Many of us know that proteins are necessary for the body, as they contain amino acids. But not everyone understands what these elements are and why their presence in the diet is so important. Today we will find out how many amino acids are included in how they are classified and what function they perform.

What are amino acids?

So, amino acids (aminocarboxylic to-you) are organic compounds that are the main element that forms the structure of the protein. Proteins, in turn, take part in all physiological processes of the human body. They form bones, tendons, ligaments, internal organs, muscles, nails and hair. Proteins become part of the body in the process of synthesis of amino acids that come with food. Therefore, it is not protein that is an important nutrient, but amino acids. And not all proteins are equally useful, because each of them has its own unique composition of these same acids.

Quite complicated, let's consider it at a basic level. We know that aminocarboxylic acids are the building blocks of the building called protein and the metropolis called man. However, not all proteins have exactly the elements that we need. If you look at a protein under a microscope, you can see a chain of amino acids connected by peptide bonds. Roughly speaking, the links of this chain serve as a repair and building material in our body.

Surprisingly, there was a time when scientists didn't know how many different amino acids are in proteins. Most of them were opened in the 19th and the rest in the 20th century. It took scientists 119 years to finally answer the question: "How many amino acids are in a protein?" The structure of each of them was studied even longer.

To date, it is known that 20 proteinogenic aminocarboxylic acids are necessary for the normal functioning of the human body. These twenty are often called major acids. From the point of view of chemistry, they are classified according to many criteria. But ordinary people are closest to the classification according to the ability of acids to be synthesized in our body. On this basis, amino acids are interchangeable and irreplaceable.

This classification has some drawbacks. For example, arginine is considered essential in some physiological states, but it can be synthesized by the body. And histidine is replenished in such small quantities that it still needs to be taken with food.

Now that we know how many types of amino acids are included in proteins, let's take a closer look at both types.

Irreplaceable (essential)

As you already understood, these substances cannot be synthesized by the body on their own, so they must be consumed with food. The main amount of essential organic acids is found in animal proteins. When the body lacks one or another element, it begins to take it from the muscle tissue. This class consists of 8 acids. Let's get acquainted with each of them.

Leucine

This acid is responsible for the restoration and protection of muscle tissue, skin and bones. It is thanks to leucine that the growth hormone is released. In addition, this organic acid regulates blood sugar levels and promotes fat burning. It is found in meat, nuts, legumes, brown rice and wheat grains. Lecithin stimulates and therefore promotes muscle building.

Isoleucine

This acid speeds up energy production, which is why athletes love it so much. After exhausting workouts, it helps to quickly restore muscle fibers. Isoleucine relieves the so-called krepatura, takes part in the formation of hemoglobin and regulates the amount of sugar. Most isoleucine is found in meat, fish, eggs, nuts, peas and soy.

Lysine

This amino acid plays an important role in the functioning of the immune system. Its main task is the synthesis of antibodies that protect our body from the effects of viruses and allergens. In addition, lysine regulates the process of bone tissue and collagen renewal, as well as growth hormones. This organic acid can be found in foods such as: eggs, potatoes, red meat, fish and dairy products.

Phenylalanine

This alpha amino acid is responsible for the normal functioning of the central nervous system. Its deficiency in the body leads to bouts of depression and chronic diseases. Phenylalanine helps us concentrate and remember the right information. It is part of drugs used in the treatment of mental disorders, including Parkinson's disease. It has a positive effect on the functioning of the liver and pancreas. Amino acid found in: nuts, mushrooms, chicken, dairy products, bananas, apricots and Jerusalem artichoke.

Methionine

Few people know how many amino acids are in the protein, but many people know that methionine actively burns adipose tissue. But this is not all the useful properties of this acid. It affects the endurance and performance of a person. If it is not enough in the body, it can immediately be understood by the skin and nails. Methionine is found in foods such as: meat, fish, sunflower seeds, legumes, onions, garlic and dairy products.

Threonine

In an effort to find out how many amino acids are in a protein, scientists discovered a substance such as threonine, one of the last. But it is very useful for a person. Threonine is responsible for all the most important systems of the human body, namely the nervous, immune and cardiovascular systems. The first sign of its deficiency is problems with teeth and bones. Most people get threonine from dairy products, meat, mushrooms, vegetables and cereals.

tryptophan

Another important ingredient. It is responsible for the synthesis of serotonin, which is often called the feel-good hormone. Tryptophan deficiency can be detected by sleep disorders, appetite. This acid also regulates respiratory function and blood pressure. It is found mainly in: seafood, red meat, poultry, dairy products and wheat.

Valine

Performs the function of repairing damaged fibers and monitors metabolic processes in the muscles. Under heavy loads, it can have a stimulating effect. It also plays a role in human mental activity. Helps in the treatment of the liver and brain from the negative effects of alcohol and drugs. A person can get valine from: meat, mushrooms, soy, dairy, and peanuts.

It is noteworthy that 70% of all organic acids in our body are occupied by only three amino acids: leucine, isoleucine and valine. Therefore, they are considered the most important in ensuring the normal functioning of the body. In sports nutrition, they even isolated a special BCAA complex that contains precisely these three acids.

We continue to answer the question of how many major amino acids are included in the protein, and move on to the interchangeable representatives of the class.

Interchangeable

The main difference of this group is that all its representatives can be formed in the body by endogenous synthesis. The word "replaceable" misleads many. Therefore, often ignorant people say that these amino acids do not have to be consumed with food. Of course it is not! Replaceable acids, as well as essential ones, must be included in the daily diet. They can indeed be formed from other substances. But this only happens when the diet is incorrect. Then part of the useful substances and essential acids is spent on the reconstruction of non-essential acids. Therefore, it is not entirely favorable for the body. Let's analyze the essential acids included in the "major twenty".

Alanine

Helps accelerate the metabolism of carbohydrates and the removal of toxins from the liver. It is found in foods such as: meat, poultry, eggs, fish and dairy products.

Aspartic acid

It is considered a universal fuel for our body, as it significantly improves metabolism. It is found in milk, cane sugar, poultry and beef.

Asparagine

Trying to answer the question: "How many amino acids are included in the composition of the protein?", Scientists first of all discovered asparagine. It was back in 1806. This acid is involved in improving the functioning of the nervous system. It is found in all animal proteins, as well as nuts, potatoes and cereals.

Histidine

It is an important building block of all internal organs. It plays an almost key role in the formation of red and white blood cells. It has a positive effect on the immune system and sexual function. Due to the wide range of applications, histidine reserves in the body are rapidly depleted. Therefore, it is important to take it with food. Found in meat, dairy and cereal products.

Serene

Stimulates the brain and central nervous system. It is found in foods such as: meat, soy, cereals, peanuts.

Cysteine

This amino acid in the body is responsible for the synthesis of keratin. Without it, there would be no healthy nails, hair and skin. Found in foods such as: meat, eggs, red peppers, garlic, onions and broccoli.

Arginine

Speaking about how many proteinogenic amino acids are included in proteins and what functions they perform, we were convinced that each of them is important for the body. However, there are acids that, according to experts, are considered the most significant. These include arginine. It is responsible for the healthy functioning of muscles, joints, skin and liver, and also strengthens the immune system and burns fat. Arginine is often used by bodybuilders and those who wish to lose weight as part of supplements. It occurs naturally in meat, nuts, milk, cereals, and gelatin.

Glutamic acid

It is an important element for the healthy functioning of the brain and spinal cord. Often sold as a monosodium glutamate supplement. Found in eggs, meat, dairy products, fish, carrots, corn, tomatoes, and spinach.

Glutamine

Needed in protein for muscle growth and support. It is also the "fuel" of the brain. In addition, glutamine removes from the liver everything that comes there with unhealthy food. Cooking denatures the acid, so parsley and spinach need to be eaten raw to make up for it.

Glycine

Helps blood to clot and glucose to be converted into energy. It is found in meat, fish, legumes and milk.

Proline

Responsible for collagen synthesis. With a lack of proline in the body, problems with the joints begin. It is found mainly in animal proteins, therefore it is perhaps the only substance that people who do not eat meat face a lack of.

Tyrosine

Responsible for regulating blood pressure and appetite. With a lack of this acid, a person suffers from rapid fatigue. To avoid such problems, you need to eat bananas, seeds, nuts and avocados.

Foods rich in amino acids

Now you know how many amino acids are in protein. The functions and location of each of them are also known to you. Let's note the main products, using which, you can not worry about the balance of nutrition in terms of amino acids.

Eggs. They are perfectly absorbed by the body, give it a large amount of amino acids and provide protein nutrition.

Dairy. They are able to provide a person with many useful substances, the spectrum of which, by the way, is not limited to organic acids.

Meat. Perhaps the first source of protein and its constituent substances.

Fish. Rich in protein and perfectly digestible by the body.

Many are absolutely sure that without animal products it is impossible to provide the body with the proper amount of protein. This is completely false. And the proof of this is the huge number of vegetarians with excellent physical shape. Among plant foods, the main sources of amino acids are: legumes, nuts, cereals, seeds.

Conclusion

Today we learned how many amino acids are in protein. Groups of substances and a detailed description of their representatives will help you navigate the preparation of a healthy diet.

Proteins and peptides.

Squirrels- natural high-molecular nitrogen-containing organic compounds. They play a primary role in all life processes, they are carriers of life. Squirrels found in all tissues of organisms, in the blood, in the bones.


Protein, as well as carbohydrates and fats, are the most important component of human food.

Chemical structure of proteins

Protein molecules are made up of amino acid residues connected in a chain by peptide bonds.



Peptide bond occurs during the formation of proteins as a result of the interaction of the amino group ( -NH2) one amino acid with a carboxyl group ( -COOH) of another amino acid.


Two amino acids form a dipeptide (a chain of two amino acids) and a water molecule.


Dozens, hundreds and thousands of amino acid molecules combine with each other to form giant protein molecules.


Groups of atoms are repeated many times in protein molecules -CO-NH-; they are called amide, or in protein chemistry peptide groups. Accordingly, proteins are classified as natural high molecular weight polyamides or polypeptides.


The total number of naturally occurring amino acids reaches 300, but some of them are quite rare.


Among the amino acids, a group of the 20 most important is distinguished. They are found in all proteins and are called alpha amino acids.


The whole variety of proteins in most cases is formed by these twenty alpha-amino acids. At the same time, for each protein, the sequence in which the residues of its constituent amino acids are connected to each other is strictly specific. The amino acid composition of proteins is determined by the genetic code of the organism.

Proteins and peptides

And squirrels, and peptides are compounds built from amino acid residues. The differences between them are quantitative.


It is assumed that:

  • peptides contain up to 100 amino acid residues in a molecule
    (which corresponds to a molecular weight up to 10,000), and
  • squirrels- over 100 amino acid residues
    (molecular weight from 10,000 to several million).

In turn, in the group of peptides, it is customary to distinguish:

  • oligopeptides(low molecular weight peptides),
    containing in the chain no more 10 amino acid residues, and
  • polypeptides, whose chain includes up to 100 amino acid residues.

For macromolecules with the number of amino acid residues approaching or slightly exceeding 100, the concepts of polypeptides and proteins are practically not distinguished and are often synonymous.

The structure of proteins. Organization levels.


A protein molecule is an extremely complex entity. The properties of a protein depend not only on the chemical composition of its molecules, but also on other factors. For example, from the spatial structure of the molecule, from the bonds between the atoms that make up the molecule.


Allocate four levels structural organization of the protein molecule.


1. Primary structure


The primary structure is the arrangement of amino acid residues in polypeptide chains.


The sequence of amino acid residues in a chain is the most important characteristic of a protein. It is she who determines its main properties.


Each person's protein has its own unique primary structure associated with the genetic code.


2. Secondary structure.


The secondary structure is related to the spatial orientation of the polypeptide chains.


Its main types:

  • alpha Helix,
  • beta structure (looks like a folded sheet).

The secondary structure is fixed, as a rule, by hydrogen bonds between the hydrogen and oxygen atoms of the peptide groups, which are 4 units apart from each other.


Hydrogen bonds, as it were, sew the helix together, holding the polypeptide chain in a twisted state.



3. Tertiary structure


The tertiary structure reflects the spatial form of the secondary structure.


For example, a secondary structure in the form of a spiral, in turn, may have a spherical or ovoid shape.


The tertiary structure is stabilized not only by hydrogen bonds, but also by other types of interaction, such as ionic, hydrophobic, and disulfide bonds.


4. Quaternary structure


The first three levels are characteristic of the structural organization of all protein molecules.


The fourth level occurs during the formation of protein complexes consisting of several polypeptide chains.


This is a complex supramolecular formation, consisting of several proteins with their own primary, secondary and tertiary structures.


A protein with a quaternary structure can contain both identical and different polypeptide chains.


The association of polypeptide chains into a quaternary structure can lead to the emergence of new biological properties that are absent in the original proteins that form this structure.


The same types of interactions take part in the stabilization of the quaternary structure as in the stabilization of the tertiary.

Protein classification

Due to the diversity of peptides and proteins, there are several approaches to their classification. They can be classified on biological functions, composition, spatial structure.


According to their composition, proteins are divided into:

  • simple,
  • Complex.

Simple proteins.


In the hydrolysis of simple proteins, only alpha-amino acids are obtained as cleavage products.


Complex proteins.


Complex proteins, along with the actual protein part, consisting of alpha-amino acids, contain organic or inorganic parts of a non-peptide nature, called prosthetic groups.


Transport proteins are examples of complex proteins. myoglobin and hemoglobin, in which the protein part is globin- linked to a prosthetic group - heme. According to the type of prosthetic group, they are classified as hemoproteins.


Phosphoproteins contain a phosphoric acid residue, metalloproteins- metal ions.


Mixed biopolymers are also complex proteins. Depending on the nature of the prosthetic group, they are divided into:

  • Glycoproteins(contain carbohydrate part),
  • Lipoproteins(contains a lipid part),
  • Nucleoproteins(contain nucleic acids).

In the body, proteins are rarely found in a "pure" form. Basically, they are part of complex formations with a high level of organization, including other biopolymers and various organic and inorganic groups as subunits.


According to the spatial structure, proteins are divided into two large classes:

  • Globular and
  • fibrillar.

globular proteins.


For globular proteins, an alpha-helical structure is more characteristic, and their chains are bent in space so that the macromolecule takes the form of a sphere.


Globular proteins dissolve in water and saline solutions with the formation of colloidal systems.


Examples of globular proteins − albumen(egg whites) globin(protein portion of hemoglobin) myoglobin almost all enzymes.


fibrillar proteins.


For fibrillar proteins more typical beta structure. As a rule, they have a fibrous structure, do not dissolve in water and saline solutions.


These include many widely distributed proteins - beta keratin(hair, horn tissue), beta fibroin(silk), myoinosine(muscle tissue) collagen(connective tissue).

Functions of proteins in the body.

The classification of proteins according to their functions is rather arbitrary, since the same protein can perform several functions.


Below are the main functions of proteins in the body:


1. Catalytic function.


The proteins in this group are called enzymes. Enzymes catalyze various chemical reactions. For example, the reactions of splitting complex molecules (catabolism) and their synthesis (anabolism).


Examples of catalytic proteins: catalase, alcohol dehydrogenase, pepsin, trypsin, amylase etc.


2. Structural function


Give shape to the cell and its organelles. For example, monomers actin and tubulin form long filaments that make up the cytoskeleton, allowing the cell to maintain its shape. Collagen and elastin- the main components of the intercellular substance of the connective tissue (for example, cartilage), and from another structural protein keratin consists of hair, nails, bird feathers and some shells.


3. Protective function


There are several types of protective functions of proteins:

  • Physical protection
    Provide physical protection to the body collagen- protein that forms the backbone
    intercellular substance of connective tissues (including bones, cartilage,
    tendons and deep layers of the skin (dermis)); keratin, which forms the basis of horny
    shields, hair, feathers, horns, and other derivatives of the epidermis. Typically these proteins
    considered as proteins with structural function. Examples of proteins of this group
    serve fibrinogens and thrombins involved in blood clotting.

  • Chemical protection
    The binding of toxins to protein molecules can provide their detoxification.
    A particularly important role in detoxification in humans is played by liver enzymes,
    splitting poisons or converting them into a soluble form, which contributes to their
    rapid elimination from the body.

  • immune protection
    Proteins that make up blood and other body fluids are involved in
    the body's defense response to both injury and attack by pathogens. They are
    neutralize bacteria, viruses or foreign proteins.

4. Regulatory function


Proteins of this group regulate various processes occurring in cells or in the body. The proteins in this group include: protein hormones, receptor proteins etc.


Hormones are carried in the blood. Most animal hormones are proteins or peptides. Hormones regulate the concentration of substances in the blood and cells, growth, reproduction and other processes. An example of such proteins is insulin, which regulates the concentration of glucose in the blood.


5. Alarm function


Signaling function of proteins- the ability of proteins to serve as signaling substances, transmitting signals between cells, tissues, organs and organisms. The signaling function is often combined with the regulatory function, since many intracellular regulatory proteins also carry out signal transduction.


The signaling function is performed hormone proteins, cytokines, growth factors and others. The binding of a hormone to its receptor is a signal that triggers a cell response.


Cells interact with each other using signal proteins transmitted through the intercellular substance. Such proteins include, for example, cytokines and growth factors.


6. Transport function


The participation of proteins in the transfer of substances into and out of cells, in their movements within cells, as well as in their transport by blood and other fluids throughout the body.


An example of a transport protein is hemoglobin, which carries oxygen from the lungs to other tissues and carbon dioxide from tissues to the lungs, as well as proteins homologous to it, found in all kingdoms of living organisms.


Some membrane proteins are involved in the transport of small molecules through the cell membrane, changing its permeability.

7. Spare (backup) function


These proteins include the so-called reserve proteins, which are stored as a source of energy and matter in plant seeds (for example, globulins 7S and 11S) and animal eggs. A number of other proteins are used in the body as a source of amino acids. Examples of storage proteins are casein, egg albumin.


8. Receptor function


Protein receptors can be located both in the cytoplasm and embedded in the cell membrane.


Receptors react by changing their spatial configuration to the attachment of a molecule of a certain chemical substance to it, which transmits an external regulatory signal and, in turn, transmits this signal inside the cell or cell organelle.


9. Motor (motor) function


Motor protein, motor protein - a class of molecular motors that can move. They transform the chemical energy contained in ATP, into mechanical energy of motion.


Motor proteins provide movement of the body, such as muscle contraction.


Motor proteins include proteins of the cytoskeleton - dyneins, kinesins, as well as proteins involved in muscle contractions - actin, myosin.

Among the organic compounds of a cell, proteins are the most important. The content of proteins in the cell ranges from 50% to 80%.

Squirrels- These are high-molecular organic compounds that consist of carbon, hydrogen, oxygen, sulfur and nitrogen. Some proteins contain phosphorus and metal cations.

Proteins are biopolymers that are made up of amino acid monomers. Their molecular weight varies from several thousand to several million, depending on the number of amino acid residues.

Proteins contain only 20 types of amino acids out of 170 found in living organisms.

Amino acids(see Fig. 1) - organic compounds in the molecules of which an amino group () with basic properties and a carboxyl group () with acidic properties are simultaneously present. The part of the molecule called the radical ( R), different amino acids have different structures.

Rice. 1. Amino acid

Depending on the radical, amino acids are divided into (see Fig. 2):

1. acidic (carboxyl group in the radical);

2. basic (amino group in the radical);

3. neutral (do not have charged radicals).

Rice. 2. Classification of amino acids

Amino acids are connected to each other through a peptide bond. This bond is formed by separating a water molecule from the interaction of the amino group of one amino acid with the carboxyl group of another amino acid. A reaction that releases water is called condensation reaction, and the emerging covalent nitrogen-carbon bond - peptide bond.

Rice. 3. Dipeptide

Compounds formed by the condensation of two amino acids are dipeptide(see Fig. 3). At one end of its molecule is an amino group, and at the other - a free carboxyl group. Due to this, the dipeptide can attach other molecules to itself. If many amino acids combine in this way, then polypeptide(see Fig. 4).

Rice. 4. Polypeptide

Polypeptide chains are very long and can be composed of various amino acids. A protein molecule can include either one polypeptide chain or several such chains.

Many animals, including humans, unlike bacteria and plants, cannot synthesize all the amino acids that make up protein molecules. That is, there are a number of essential amino acids that must come from food.

Essential amino acids include: lysine, valine, leucine, isoleucine, threonine, phenylalanine, tryptophan, tyrosine, methionine.

More than two hundred thousand tons of amino acids are produced annually in the world, which are used in practical human activities. They are used in medicine, perfumery, cosmetics, agriculture.

To a greater extent, they produce glutamic acid and lysine, as well as glycine and methionine.

Appointment of amino acids

1. Glutamic acid

It is used in psychiatry (for epilepsy, for the treatment of dementia and the consequences of birth injuries), in the complex therapy of peptic ulcer and for hypoxia. It also improves the taste of meat products.

2. Aspartic acid

Aspartic acid increases the oxygen consumption of the heart muscle. In cardiology, Panangin is used - a drug containing potassium aspartate and magnesium aspartate. Panangin is used to treat various kinds of arrhythmias, as well as coronary heart disease.

3. Methionine

Protects the body in case of poisoning by bacterial endotoxins and some other poisons, therefore it is used to protect the body from environmental toxicants. It has radioprotective properties.

4. Glycine

It is an inhibitory mediator in the central nervous system. Used as a sedative, used in the treatment of chronic alcoholism.

5. Lysine

The main food and feed additive. Used as antioxidants in the food industry (prevents food spoilage).

The difference between proteins and peptides is the number of amino acid residues. There are more than 50 of them in proteins, and less than 50 in peptides.

Currently, several hundred different peptides have been isolated that perform an independent physiological role in the body.

Peptides include:

1. Peptide antibiotics (gramicidin S).

2. Regulatory peptides - substances that regulate many chemical reactions in the cells and tissues of the body. These include: peptide hormones (insulin), oxytocin, which stimulates the contraction of smooth muscles.

3. Neuropeptides.

Depending on the structure, simple and complex proteins are distinguished.

1. Simple proteins consist only of the protein part.

2. Complex have a non-protein part.

If a carbohydrate is used as a non-protein part, then this glycoproteins.

If lipids are used as the non-protein part, then this lipoproteins.

If nucleic acids are used as a non-protein part, then this nucleoproteins.

Proteins have 4 main structures: primary, secondary, tertiary, quaternary (see Figure 5).

Rice. 5. Protein structure

1. Under primary structure understand the sequence of amino acid residues in a polypeptide chain. It is unique to any protein and determines its shape, properties and functions.

A significant coincidence of the primary structure is characteristic of proteins that perform similar functions. Changing just one amino acid in one of the chains can change the function of a protein molecule. For example, replacing glutamic acid with valine results in abnormal hemoglobin production and a disease called sickle cell anemia.

2. secondary structure- ordered folding of the polypeptide chain into a spiral (looks like a stretched spring). The coils of the helix are strengthened by hydrogen bonds between carboxyl groups and amino groups. Almost all CO and NH groups take part in the formation of hydrogen bonds.

3. Tertiary structure- packing of polypeptide chains into globules, resulting from the occurrence of chemical bonds (hydrogen, ionic, disulfide) and the establishment of hydrophobic interactions between radicals of amino acid residues.

4. Quaternary structure characteristic of complex proteins, the molecules of which are formed by two or more globules.

The loss of a protein molecule of its natural structure is called denaturation. It can occur when exposed to temperature, chemicals, heating and irradiation.

If primary structures are not disturbed during denaturation, then when normal conditions are restored, the protein is able to recreate its structure. This process is called renaturation(see Fig. 6). Consequently, all structural features of the protein are determined by the primary structure.

Rice. 6. Denaturation and renaturation

Sickle cell anemia is an inherited disease in which red blood cells that carry oxygen do not look like a disk, but take on the shape of a sickle (see Figure 7). The immediate cause of the change in shape is a slight change in the chemical structure of hemoglobin (the main component of the red blood cell).

Rice. 7. Appearance of a normal and sickle-shaped erythrocyte

Symptoms: disability, constant shortness of breath, palpitations, reduced immunity.

One of the signs of sickle cell anemia is the yellowness of the skin.

There are various forms of the disease. In the most severe form, a person experiences developmental delay, such people do not live up to adolescence.

Bibliography

  1. Kamensky A.A., Kriksunov E.A., Pasechnik V.V. General biology 10-11 class Bustard, 2005.
  2. Biology. Grade 10. General biology. Basic level / P.V. Izhevsky, O.A. Kornilova, T.E. Loshchilin and others - 2nd ed., revised. - Ventana-Graf, 2010. - 224 pages.
  3. Belyaev D.K. Biology 10-11 class. General biology. A basic level of. - 11th ed., stereotype. - M.: Education, 2012. - 304 p.
  4. Agafonova I.B., Zakharova E.T., Sivoglazov V.I. Biology 10-11 class. General biology. A basic level of. - 6th ed., add. - Bustard, 2010. - 384 p.
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Homework

  1. Questions 1-6 at the end of paragraph 11 (p. 46) - Kamensky A.A., Kriksunov E.A., Pasechnik V.V. "General biology", grade 10-11 ()
  2. What functional groups are in amino acids?

Squirrels- high-molecular organic compounds, consisting of residues of α-amino acids.

AT protein composition includes carbon, hydrogen, nitrogen, oxygen, sulfur. Some proteins form complexes with other molecules containing phosphorus, iron, zinc and copper.

Proteins have a large molecular weight: egg albumin - 36,000, hemoglobin - 152,000, myosin - 500,000. For comparison: the molecular weight of alcohol is 46, acetic acid - 60, benzene - 78.

Amino acid composition of proteins

Squirrels- non-periodic polymers, the monomers of which are α-amino acids. Usually, 20 types of α-amino acids are called protein monomers, although more than 170 of them have been found in cells and tissues.

Depending on whether amino acids can be synthesized in the body of humans and other animals, there are: non-essential amino acids- can be synthesized essential amino acids- cannot be synthesized. Essential amino acids must be ingested with food. Plants synthesize all kinds of amino acids.

Depending on the amino acid composition, proteins are: complete- contain the entire set of amino acids; defective- some amino acids are absent in their composition. If proteins are made up of only amino acids, they are called simple. If proteins contain, in addition to amino acids, also a non-amino acid component (a prosthetic group), they are called complex. The prosthetic group can be represented by metals (metalloproteins), carbohydrates (glycoproteins), lipids (lipoproteins), nucleic acids (nucleoproteins).

All amino acids contain: 1) a carboxyl group (-COOH), 2) an amino group (-NH 2), 3) a radical or R-group (the rest of the molecule). The structure of the radical in different types of amino acids is different. Depending on the number of amino groups and carboxyl groups that make up amino acids, there are: neutral amino acids having one carboxyl group and one amino group; basic amino acids having more than one amino group; acidic amino acids having more than one carboxyl group.

Amino acids are amphoteric compounds, since in solution they can act as both acids and bases. In aqueous solutions, amino acids exist in different ionic forms.

Peptide bond

Peptides- organic substances consisting of amino acid residues connected by a peptide bond.

The formation of peptides occurs as a result of the condensation reaction of amino acids. When the amino group of one amino acid interacts with the carboxyl group of another, a covalent nitrogen-carbon bond arises between them, which is called peptide. Depending on the number of amino acid residues that make up the peptide, there are dipeptides, tripeptides, tetrapeptides etc. The formation of a peptide bond can be repeated many times. This leads to the formation polypeptides. At one end of the peptide there is a free amino group (it is called the N-terminus), and at the other end there is a free carboxyl group (it is called the C-terminus).

Spatial organization of protein molecules

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 expanded form, in the form of a chain, therefore, polypeptide chains are folded, acquiring a certain three-dimensional structure, or conformation. Allocate 4 levels spatial organization of proteins.

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

If a protein molecule consists of only 10 amino acid residues, then the number of theoretically possible variants of protein molecules that differ in the order of alternation of amino acids is 10 20 . With 20 amino acids, you can make even more diverse combinations of 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.

It is the primary structure of the protein molecule that determines the properties of the protein molecules and its spatial configuration. The replacement of just one amino acid for another in the polypeptide chain leads to a change in the properties and functions of the protein. For example, the replacement of 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 a stretched spring). The coils of the helix are strengthened by hydrogen bonds 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, repeating many times, they impart stability and rigidity to this configuration. At the level of the secondary structure, there are proteins: fibroin (silk, web), keratin (hair, nails), collagen (tendons).

Tertiary structure- packing of polypeptide chains into globules, resulting from the occurrence 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 tend to appear on the surface of the molecule as a result of hydration (interaction with water dipoles). In some proteins, the tertiary structure is stabilized by disulfide covalent bonds that form between the sulfur atoms of the two cysteine ​​residues. At the level of the tertiary structure, there are enzymes, antibodies, some hormones.

Quaternary structure characteristic of complex proteins, the molecules of which are formed by two or more globules. 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). Each subunit is associated with 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 an abnormal conformation of prions, the surface proteins of nerve cells.

Protein Properties

The amino acid composition, the structure of the protein molecule determine its properties. Proteins combine basic and acidic properties determined by amino acid radicals: the more acidic amino acids in a protein, the more pronounced its acidic properties. The ability to give and attach H + determine buffer properties of proteins; one of the most powerful buffers is hemoglobin in erythrocytes, which maintains the pH of the blood at a constant level. There are soluble proteins (fibrinogen), there are insoluble proteins that perform mechanical functions (fibroin, keratin, collagen). There are chemically active proteins (enzymes), there are chemically inactive, resistant to various environmental conditions and extremely unstable.

External factors (heat, ultraviolet radiation, heavy metals and their salts, pH changes, radiation, dehydration)

can cause a violation of the structural organization of the protein molecule. The process of losing the three-dimensional conformation inherent in a given protein molecule is called denaturation. The cause of denaturation is the breaking of bonds that stabilize a particular protein structure. Initially, the weakest ties are torn, and when conditions become tougher, even stronger ones. Therefore, first the quaternary, then the tertiary and secondary structures are lost. A change in the spatial configuration leads to a change in the properties of the protein and, as a result, makes it impossible for the protein to perform its biological functions. If denaturation is not accompanied by the destruction of the primary structure, then it can be reversible, in this case, self-healing of the conformation characteristic of the protein occurs. Such denaturation is subjected, for example, to membrane receptor proteins. The process of restoring the structure of a protein after denaturation is called renaturation. If the restoration of the spatial configuration of the protein is impossible, then denaturation is called irreversible.

Functions of proteins

Function Examples and explanations
Construction Proteins are involved in the formation of cellular and extracellular structures: they are part of cell membranes (lipoproteins, glycoproteins), hair (keratin), tendons (collagen), etc.
Transport The blood protein hemoglobin attaches oxygen and transports it from the lungs to all tissues and organs, and from them carbon dioxide transfers to the lungs; The composition of cell membranes includes special proteins that provide an active and strictly selective transfer of certain substances and ions from the cell to the external environment and vice versa.
Regulatory Protein hormones are involved in the regulation of metabolic processes. For example, the hormone insulin regulates blood glucose levels, promotes glycogen synthesis, and increases the formation of fats from carbohydrates.
Protective In response to the penetration of foreign proteins or microorganisms (antigens) into the body, special proteins are formed - antibodies that can bind and neutralize them. Fibrin, formed from fibrinogen, helps to stop bleeding.
Motor The contractile proteins actin and myosin provide muscle contraction in multicellular animals.
Signal Molecules of proteins are embedded in the surface membrane of the cell, capable of changing their tertiary structure in response to the action of environmental factors, thus receiving signals from the external environment and transmitting commands to the cell.
Reserve In the body of animals, proteins, as a rule, are not stored, with the exception of egg albumin, milk casein. But thanks to proteins in the body, some substances can be stored in reserve, for example, during the breakdown of hemoglobin, iron is not excreted from the body, but is stored, forming a complex with the ferritin protein.
Energy With the breakdown of 1 g of protein to the final products, 17.6 kJ is released. First, proteins break down into amino acids, and then to the end products - water, carbon dioxide and ammonia. However, proteins are used as an energy source only when other sources (carbohydrates and fats) are used up.
catalytic One of the most important functions of proteins. Provided with proteins - enzymes that accelerate the biochemical reactions that occur in cells. For example, ribulose biphosphate carboxylase catalyzes CO2 fixation during photosynthesis.

Enzymes

Enzymes, or enzymes, is a special class of proteins that are biological catalysts. Thanks to enzymes, biochemical reactions proceed at a tremendous speed. The rate of enzymatic reactions is tens of thousands of times (and sometimes millions) higher than the rate of reactions involving inorganic catalysts. The substance on which an enzyme acts is called substrate.

Enzymes are globular proteins structural features Enzymes can be divided into two groups: simple and complex. simple enzymes are simple proteins, i.e. consist only of amino acids. Complex enzymes are complex proteins, i.e. in addition to the protein part, they include a group of non-protein nature - cofactor. For some enzymes, vitamins act as cofactors. In the enzyme molecule, a special part is isolated, called the active center. active center- a small section of the enzyme (from three to twelve amino acid residues), where the binding of the substrate or substrates occurs with the formation of the enzyme-substrate complex. Upon completion of the reaction, the enzyme-substrate complex decomposes into an enzyme and a reaction product(s). Some enzymes have (other than active) allosteric centers- sites to which regulators of the rate of enzyme work are attached ( allosteric enzymes).

Enzymatic catalysis reactions are characterized by: 1) high efficiency, 2) strict selectivity and direction of action, 3) substrate specificity, 4) fine and precise regulation. The substrate and reaction specificity of enzymatic catalysis reactions is explained by the hypotheses of E. Fischer (1890) and D. Koshland (1959).

E. Fisher (key-lock hypothesis) suggested that the spatial configurations of the active site of the enzyme and the substrate should correspond exactly to each other. The substrate is compared to the "key", the enzyme - to the "lock".

D. Koshland (hypothesis "hand-glove") suggested that the spatial correspondence between the structure of the substrate and the active center of the enzyme is created only at the moment of their interaction with each other. This hypothesis is also called induced fit hypothesis.

The rate of enzymatic reactions depends on: 1) temperature, 2) enzyme concentration, 3) substrate concentration, 4) pH. It should be emphasized that since enzymes are proteins, their activity is highest under physiologically normal conditions.

Most enzymes can only work at temperatures between 0 and 40°C. Within these limits, the reaction rate increases by about 2 times for every 10 °C rise in temperature. At temperatures above 40 °C, the protein undergoes denaturation and the activity of the enzyme decreases. At temperatures close to freezing, the enzymes are inactivated.

With an increase in the amount of substrate, the rate of the enzymatic reaction increases until the number of substrate molecules becomes equal to the number of enzyme molecules. With a further increase in the amount of substrate, the rate will not increase, since the active sites of the enzyme are saturated. An increase in the enzyme concentration leads to an increase in catalytic activity, since a larger number of substrate molecules undergo transformations per unit time.

For each enzyme, there is an optimal pH value at which it exhibits maximum activity (pepsin - 2.0, salivary amylase - 6.8, pancreatic lipase - 9.0). At higher or lower pH values, the activity of the enzyme decreases. With sharp shifts in pH, the enzyme denatures.

The speed of allosteric enzymes is regulated by substances that attach to allosteric centers. If these substances speed up the reaction, they are called activators if they slow down - inhibitors.

Enzyme classification

According to the type of catalyzed chemical transformations, enzymes are divided into 6 classes:

  1. oxidoreductase(transfer of hydrogen, oxygen or electron atoms from one substance to another - dehydrogenase),
  2. transferase(transfer of a methyl, acyl, phosphate or amino group from one substance to another - transaminase),
  3. hydrolases(hydrolysis reactions in which two products are formed from the substrate - amylase, lipase),
  4. lyases(non-hydrolytic addition to the substrate or the elimination of a group of atoms from it, while C-C, C-N, C-O, C-S bonds can be broken - decarboxylase),
  5. isomerase(intramolecular rearrangement - isomerase),
  6. ligases(the connection of two molecules as a result of the formation of C-C, C-N, C-O, C-S bonds - synthetase).

Classes are in turn subdivided into subclasses and subsubclasses. In the current international classification, each enzyme has a specific code, consisting of four numbers separated by dots. The first number is the class, the second is the subclass, the third is the subclass, the fourth is the serial number of the enzyme in this subclass, for example, the arginase code is 3.5.3.1.

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There are only 20 basic amino acids. Their names are associated with random moments. All amino acids that are part of natural proteins are α-amino acids. This means that the amino and carboxyl groups are on the same carbon atom.

1. aminoacetic acid (glycine);

2. α-aminopropanoic acid (alanine);

3. α-aminopentanoic acid (valine);

4. α-aminoisocaproic acid (leucine);

5. α-amino-β-methylvaleric acid (isoleucine);

6. α-amino-β-hydroxypropanoic acid (serine);

7. α-amino-β-hydroxybutyric acid (threonine);

Sulfur-containing:

8. α-amino-β-mercaptopropanoic acid (cysteine);

9. α-amino-γ-methylthiobutyric acid (methionine);

10. α-aminosuccinic acid (aspartic acid);

11. aspartic acid amide (asparagine);

12. α-aminoglutaric acid (glutamic acid);

13. α-aminoglutaric acid amide (gutamine);

14. α, ε-diaminocaproic acid (leucine);

15. α-amino-δ-guanidylovaleric acid

(arginine);

Cyclic :

16. α-amino-β-phenylpropanoic acid (phenylalanine);

17. α-amino-β-para-hydroxyphenylproanoic acid (tyrosine);

18. α-amino-β-imidozolylpropanoic acid (histedine);

19. α-amino-β-indolylpropanoic acid (tryptophan);

20. α-tetrahydropyrolecarboxylic acid (proline).

All natural amino acids belong to the L-stereochemical series, D-series only as an exception in bacteria, as part of capsules to protect bacteria from the action of enzymes.

Lecture 3.

Each amino acid has its own unique physical and chemical properties - the isoelectric point, i.e. the pH of the medium at which the solution of this amino acid is electrically neutral. (q = 0).

If we consider such an acid in an aqueous medium, then dissociation occurs both in the acidic and in the basic type - a bipolar ion.

In the body of mammals, the liver contains the enzyme D-amino acid oxidase, which selectively destroys D-amino acids that come from food. D-amino acids have been found in some peptides of microorganisms. In addition, D-amino acids are part of a large number of antibiotics. For example, D-valine, D-leucine are part of the antibiotic borderidin, D-phenylalanine is part of borderidin-C, penicillin contains an unusual fragment D-dimethylcysteine.



The process of racimization (transition of D to L) does not occur enzymatically, therefore it is very slow. This is the basis for determining the age of mammals.

All amino acids have in their composition an amino and a carboxyl group, they have the properties of amines and carboxylic acids. In addition, α-amino acids are characterized ninhydrin reaction(common with proteins). With an alcohol solution of ninhydrin, a blue-violet color very quickly appears, with yellow propyne.

At the end of the 19th century, there was a controversy about how amino acids form a bond; if you take two amino acids and merge them together, you will never get a linear structure (due to thermodynamics, cyclization occurs). It was not possible to obtain a polypeptide in the 19th century.

Linear molecules won't work. From the point of view of thermodynamics, it is more advantageous to split off 2H 2 O than to form a linear molecule.

In 1888, the chemist Danilevsky suggested that proteins are polypeptides, linear molecules that are formed as a result of the action of the carboxyl group of one amino acid with the carboxyl group of another amino acid with the elimination of water and a dipeptide is formed:

An amide bond is formed (for proteins, a peptide bond), these peptide bonds are separated by only one carbon atom. Based biuret reaction Danilevsky made such a conclusion. This is the reaction of a protein solution with copper sulfate in an alkaline medium, a blue-violet color is formed, a chilate complex with copper ions is formed, as a result of the fact that the peptide bond in protein molecules has a specific structure. Due to keto-enol tautomerism, it is half double, half single. Typical reaction with Cu(OH) 2:

The biuret reaction is typical for biuret (Fig. 1), for malonamide (Fig. 2), proteins.

In order to finally prove that whites are polypeptides in 1901, Fischer synthesized a polypeptide, independently of him Hoffmann also synthesized a polypeptide:

Synthesis of a polypeptide according to Fischer:

The product gave a biuret reaction, was poorly soluble, had no biological activity, was cleaved by protolytic enzymes, and enzymes are specific biocatalysts that break down natural proteins, which means that this product has the same structure as natural proteins.

Currently, more than 2 thousand different proteins have been synthesized. The main thing in protein synthesis is the protection of the amino group and the activation of the carboxyl group so that the synthesis is directed. Amino groups are protected by acylation, for this they are treated with trichloroacetic acid anhydrides and a trifluoroacyl group is introduced, or treated according to Zeners (benzyl ester of chlorocarbonic acid).

For the synthesis of each particular polypeptide, for stitching a particular site can be carried out their own methods.

Protection by Zerves, activation by Curtius, unprotection by Beckman :

Solid-phase synthesis of polypeptides and proteins, a specific feature of polypeptide synthesis is a huge number of operations of the same type. A method has been developed by Robert Maryfilod . Monomers are amino acids that are used for synthesis, containing a protected amino group and activated carboxyl groups - synthons. Merifield proposed: to fix the first monomer on a polymer resin (insoluble carrier) and all subsequent operations are carried out with a polypeptide growing on a polymer base, the next synthon and a reagent are added alternately to the resin to remove the terminal protective group. The chemical steps are punctuated by appropriate washes. Throughout the process, the polypeptide remains bound to the resin. This process can be easily automated by programming the change of flows through the column. Synthesizers are currently being developed. At the final stage of synthesis, the polypeptide is covalently bound to the resin, removed from this resin, and the protective group is removed. One of the biggest problems in solid phase synthesis is the racimization of amino acids during synthesis. This is especially dangerous in this synthesis, as There are no intermediate steps for isolating racimates. There are no methods of secession at the moment, but there are conditions for rationalization to be as small as possible. Merifield himself obtained several polypeptides by this method at once, bradykidin was obtained - a hormone with a vasodilating effect, angiotensin - a hormone that increases blood pressure, the enzyme ribonuclease, which catalyzes the hydrolysis of RNA.

The yield of products by this method is not significantly comparable with the methods that have been used before. With the help of automation, this method can be used on an industrial scale.

Each polypeptide has an N-terminus and another C-terminus. The amino acid that takes part changes the ending to il

Glycyl-valyl-tyrosyl-histedine-asparagyl-proline. To determine the amino acids in the polypeptide, it is necessary to carry out hydrolysis, it is carried out at 100 C for 24 hours with 6N hydrochloric acid. Further, the hydrolysis products are analyzed - separated by ion-exchange chromatography on a column of sulfonated polystyrene. Then washed with citrate buffer from the column. By the amount of eluent, it is judged which acids, i.e. acidic acids will be washed out first, and basic acids will be washed out last. In this way, it is possible to determine at what point which amino acid has passed, and the amount is determined photometrically using nindrin, this method can determine 1 μg. If it is necessary to determine 1 ng, fluoroscanin is used, it reacts with α-amino acids, forming a highly fluorescent compound. They determine which and how many amino acids are located, but the sequence of amino acids cannot be determined.

Fluoroslanin: