hydrolysis, color reactions).

3. Functions of protein and its synthesis in the cell.

4. Application of protein, artificial synthesis of peptides.

Chemistry teacher. Today we are conducting an unusual lesson - it covers the problems of chemistry and biology at the same time. The purpose of our lesson is to systematize and deepen knowledge on the topic “Protein”. We pay special attention to the study of proteins, because proteins are the main component of all life on Earth. Remember F. Engels’ statement about what life is: “Wherever we meet life, we find that it is associated with some kind of protein body, and wherever we find any protein body that is not in the process of decomposition , we, without exception, encounter the phenomena of life. Life is a way of existence of protein bodies.” No substance performs such specific and diverse functions in the body as protein.
Let's remember what compounds are called proteins. ( Natural polymers whose monomers are amino acids.)
The study of which process helped to establish the structure of proteins? ( Study of protein hydrolysis.)

What process is called hydrolysis?

What compounds are formed during the hydrolysis of proteins?

What compounds are called amino acids?

How many amino acids are known in nature?

How many amino acids are found in proteins?

A chemistry teacher demonstrates a code film.

Chemistry teacher. Pay attention to the position of the amino group in amino acids. In accordance with the position of the amino group, the amino acids that make up proteins are called a-amino acids. The general formula of any of these amino acids can be written as follows:

On the code film you see two amino acids, one of which contains two carboxyl groups – COOH, the other – two amino groups – NH2. Such acids are called aminodicarboxylic or diaminocarboxylic acids, respectively.
From your chemistry course you know about optical isomers of natural compounds. Almost all proteins contain only L-amino acids.
Amino acids are monomers of proteins. They can connect to each other through an amide (peptide) bond, which is formed with the release of water - this is a condensation reaction.
Let's create an equation for the reaction between the amino acids glycine and alanine.
(Students work independently and then compare their results with the writing on the board or tape.)

The resulting structure is called a dipeptide. A polymer of many amino acids is called a polypeptide.

Biology teacher. Let's continue studying the properties of proteins, but first we'll answer the following questions.

1. How can we explain the diversity of proteins that exists in nature? ( Differences in the composition of amino acids and their different sequence in the polypeptide chain.)

2. What are the levels of organization of a protein molecule? ( Primary – amino acid sequence; secondary – a -spiral or b - folded structure of chain sections; tertiary - the spatial structure of the protein, formed due to the interaction of amino acid residues of remote sections of the chain: a globule for globular proteins, a filamentous structure for fibrillar proteins; quaternary - the union of two or more separate protein molecules.)

3. What type of bond occurs between amino acids in the primary structure? What is another name for this connection? ( Covalent bond. Amide or peptide bond.)

4. What bonds mainly provide the secondary structure of a protein molecule? ( Hydrogen bonds, disulfhydryl bridges.)

5. What connections provide tertiary structure? ( Hydrogen bonds, hydrophobic and ionic interactions.)

6. What bonds provide the quaternary structure of a protein molecule? ( Electrostatic, hydrophobic and ionic interactions.)

7. Give an example of a protein known to you that has a quaternary structure. ( ATPase, hemoglobin.)

Now let's solve the following problem ( the condition of the task is projected through an overhead projector, a slide is shown with blood smears of a healthy person and a patient with sickle cell anemia).
The disease sickle cell anemia is accompanied by the replacement of the amino acid residue glutamic acid in the polypeptide chain of the hemoglobin molecule with a valine residue. Fragment of the chain of normal hemoglobin: – glu–glu–Liz–. Fragment of an abnormal hemoglobin chain: – shaft–glu–Liz– (glu– glutamic acid; Liz– lysine; shaft– valine). Draw these fragments as chemical formulas.

Solution.

Fragment of a chain of normal hemoglobin:

Fragment of an abnormal hemoglobin chain:

From the above example it follows that the primary structure of a protein molecule can determine all its subsequent levels of organization. Changes in the structural organization of a protein can disrupt its functions, which in some cases leads to the development of pathology - disease.
The structure of a protein determines its physicochemical properties, such as solubility.

A chemistry teacher demonstrates a code film.

Classification of proteins according to their solubility

Chemistry teacher. To maintain their functional activity, proteins must have a natural (native) structural organization at all levels.
Disturbances in the primary organization, leading to the rupture of the amide bond with the addition of a water molecule, are called protein hydrolysis. With complete hydrolysis, the protein breaks down into its constituent amino acids.
Violation of the secondary and tertiary structure of the protein, i.e. the loss of its native structure is called protein denaturation.
Protein denaturation is caused by various factors: significant changes in temperature, increasing and decreasing the pH of the environment, exposure to heavy metal ions, and certain chemical compounds, for example, phenols.

A chemistry teacher demonstrates experiments.

Experience 1. Protein + heat -->

Experience 2. Protein + phenol --> denaturation (precipitation).

Experience 3. Protein + Pb or CH 3 COOH --> denaturation (precipitation).

Experience 4. Protein + CuSO4 --> denaturation (precipitation).

Biology teacher. Denaturation occurs as a result of the destruction of hydrogen and disulfide covalent bonds (but not peptide bonds, ionic and hydrophobic interactions), which ensure the formation and maintenance of the secondary and tertiary structures of the protein. In this case, the protein loses its inherent biological properties.
Reactions used to determine the composition of a substance are called qualitative.
What reactions are qualitative to protein?

A chemistry teacher demonstrates the following experiments.

Experience 1. Xanthoprotein reaction (nitration of benzene rings of aromatic amino acids of protein):

protein (cooled) + HNO 3 (conc.) + heat --> yellow color

Experience 2. Biuret reaction (allows you to determine the number of peptide bonds):

protein + CuSO 4 + NaOH --> violet color (urea gives this reaction);
CuSO 4 + NaOH --> Cu(OH) 2 +Na 2 SO 4 ;
protein + Cu(OH) 2 --> violet coloring.

Is it possible to recognize glycerol, protein, and glucose using one reagent? Can! This reagent is copper hydroxide, it gives different colors to solutions of these substances:

a) glycerol + Cu(OH) 2 --> bright blue solution;
b) glucose + Cu(OH) 2 + heating --> red precipitate;
c) protein + Cu(OH) 2 --> violet coloring.

Biology teacher. Name the functions of polypeptides that you know. ( Construction Polypeptides are part of the cell walls of fungi and microorganisms and are involved in the construction of membranes. Hair, nails, and claws are made of keratin protein. Collagen protein is the basis of tendons and ligaments. Another important function of protein is enzymatic, catalytic. Proteins also provide all types of biological mobility. In addition, proteins perform transport, hormonal, or regulatory, receptor, hemostatic, toxigenic, protective and energy functions.)
Define enzymes. ( Enzymes are proteins that have catalytic activity, i.e. accelerating reactions.)
All enzymes are highly specific to their substrate and, as a rule, catalyze only one very specific reaction. Look at the diagrammatic representation of the structure of an enzyme. ( A biology teacher demonstrates a code film with a schematic representation of an enzyme.) Each enzyme has an active site in which the chemical transformation of the reaction substrate occurs. Sometimes there may be several substrate binding sites. The structure of the binding site is complementary to the structure of the substrate, i.e. they fit together “like a key fits a lock.”
The work of enzymes is influenced by numerous factors: pH, temperature, ionic composition of the medium, the presence of small organic molecules that bind to the enzyme or are part of its structure and are otherwise called cofactors (coenzymes). Some vitamins, such as pyridoxine (B 6 ) and cobalamin (B 12 ).

A biology teacher introduces students to the practical use of enzymes.

Clinical significance of enzymes

1. Diseases caused by enzyme deficiency are widely known. Examples: indigestibility of milk (no lactase enzyme); hypovitaminosis (vitamin deficiency) – the lack of coenzymes reduces enzyme activity (hypovitaminosis of vitamin B1 leads to beriberi disease); phenylketonuria (caused by a violation of the enzymatic conversion of the amino acid phenylalanine to tyrosine).

2. Determination of enzyme activity in biological fluids is of great importance for the diagnosis of diseases. For example, viral hepatitis is determined by the activity of enzymes in the blood plasma.

3. Enzymes are used as reagents in the diagnosis of certain diseases.

4. Enzymes are used to treat certain diseases. Examples of some enzyme-based drugs: pancreatin, festal, lidase.

Use of enzymes in industry

1. In the food industry, enzymes are used in the preparation of soft drinks, cheeses, canned food, sausages, and smoked meats.

2. In animal husbandry, enzymes are used in the preparation of feed.

3. Enzymes are used in the production of photographic materials.

4. Enzymes are used in the processing of flax and hemp.

5. Enzymes are used to soften leather in the leather industry.

6. Enzymes are part of washing powders.

Biology teacher. Let's look at other functions of proteins. Motor functions are carried out by special contractile proteins, which include, for example, actin and myosin, which are part of muscle fibers.
Another important function of proteins is transport. Proteins, for example, carry potassium ions, amino acids, sugars and other compounds across the cell membrane into the cell. Proteins are also interstitial carriers.

By regulating the metabolism within cells and between cells and tissues of the whole body, proteins perform a hormonal, or regulatory function. For example, the hormone insulin is involved in the regulation of both protein and fat metabolism.
On the surface of cell membranes there are protein receptors that selectively bind hormones and mediators, thereby performing a receptor function.
The homeostatic function of proteins is to form a clot when stopping bleeding.
Some proteins and peptides released by organisms, such as pathogens or some poisonous animals, are toxic to other living organisms - this is the toxicogenic function of proteins.
The protective function of proteins is very important. Antibodies are proteins that are produced by the body's immune system when it is invaded by a foreign protein, bacteria, or virus. They identify the “stranger” and participate in his destruction.
Proteins that serve as an energy reserve include, for example, casein, the main protein in milk.

Answer the following questions.

2. What causes the rejection of transplanted organs and tissues in patients? ( Antibodies, performing a protective function, recognize the foreign protein of the transplanted organs and cause reactions of its rejection.)

3. Why do boiled eggs never produce a chicken? ( Egg whites have irreversibly lost their native structure due to heat denaturation.)

4. Why does the weight of meat and fish decrease after cooking? ( During heat treatment, denaturation of meat or fish proteins occurs. Proteins become practically insoluble in water and give up a significant part of the water they contain, while the weight of meat decreases by 20–40%.)

5. What does the formation of “flakes” or cloudiness of the broth indicate when cooking meat? ( If meat is immersed in cold water and heated, soluble proteins from the outer layers of the meat are transferred into the water. During cooking, they denature, resulting in the formation of flakes, foam that floats to the surface of the water, or a fine suspension that makes the solution cloudy.)

All protein molecules have a finite lifespan - they break down over time. Therefore, proteins are constantly renewed in the body. In this regard, let us recall the basics of protein biosynthesis. Answer the following questions.

1. Where does protein synthesis occur in the cell? ( On ribosomes.)

2. In which cellular organelle is information about the primary structure of the protein stored? ( In chromosomes, the information carrier is DNA.)

3. What is meant by the term “gene”? ( Nucleotide sequence encoding the synthesis of one protein.)

4. What are the main stages of protein biosynthesis called? ( Transcription, broadcast.)

5. What does transcription consist of? ( This is reading information from DNA by synthesizing messenger RNA that is complementary to the DNA region being read.)

6. In what part of the cell does transcription take place? ( In the core.)

7. What does the broadcast consist of? ( This is the synthesis of protein from amino acids in the sequence recorded in mRNA; it occurs with the participation of transport tRNAs that deliver the corresponding amino acids to the ribosome.)

8. In what part of the cell does translation take place? ( In the cytosol, on ribosomes, in mitochondria.)

Protein biosynthesis occurs in the body throughout life, most intensively in childhood. The intensity of protein synthesis in some cases can be adjusted. The action of many antibiotics is based on the suppression of protein synthesis, including in bacteria that cause the disease. For example, the antibiotic tetracycline prevents tRNA from binding to ribosomes.
Let's listen to brief messages about protein drugs used in modern medicine.

Antihistamines

The modern hectic pace of life is accompanied by an increase in the number of diseases, such as heart attack, hypertension, obesity, and all kinds of allergies. Allergy is the body's excessive sensitivity to specific external irritants. All these diseases are characterized by increased levels of histamine in the blood. Histamines are substances formed by decarboxylation of the amino acid histidine. Antihistamines interfere with this reaction and histamine levels decrease.

Interferon

In the process of evolution, in the fight against viruses, animals have developed a mechanism for the synthesis of the protective protein interferon. The program for the formation of interferon, like any protein, is encoded in DNA in the cell nucleus and is turned on after the cells are infected with a virus. Cooling, nervous shock, and lack of vitamins in food lead to a decrease in the ability to produce interferon. Currently, interferon preparations for medical purposes are made from leukocytes from donor blood or using genetic engineering. Interferon is used to prevent and treat viral infections - influenza, herpes, as well as for malignant neoplasms.

Insulin

Insulin is a protein consisting of 51 amino acids. It is released in response to increased blood glucose levels. Insulin controls carbohydrate metabolism and causes the following effects:

– increasing the rate of conversion of glucose into glycogen;
– acceleration of glucose transfer through cell membranes in muscles and adipose tissue;
– increased protein and lipid synthesis;
– increasing the rate of synthesis of ATP, DNA and RNA.

Insulin is necessary for life, because it is the only hormone that reduces the concentration of glucose in the blood. Insufficient secretion of insulin leads to a metabolic disorder known as diabetes mellitus. Insulin preparations are obtained from the pancreas of cattle or through genetic engineering.

Chemistry teacher. Insulin was the first protein whose primary structure was deciphered. It took almost 10 years to establish the sequence of amino acids in insulin. Currently, the primary structure of a very large number of proteins, including those of a much more complex structure, has been deciphered.
The synthesis of protein substances was first carried out using the example of two pituitary hormones (vasopressin and oxytocin).
Finally, teachers give students grades for their work in chemistry and biology class.

1. In accordance with the substances that need to be identified, known qualitative reactions, reagents and identification features must be indicated.

In our case, we can use the following reactions:

2. Propose in the form of a diagram the most effective sequence for determining these compounds.

3. Indicate the reaction procedure, conditions and write the reaction equation indicating the characteristic identification feature.

As a preliminary test for soluble proteins, you can use reagents that cause denaturation (folding): thermal or chemical.

When solving this problem, analysis options are possible.

Option 1. The sequence for identifying the contents of the bottles can be as follows:

1. We carry out a preliminary test for the presence of proteins. We heat samples of each of the 4 bottles in the flame of an alcohol lamp. In test tubes with protein solutions, denaturation is observed (the protein coagulates and loses solubility). In test tubes with samples of other substances, no changes are observed.

2. We identify proteins using their differences in amino acid composition. We carry out a xanthoprotein reaction with protein samples. In a test tube with an egg white solution, the initially formed yellow precipitate dissolves and an orange color appears, since the egg white contains aromatic acids (tyr, fen, tri). Gelatin does not contain aromatic amino acids; the test for their presence will be negative.

3. We identify the contents of the bottles with glucose and amino acid using the reaction with ninhydrin. A characteristic violet color appears in a test tube containing glycine.

4. Confirm the presence of glucose in the remaining bottle. Glucose is a reducing monosaccharide, so to identify it you can use either the “silver mirror” reaction (when heated in a water bath, a characteristic mirror coating of silver appears on the walls of the test tube) or the “copper mirror” reaction (when heated in the flame of an alcohol lamp, a characteristic oxide precipitate appears copper (I) brick-red color).

Option 2.

1. We determine whether a compound belongs to the group of proteins using the biuret reaction with freshly precipitated copper (II) hydroxide. A characteristic purple ring appears in test tubes containing samples of protein solutions. In a test tube with glucose, the dissolution of a blue precipitate of copper (II) hydroxide and the appearance of a cornflower blue color due to the formation of a complex compound—copper sucrose—are also observed; in a test tube with an amino acid, a dark blue color appears due to the formation of a complex compound—copper glycinate.

2. Confirm the presence of glucose. We heat both test tubes in the flame of an alcohol lamp. In a test tube with glucose, a characteristic brick-red precipitate of copper (II) oxide is formed, since glucose belongs to the group of reducing monosaccharides.

3. We identify proteins using their differences in amino acid composition. We carry out a xantoprotein reaction with new samples of protein solutions (see version 1).

To more accurately identify the amino acid, you can take a new sample and perform a reaction with a solution of ninhydrin.

Other options that differ in the sequence of reactions and reagents cannot be excluded.

1) Biuret reaction(for all proteins)

Protein + CuSO 4 + NaOH bright purple color

СuSO 4 + 2NaOH Cu(OH) 2 + Na 2 SO 4

blue sediment

C = O: Cu: O = C C = O: N

NHOHN:O=C

soluble complex

bright purple

2) Xanthoprotein reaction(for proteins containing AA with an aromatic radical)

protein + HNO 3 (k) yellow precipitate

| || -- H 2 O | ||

N CH C─ + HONO 2 N CH C─

yellow color

If you add a concentrated ammonia solution, an orange color appears because the electron density shifts in nitrobenzene.

3) Cysteine ​​reaction- reaction to an AK residue containing S

Protein + NaOH + Pb(CH 3 COO) 2 PbS + protein

Black color

| Pb + PbS

BIOCATALYSIS

One of the important features of chemical reactions occurring in living organisms is their catalytic nature. A living cell can be thought of as a miniature catalytic reactor. The difference between a cell and a chemist’s flask is that if in a flask all reactions proceed independently (the fundamental principle of independence of reactions is implemented), then in a cell everything happens interconnected.

This does not happen because physical laws are violated or the cell obeys other laws - no, only laws apply in living matter. It’s just that in the process of evolution, nature created an effective apparatus for regulating all cellular reactions, which allows the entire cell to control the ratio of products in such a way that all reactions function optimally.

Thus, all biochemical reactions are reactions catalytic.

Biological catalysts are called enzymes or enzymes.

In principle, the same chemical reactions take place in the cell as in a chemical laboratory, but strict restrictions are imposed on the conditions for the reactions in the cell, namely T = 37 ◦ C and P = 1 atm.

Therefore, often processes that occur in one stage in the laboratory are carried out in several stages in living cells.

The essence of catalytic reactions, despite their diversity, boils down to the fact that the starting materials form with the catalyst intermediate connection, which relatively quickly turns into reaction products, regenerating the catalyst.

Sometimes intermediates can be isolated in pure form, but usually they consist of unstable molecules that can only be detected using very sensitive spectral instruments.

The process involving a catalyst is cyclic or circular.

A measure of enzyme activity - speed(number of moles of substrate undergoing a change in 1 minute per 1 mole of enzyme)

The number of revolutions can reach 10 8.

Quite often, the cycles of several catalysts are combined together, forming a circular process.

Substances S1 and S2 are converted into products P1 and P2. During this transformation, first S1 reacts with a third substance X and catalyst E1, forming intermediate product M1, which in turn is converted by catalyst E2 into intermediate product M2, etc.

The accelerating effect of a catalyst is associated with a decrease in activation energy (this is the additional energy that must be imparted to one mole of a substance in order for the particles of the substance to become reactive and able to overcome the energy barrier of the reaction).

The main properties of enzymes include:

Efficiency, which lies in the degree of acceleration (acceleration by 100 million times).

Increased substrate specificity. Enzymes distinguish the substrate through biological recognition (complementarity).

Increased specificity of the catalyzed reaction. Most enzymes speed up one type of reaction.

Increased specificity for optical isomers (can recognize left-handed and right-handed isomers).

The reason for all the unique properties of enzymes is their spatial structure. Typically these are globular proteins, much larger than the substrate in size. This circumstance leads to the fact that in the process of evolution an active center was formed on the surface of the enzyme, which is complementary to the substrate. This is a lock and key.

Conditionally active centers are divided into: binding and catalytic.

The binding center binds the substrate and optimally orients it in relation to the catalyzed group, while all active groups are concentrated in the catalytic center.

If hydrolysis (of proteins, lipids) is necessary to carry out a reaction, then the catalyzed center is formed by side radicals of AA residues.

In this case, the enzyme consists only of polypeptide chains. However, in addition to hydrolytic reactions, others also occur: redox reactions, transfer reactions of any groups.

In these cases, the enzymes contain a non-protein part. This part is coenzyme(r-factor, prosthetic group). The protein part provides the binding effect, and the coenzyme provides the catalytic effect. Protein part - apoenzyme.

Apoenzyme + coenzyme ↔holoenzyme