Proteins as biopolymers. Properties and biological functions of proteins
Protein substances or proteins also belong to natural IUDs. They are high-molecular organic compounds, the complex molecules of which are built from amino acids. The molecular weight of proteins ranges from 27,000 to 7 million. When dissolved in water, proteins form true solutions. In water, protein molecules dissociate into ions. This dissociation can be acidic or basic, depending on the pH of the medium. In a strongly acidic environment, the protein behaves like a base, its molecule dissociates due to NH2 groups according to the main type:
HONH3-R-COOH++OH-
Acid dissociation is suppressed in this case.
In an alkaline medium, on the contrary, the main dissociation is suppressed, and predominantly acid dissociation occurs.
HONH3 - R - COOH - + H+
However, at a certain pH value, the degree of dissociation of amino and carboxyl groups acquires the same values when protein molecules become electrically neutral. The pH value at which a protein molecule is in an electrically neutral state is called the isoelectric point, abbreviated IEP. For most proteins, the IEP lies in the region of acidic solutions. In particular, for gelatin - 4.7; milk casein - 4.6; g-globulin blood - 6.4; pepsin - 2.0; chymotrypsin - 8.0; egg albumin - 4.7; pharmacogel A - 7.0; pharmagel B - 4.7. It is necessary to know the isoelectric point, since it has been established that the stability of protein solutions in IE will be minimal (the manifestation of all its properties will be minimal). In some cases, it is even possible for proteins to precipitate. This is due to the fact that in IE along the entire length of the protein molecule there is an equal number of positively and negatively charged ionogenic groups, which leads to a change in the configuration of the molecule. A flexible molecule curls up into a tight ball due to the attraction of unlike ions.
The change in the viscosity of solutions is associated with a change in the shape of macromolecules.
Representatives of this group of natural IUDs are such enzymes, in particular:
Pepsin is obtained by special treatment of the mucous membranes of the stomach of pigs and mixed with powdered sugar. It is a white, slightly yellowish powder of sweet taste with a slight peculiar smell. It is used for digestive disorders (achilia, gastritis, dyspepsia, etc.).
Trypsin is obtained from the pancreas of cattle. This is a protein with a molecular weight of 21000. It can be in two polymorphic forms: crystalline and amorphous. Trypsin crystalline is applied externally in eye drops; at a concentration of 0.2-0.25% for purulent wounds, bedsores, necrosis for parenteral (intramuscular) use. It is a white crystalline powder, odorless, easily soluble in water, isotonic sodium chloride solution.
Chymotrypsin - a mixture of chymopsin and trypsin, recommended only for topical application in water 0.05-0.1-1% solutions for purulent wounds, burns.
Hydrolysin - obtained by hydrolysis of the blood of animals, is part of anti-shock liquids.
Aminopeptide - is also obtained by hydrolysis of the blood of animals, is used to feed depleted organisms. It is used intravenously, and the rectal route of administration is also recommended.
Collagen is the main protein of connective tissue, it consists of macromolecules with a three-helix structure. The main source of collagen is the skin of cattle, which contains up to 95% of it. Collagen is obtained by alkaline-salt treatment of split wood.
Collagen is used to cover wounds in the form of films with furacilin, boric acid, sea buckthorn oil, methyluracil, and also in the form of eye films with antibiotics. Hemostatic sponges with various medicinal substances are used. Collagen provides optimal activity of medicinal substances, which is associated with deep penetration and prolonged contact of medicinal substances included in the collagen base with body tissues.
The combination of biological properties of collagen (lack of toxicity, complete resorption and utilization in the body, stimulation of reparative processes) and its technological properties make it possible to widely use dosage forms in technology.
All these protein substances are highly soluble in water. They are unlimited swelling IUDs, which is explained by the structure of their macromolecules. The macromolecules of these substances are rolled spherical globules. The bonds between molecules are small, they are easily solvated and pass into solutions. Low-viscosity solutions are formed.
Medical gelatin also belongs to the group of proteins, the description of this substance is given in SP IX on page 309. It is a product of partial hydrolysis of collagen and casein contained in the bones, skin and cartilage of animals. It is a colorless or slightly yellowish translucent flexible leaves or small odorless plates.
It is used orally to increase blood clotting and stop gastrointestinal bleeding. 10% solutions of gelatin are used for injections. Solutions of gelatin in water and glycerin are used for the preparation of ointments and suppositories. Gelatin molecules have a linear elongated shape (fibrillar). Gelatin is a protein, a condensation product of amino acids, its molecules contain many polar groups (carboxyl and amino groups), which have a great affinity for water, therefore gelatin forms true solutions in water. At room temperature 20-25?C, it swells to a limited extent, and dissolves with increasing temperature.
Gelatose is a hydrolysis product of gelatin. It is a slightly yellowish hygroscopic powder. Used to stabilize heterogeneous systems (suspensions and emulsions). Sparingly soluble in water.
Farmagel A and B are gelatin hydrolysis products that differ in isoelectric points. Farmagel A has at pH - 7.0 IET, farmagel B - at pH 4.7. They are used as stabilizers in heterogeneous systems. Disadvantages of gelatin, gelatose and pharmacogels: their solutions are rapidly subject to microbial spoilage.
Of the proteins, lecithin is also used as an emulsifier. It is found in egg white. It has good emulsifying properties and can be used to stabilize injectable dosage forms.
Lesson topic: Proteins are natural polymers. The composition and structure of proteinsGoals:
Tutorial: form a holistic view of biopolymers -
proteins based on the integration of chemistry and biology courses. Introduce students to the composition, structure, properties and functions of proteins. Use experiments with proteins to implement interdisciplinary connections and to develop the cognitive interest of students.
Developing: develop cognitive interest in subjects, the ability to reason logically, apply knowledge in practice.
Nurturing: to develop skills of joint activity, to form the ability for self-esteem.
Lesson type: learning new knowledge.
DURING THE CLASSES
Organizing time.
Greeting, mark absent. Presentation of the topic of the lesson and the purpose of the lesson.
Actualization of attention
Modern science presents the process of life as follows:
"Life is an interweaving of the most complex chemical processes of the interaction of proteins between themselves and other substances."
“Life is a way of existence of protein bodies”
F.Engels
Today we will look at proteins from a biological and chemical point of view.
Learning new material.
1. The concept of proteins
Protein is muscles, connective tissues (tendons, ligaments, cartilage). Protein molecules are incorporated into bone tissue. Hair, nails, teeth, and skin are woven from special forms of protein. From protein molecules, separate very important hormones are formed, on which health depends. Most enzymes also include protein fragments, and the quality and intensity of physiological and biochemical processes occurring in the body depend on enzymes.
The content of proteins in various human tissues is not the same. So, muscles contain up to 80% protein, spleen, blood, lungs - 72%, skin - 63%, liver - 57%, brain - 15%, adipose tissue, bone and dental tissue - 14-28%.
Proteins are high-molecular natural polymers built from amino acid residues connected by an amide (peptide) bond -CO-NH-. Each protein is characterized by a specific amino acid sequence and individual spatial structure. Proteins account for at least 50% of the dry mass of organic compounds in an animal cell.
2. Composition and structure of proteins.
The composition of protein substances includes carbon, hydrogen, oxygen, nitrogen, sulfur, phosphorus.
Hemoglobin - C 3032 H 4816 O 872 N 780 S 8 Fe 4 .
The molecular weight of proteins ranges from several thousand to several million. Mr egg protein = 36,000, Mr muscle protein = 1,500,000.
To establish the chemical composition of protein molecules, their structure was helped by the study of the products of protein hydrolysis.
In 1903, the German scientist Emil Hermann Fischer proposed the peptide theory, which became the key to the mystery of protein structure. Fisher suggested that proteins are polymers of amino acid residues connected by a NH-CO peptide bond. The idea that proteins are polymeric formations was expressed as early as 1888 by the Russian scientist Alexander Yakovlevich Danilevsky.
3. Definition and classification of proteins
Proteins are natural high-molecular natural compounds (biopolymers) built from alpha-amino acids connected by a special peptide bond. The composition of proteins includes 20 different amino acids, hence the huge variety of proteins with various combinations of amino acids. As from 33 letters of the alphabet we can make an infinite number of words, so from 20 amino acids - an infinite number of proteins. There are up to 100,000 proteins in the human body.
The number of amino acid residues included in the molecules is different: insulin - 51, myoglobin - 140. Hence, M r of the protein is from 10,000 to several million.
Proteins are divided into proteins (simple proteins) and proteids (complex proteins).
4. Structure of proteins
A strictly defined sequence of amino acid residues in a polypeptide chain is called the primary structure. It is often referred to as a linear chain. This structure is characteristic of a limited number of proteins.
Studies have shown that some parts of the polypeptide chain are folded into a spiral due to hydrogen bonds between groups - CO and - NH. This is how the secondary structure is formed.
The helical polypeptide chain must somehow be folded, compacted. In the packed state, protein molecules have an ellipsoidal shape, which is often called a coil. This is a tertiary structure formed by hydrophobic. Ester bonds, some proteins have S–S bonds (bisulfide bonds)
The highest organization of protein molecules is the quaternary structure - protein macromolecules connected to each other, forming a complex.
Functions of proteins
The functions of proteins in the body are diverse. They are largely due to the complexity and diversity of the forms and composition of the proteins themselves.
Construction (plastic) - proteins are involved in the formation of the cell membrane, organelles and cell membranes. Blood vessels, tendons, and hair are built from proteins.
Catalytic - all cellular catalysts are proteins (enzyme active sites).
Motor - contractile proteins cause all movement.
Transport - blood protein hemoglobin attaches oxygen and carries it to all tissues.
Protective - production of protein bodies and antibodies to neutralize foreign substances.
Energy - 1 g of protein is equivalent to 17.6 kJ.
Receptor - response to an external stimulus.
Formation of knowledge:
Students answer the questions:
What are proteins?
How many spatial structures of a protein molecule do you know?
What are the functions of proteins?
Set and announce grades.
Homework : § 38 without chemical properties. Prepare a message on the topic “Is it possible to completely replace protein foods with carbohydrates?”, “The role of proteins in human life”
lesson type - combined
Methods: partially exploratory, problematic presentation, explanatory and illustrative.
Target:
Formation in students of a holistic system of knowledge about wildlife, its systemic organization and evolution;
Ability to give a reasoned assessment of new information on biological issues;
Education of civic responsibility, independence, initiative
Tasks:
Educational: about biological systems (cell, organism, species, ecosystem); the history of the development of modern ideas about wildlife; outstanding discoveries in biological science; the role of biological science in shaping the modern natural-science picture of the world; methods of scientific knowledge;
Development creative abilities in the process of studying the outstanding achievements of biology, included in the universal culture; complex and contradictory ways of developing modern scientific views, ideas, theories, concepts, various hypotheses (about the essence and origin of life, man) in the course of working with various sources of information;
Upbringing conviction in the possibility of knowing wildlife, the need for careful attitude to the natural environment, one's own health; respect for the opinion of the opponent when discussing biological problems
Personal Outcomes of Learning Biology:
1. education of Russian civil identity: patriotism, love and respect for the Fatherland, a sense of pride in their homeland; awareness of one's ethnicity; assimilation of humanistic and traditional values of the multinational Russian society; fostering a sense of responsibility and duty to the Motherland;
2. formation of a responsible attitude to learning, readiness and ability of students for self-development and self-education based on motivation for learning and cognition, conscious choice and building a further individual trajectory of education based on orientation in the world of professions and professional preferences, taking into account sustainable cognitive interests;
Meta-subject learning outcomes in biology:
1. the ability to independently determine the goals of one's learning, set and formulate new tasks for oneself in study and cognitive activity, develop the motives and interests of one's cognitive activity;
2. mastering the components of research and project activities, including the ability to see the problem, raise questions, put forward hypotheses;
3. the ability to work with different sources of biological information: find biological information in various sources (textbook text, popular scientific literature, biological dictionaries and reference books), analyze and
evaluate information;
cognitive: selection of essential features of biological objects and processes; bringing evidence (argumentation) of human kinship with mammals; the relationship between man and the environment; dependence of human health on the state of the environment; the need to protect the environment; mastering the methods of biological science: observation and description of biological objects and processes; setting up biological experiments and explaining their results.
Regulatory: the ability to independently plan ways to achieve goals, including alternative ones, to consciously choose the most effective ways to solve educational and cognitive problems; the ability to organize educational cooperation and joint activities with the teacher and peers; work individually and in a group: find a common solution and resolve conflicts based on the coordination of positions and taking into account interests; formation and development of competence in the field of the use of information and communication technologies (hereinafter referred to as ICT competencies).
Communicative: the formation of communicative competence in communication and cooperation with peers, understanding the characteristics of gender socialization in adolescence, socially useful, educational, research, creative and other activities.
Technology : Health saving, problematic, developmental education, group activities
Receptions: analysis, synthesis, conclusion, transfer of information from one type to another, generalization.
During the classes
Tasks
To reveal the leading role of proteins in the structure and life of the cell. ,
Explain the structure of protein macromolecules that have the character of informational biopolymers.
To deepen the knowledge of schoolchildren about the relationship between the structure of the molecules of substances and their functions using the example of proteins.
Key points
The primary structure of a protein is determined by the genotype.
The secondary, tertiary and quaternary structural organization of a protein depends on the primary structure.
All biological catalysts - enzymes - are of a protein nature.
4.Protein molecules provide immunological protection of the body from foreign substances .
Issues for discussion
What: determines the specificity of the activity of biological catalysts - cops?
What is the mechanism of action of the fine surface receptor?
Biological polymers - proteins
Among the organic substances of the cell, proteins occupy the first place both in quantity and in value. In animals, they account for about 50% of the dry mass of the cell. In the human body, there are 5 million types of protein mo-, which differ not only from each other, but also from the proteins of other organisms. Despite such a variety and complexity of the structure, they are built from just 20 different amino acids.
Amino acids have a common structural plan, but differ from each other in the structure of the radical (K), which is very diverse. For example, the amino acid alanine has a simple radical - CH3, the cysteine radical contains sulfur - CH28H, other amino acids have more complex radicals.
Proteins isolated from living organisms of animals, plants and microorganisms include several hundred and sometimes thousands of combinations of 20 basic amino acids. The order of their alternation is the most diverse, which makes possible the existence of a huge number of protein molecules that differ from each other. For example, for a protein consisting of only 20 amino acid residues, about 2 are theoretically possible. 1018 variants of various protein molecules, differing in the alternation of amino acids, and hence in their properties. The sequence of amino acids in a polypeptide chain is commonly referred to as the primary structure of a protein.
However, a protein molecule in the form of a chain of amino acid residues connected in series by peptide bonds is not yet capable of performing specific functions. This requires a higher structural organization. By forming hydrogen bonds between the residues of carboxyl and amino groups of different amino acids, the protein molecule takes the form of a helix (a-structure) or a folded layer - "accordion" (P-structure). This is a secondary structure, but it is often not enough to acquire characteristic biological activity.
The secondary structure of the protein ((3-structure) is on top. The tertiary structure of the protein is on the bottom:
— ionic interactions,
- hydrogen bonds.
- disulfide bonds,
- hydrophobic interactions,
- hydrated groups
Often only a molecule with a tertiary structure can act as a catalyst or otherwise. Tertiary structure is formed due to the interaction of radicals, in particular radicals of the amino acid cysteine, which contain sulfur. The sulfur atoms of two amino acids located at some distance from each other in the polypeptide chain are connected, forming the so-called disulfide, or 8-8, bonds. Thanks to these interactions, as well as other, less strong bonds, the protein helix folds and takes on the shape of a ball, or globules. The way in which polypeptide helices fold into a globule is called the tertiary structure of a protein. Many proteins with a tertiary structure can fulfill their biological role in the cell. However, for the implementation of some body functions, the participation of proteins with an even higher level of organization is required. Such an organization is called Quaternary structure-swarm. It is a functional combination of several (two, three or more) protein molecules with a tertiary structural organization. An example of such a complex protein is hemoglobin. Its molecule consists of four interconnected molecules. Another example is the pancreatic hormone - insulin, which includes two components. The composition of the quaternary structure of some proteins includes, in addition to protein subunits, various non-protein components. The same hemoglobin contains a complex heterocyclic compound, which includes iron. Protein properties. Proteins, like other inorganic and organic compounds, have a number of physicochemical properties due to their structural organization. This largely determines the functional activity of each molecule. First, proteins are predominantly water-soluble molecules.
Secondly, protein molecules carry a large surface charge. This determines a number of electrochemical effects, such as changes in membrane permeability, catalytic activity of enzymes, and other functions.
Thirdly, proteins are thermolabile, i.e., they show their activity in a narrow temperature range.
The action of elevated temperature, as well as dehydration, changes in pH and other influences cause the destruction of the structural organization of proteins. First, the weakest structure is destroyed - Quaternary, then tertiary, secondary, and under more stringent conditions - primary. The loss of a protein molecule of its structural organization is called denaturation.
If a change in environmental conditions does not lead to the destruction of the primary structure of the molecule, then when normal environmental conditions are restored, the structure of the protein and its functional activity are completely recreated. This process is called renaturation. This property of proteins to completely restore the lost structure is widely used in the medical and food industries for the preparation of certain medical preparations, such as antibiotics, vaccines, sera, enzymes; to obtain food concentrates that retain their nutritional properties for a long time in dried form.
Protein functions. The functions of proteins in a cell are extremely diverse. One of the most important is the plastic (building) function: proteins are involved in the formation of all cell membranes and cell organelles, as well as extracellular structures.
The catalytic role of proteins is of exceptional importance. All biological catalysts - enzymes - are substances of a protein nature, they accelerate the chemical reactions that take place in the cell by tens and hundreds of thousands of times.
The interaction of an enzyme (F) with a substance (S), resulting in the formation of reaction products (P)
Let's take a closer look at this important function. The term "catalysis", which is no less common in biochemistry than in the chemical industry, where catalysts are widely used, literally means "unleashing", "liberation". The essence of a catalytic reaction, despite the huge variety of catalysts and types of reactions in which they take part, basically boils down to the fact that the starting materials form intermediate compounds with the catalyst. They relatively quickly turn into the final products of the reaction, and the catalyst is restored in its original form. Enzymes are the same catalysts. All the laws of catalysis apply to them. But enzymes are of a protein nature, and this gives them special properties. What do enzymes have in common with catalysts known from inorganic chemistry, for example, platinum, vanadium oxide and other inorganic reaction accelerators, and what distinguishes them? The same inorganic catalyst can be used in many different industries. Enzymes are active only at physiological values of the acidity of the solution, i.e. at such a concentration of hydrogen ions that is compatible with the life and normal functioning of a cell, organ or system.
Regulatory function of proteins consists in the implementation of their control of metabolic processes: insulin, pituitary hormones, etc.
motor function living organisms is provided with special contractile proteins. These proteins are involved in all types of movement that cells and organisms are capable of: the flickering of cilia and the movement of flagella in protozoa, muscle contraction in multicellular animals, the movement of leaves in plants, etc.
Transport function of proteins consists in the addition of chemical elements (for example, oxygen to hemoglobin) or biologically active substances (hormones) and their transfer to various tissues and organs of the body. Special transport proteins move RNA synthesized in the cell nucleus into the cytoplasm. Transport proteins are widely represented in the outer membranes of cells; they carry various substances from the environment into the cytoplasm.
When foreign proteins or microorganisms enter the body, special proteins are formed in white blood cells - leukocytes - antibodies. They are connected
They interact with substances (antigens) unusual for the body according to the principle of correspondence of spatial configurations of molecules (the “key-lock” principle). As a result, a harmless, non-toxic complex is formed - "antigen-antibody", which is subsequently phagocytosed and digested by other forms of leukocytes - this is a protective function.
Proteins can also serve as one of the sources of energy in the cell, that is, they perform an energy function. With complete breakdown of 1 g of protein to final products, 17.6 kJ of energy is released. However, proteins in this capacity are rarely used. Amino acids released during the breakdown of protein molecules are involved in plastic exchange reactions to build new proteins.
Questions and tasks for repetition
What organic substances are included in the composition of the cell?
What simple organic compounds are proteins made of?
What are peptides?
What is the primary structure of a protein?
How is the secondary, tertiary structure of a protein formed?
What is protein denaturation?
What functions of proteins do you know?
Choose the correct answer in your opinion.
1. Who discovered the existence of cells?
Robert Hooke
Carl Linnaeus
2. What is the cell filled with?
Cytoplasm
shell
3. What is the name of the dense body located in the cytoplasm?
nucleus
shell
organelles
4. Which of the organelles helps the cell to breathe?
lysosome
mitochondrion
membrane
5. What organelle gives green color to plants?
lysosome
chloroplast
mitochondrion
6. What substance is the most in inorganic cells?
water
mineral salts
7. What substances make up 20% of an organic cell?
Nucleic acids
Squirrels
8. What is the common name for the following substances: sugar, fiber, starch?
carbohydrates
9. Which of the substances gives 30% of the energy to the cell?
fats
carbohydrates
10. What substance is the most in the cell?
Oxygen
Amino acids, proteins. The structure of proteins. Levels of organization of a protein molecule
Video lessononbiology " Squirrels"
Functionsproteins
Resources
V. B. ZAKHAROV, S. G. MAMONTOV, N. I. SONIN, E. T. ZAKHAROVA TEXTBOOK "BIOLOGY" FOR GENERAL EDUCATIONAL INSTITUTIONS (grades 10-11).
AP Plekhov Biology with fundamentals of ecology. Series “Textbooks for universities. Special Literature.
A book for teachers Sivoglazov V.I., Sukhova T.S. Kozlova T. A. Biology: general patterns.
Presentation Hosting
"Life is a way of existence of protein bodies"
F. Engels.
None of the living organisms known to us can do without proteins. Proteins serve as nutrients, they regulate metabolism, acting as enzymes - catalysts for metabolism, promote the transfer of oxygen throughout the body and its absorption, play an important role in the functioning of the nervous system, are the mechanical basis of muscle contraction, participate in the transfer of genetic information, etc. d.
Proteins (polypeptides) - biopolymers built from α-amino acid residues connected peptide(amide) bonds. These biopolymers contain 20 types of monomers. These monomers are amino acids. Each protein in its chemical structure is a polypeptide. Some proteins are made up of several polypeptide chains. Most proteins contain an average of 300-500 amino acid residues. Several very short natural proteins, 3-8 amino acids long, and very long biopolymers, more than 1500 amino acids long, are known. The formation of a protein macromolecule can be represented as a polycondensation reaction of α-amino acids:
Amino acids are connected to each other due to the formation of a new bond between carbon and nitrogen atoms - peptide (amide):
From two amino acids (AA) you can get a dipeptide, from three - a tripeptide, from a larger number of AAs you can get polypeptides (proteins).
Functions of proteins
The functions of proteins in nature are universal. Proteins are part of the brain, internal organs, bones, skin, hairline, etc. main sourceα - amino acids for a living organism are food proteins, which, as a result of enzymatic hydrolysis in the gastrointestinal tract, giveα - amino acids. Manyα - amino acids are synthesized in the body, and some are necessary for the synthesis of proteins α Amino acids are not synthesized in the body and must be supplied from outside. Such amino acids are called essential. These include valine, leucine, threonine, methionine, tryptophan, and others (see table). In some human diseases, the list of essential amino acids is expanding.
· catalytic function - carried out with the help of specific proteins - catalysts (enzymes). With their participation, the speed of various metabolic and energy reactions in the body increases.
Enzymes catalyze the reactions of splitting complex molecules (catabolism) and their synthesis (anabolism), as well as DNA replication and RNA template synthesis. Several thousand enzymes are known. Among them, such as, for example, pepsin, break down proteins during digestion.
· transport function - binding and delivery (transport) of various substances from one organ to another.
So, the protein of red blood cells, hemoglobin, combines with oxygen in the lungs, turning into oxyhemoglobin. Reaching the organs and tissues with the blood flow, oxyhemoglobin is broken down and gives off the oxygen necessary to ensure oxidative processes in the tissues.
· Protective function - binding and neutralization of substances entering the body or resulting from the vital activity of bacteria and viruses.
The protective function is performed by specific proteins (antibodies - immunoglobulins) formed in the body (physical, chemical and immune defense). For example, fibrinogen, a blood plasma protein, performs a protective function by participating in blood coagulation and thereby reducing blood loss.
· Contractile function (actin, myosin) - as a result of the interaction of proteins, there is movement in space, contraction and relaxation of the heart, and movement of other internal organs.
· structural function Proteins form the basis of the cell structure. Some of them (connective tissue collagen, hair, nail and skin keratin, vascular wall elastin, wool keratin, silk fibroin, etc.) perform an almost exclusively structural function.
In combination with lipids, proteins are involved in the construction of cell membranes and intracellular formations.
· Hormonal (regulatory) function - the ability to transmit signals between tissues, cells or organisms.
Carry out proteins-regulators of metabolism. They refer to hormones that are formed in the endocrine glands, some organs and tissues of the body.
· nutritional function - carried out by reserve proteins, which are stored as a source of energy and matter.
For example: casein, egg albumin, egg proteins ensure the growth and development of the fetus, and milk proteins serve as a source of nutrition for the newborn.
The various functions of proteins are determined by the α-amino acid composition and structure of their highly organized macromolecules.
Physical properties of proteins
Proteins are very long molecules that consist of amino acid units linked by peptide bonds. These are natural polymers, the molecular weight of proteins ranges from several thousand to several tens of millions. For example, milk albumin has a molecular weight of 17400, blood fibrinogen - 400,000, virus proteins - 50,000,000. Each peptide and protein has a strictly defined composition and sequence of amino acid residues in the chain, which determines their unique biological specificity. The number of proteins characterizes the degree of complexity of the organism (E. coli - 3000, and in the human body there are more than 5 million proteins).
The first protein we get to know in our lives is the protein of a chicken egg, albumin - we dissolve well in water, it coagulates when heated (when we fry eggs), and when stored for a long time in heat, it breaks down, the egg rots. But the protein is hidden not only under the eggshell. Hair, nails, claws, wool, feathers, hooves, the outer layer of skin - they are all almost entirely composed of another protein, keratin. Keratin does not dissolve in water, does not coagulate, does not break down in the earth: the horns of ancient animals are preserved in it as well as bones. And the protein pepsin contained in the gastric juice is able to destroy other proteins, this is the process of digestion. Protein inreferon is used in the treatment of rhinitis and flu, because. kills the viruses that cause these diseases. And the protein of snake venom is capable of killing a person.
Protein classification
From the point of view of the nutritional value of proteins, determined by their amino acid composition and the content of the so-called essential amino acids, proteins are divided into full-fledged and defective . Complete proteins are mainly proteins of animal origin, with the exception of gelatin, which is classified as incomplete proteins. Incomplete proteins are predominantly of vegetable origin. However, some plants (potatoes, legumes, etc.) contain complete proteins. Of animal proteins, the proteins of meat, eggs, milk, etc. are especially valuable for the body.
In addition to peptide chains, many proteins also contain non-amino acid fragments; according to this criterion, proteins are divided into two large groups - simple and complex proteins (proteins). Simple proteins contain only amino acid chains, complex proteins also contain non-amino acid fragments ( For example, hemoglobin contains iron).
According to the general type of structure, proteins can be divided into three groups:
1. fibrillar proteins - are insoluble in water, form polymers, their structure is usually highly regular and is maintained mainly by interactions between different chains. Proteins having an elongated filamentous structure. The polypeptide chains of many fibrillar proteins are parallel to each other along one axis and form long fibers (fibrils) or layers.
Most fibrillar proteins are insoluble in water. Fibrillar proteins include, for example, α-keratins (they account for almost the entire dry weight of hair, proteins of wool, horns, hooves, nails, scales, feathers), collagen - tendon and cartilage protein, fibroin - silk protein).
2. Globular proteins - water-soluble, the general shape of the molecule is more or less spherical. Among globular and fibrillar proteins, subgroups are distinguished. Globular proteins include enzymes, immunoglobulins, some hormones of a protein nature (for example, insulin), as well as other proteins that perform transport, regulatory and auxiliary functions.
3. Membrane proteins - have domains that cross the cell membrane, but parts of them protrude from the membrane into the intercellular environment and the cytoplasm of the cell. Membrane proteins perform the function of receptors, that is, they carry out signal transmission, and also provide transmembrane transport of various substances. Transporter proteins are specific, each of them allows only certain molecules or a certain type of signal to pass through the membrane.
Proteins are an integral part of the food of animals and humans. A living organism differs from a non-living organism primarily in the presence of proteins. Living organisms are characterized by a huge variety of protein molecules and their high orderliness, which determines the high organization of a living organism, as well as the ability to move, contract, reproduce, the ability to metabolism and to many physiological processes.
The structure of proteins
Fischer Emil German, German organic chemist and biochemist. In 1899 he began work on the chemistry of proteins. Using the ethereal method for analyzing amino acids, which he created in 1901, F. was the first to carry out qualitative and quantitative determinations of protein cleavage products, discovered valine, proline (1901) and hydroxyproline (1902), and experimentally proved that amino acid residues are linked together by a peptide bond; in 1907 he synthesized an 18-membered polypeptide. F. showed the similarity of synthetic polypeptides and peptides obtained as a result of protein hydrolysis. F. also studied tannins. F. created a school of organic chemists. Foreign Corresponding Member of the St. Petersburg Academy of Sciences (1899). Nobel Prize (1902).
Squirrels- macromolecular compounds, heteropolymers, the monomers of which are amino acids. The human body contains more than 5 million types of protein molecules. The diversity of proteins is provided by combinations of 20 amino acids - the basic amino acids. All amino acids are divided into essential and non-essential.
Replaceable are synthesized in the body, irreplaceable - enter the body with food.
Proteins are made up of amino acids that are linked together by peptide bonds. Amino acids contain carboxyl groups (-COOH) with acidic properties and amino groups (-NH2) with alkaline properties, so they are amphoteric compounds. A peptide bond is formed between the carboxyl group of one amino acid and the amino group of another.
When two amino acids interact, a dipeptide is formed. When a peptide bond is formed, a water molecule is detached.
There are 4 levels of organization of a protein molecule: primary, secondary, tertiary, quaternary.
The primary structure of proteins is the simplest. It has the form of a polypeptide chain, where amino acids are linked by a peptide bond. It is determined by the qualitative and quantitative composition of amino acids and their sequence. This sequence is determined by the hereditary program, so the proteins of each organism are strictly specific.
Hydrogen bonds between peptide groups are the basis of the secondary structure of proteins. The main types of secondary structures.
The secondary structure of the protein arises as a result of the formation of hydrogen bonds between the hydrogen atoms of the NH group of one helix of the helix and the oxygen of the CO group of the other helix and are directed along the helix or between parallel folds of the protein molecule. Despite the fact that hydrogen bonds are weak, their significant amount in the complex provides a fairly strong structure.
The protein molecule is partially twisted into an a-helix (write Greek alpha) or forms a B-fold (write Greek beta) structure.
Keratin proteins form an a-helix (alpha). They are part of the hooves, horns, hair, feathers, nails, claws.
The proteins that make up silk have a folded (beta) structure. From the outside of the helix, amino acid radicals remain (in Fig. R1. R2, R3 ...)
