Protective function of proteins. Structure and functions of proteins

Proteins are building material body and participate in the metabolic process. The functions of proteins in the body are of great importance for maintaining life.

Structure

Proteins are biopolymers consisting of individual units - monomers, which are called amino acids. They consist of a carboxyl (-COOH), an amine (-NH2) group and a radical. Amino acids are linked to each other using a peptide bond (-C(O)NH-), forming a long chain.

Mandatory chemical elements amino acids:

carbon;
hydrogen;
nitrogen;
oxygen.

Rice. 1. Protein structure.

The radical may include sulfur and other elements. Proteins differ not only in the radical, but also in the number of carboxyl and amine groups. Due to this There are three types of amino acids:

neutral (-COOH and -NH2);
basic (-COOH and several -NH2);
acidic (several -COOH and -NH2).

In accordance with the ability to be synthesized inside the body, they are isolated two types of amino acids:

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replaceable - synthesized in the body;
irreplaceable - are not synthesized in the body and must come from the external environment.

About 200 amino acids are known. However, only 20 are involved in the construction of proteins.

Synthesis

Protein biosynthesis occurs on the ribosomes of the endoplasmic reticulum. It's a complex process consisting of two stages:

formation of a polypeptide chain;
protein modification.

Synthesis of the polypeptide network occurs with the help of matrix and transfer RNA. This process is called translation. The second stage includes “working on mistakes.” Parts of the synthesized protein are replaced, removed, or extended.

Rice. 2. Protein synthesis.

Functions

The biological functions of proteins are presented in the table.

*Function*	*Description*	*Examples*
Transport	Transport chemical elements to cells and back to the external environment	Hemoglobin carries oxygen and carbon dioxide, transcortin - adrenal hormone into the blood
Motor	Helps muscles contract in multicellular animals	Actin, myosin
Structural	Provide strength to tissues and cellular structures	Collagen, fibroin, lipoproteins
Construction	Participate in the formation of tissues, membranes, cell walls. Composed of muscles, hair, tendons	Elastin, keratin
Signal	Transmit information between cells, tissues, organs	Cytokines
Enzymatic or catalytic	Most enzymes in the body of animals and humans are of protein origin. They are a catalyst for many bio chemical reactions(speed up or slow down)	Enzymes
Regulatory or hormonal	Hormones protein origin control and regulate metabolic processes	Insulin, lutropin, thyrotropin
Gene regulatory	Regulate the functions of nucleic acids during the transfer of genetic information	Histones regulate DNA replication and transcription
Energy	Used as an additional source of energy. When 1 g disintegrates, 17.6 kJ is released	Break down after exhaustion of other energy sources - carbohydrates and fats
Protective	Specific proteins - antibodies - protect the body from infection by destroying foreign particles. Special proteins clot blood, stopping bleeding	Immunoglobulins, fibrinogen, thrombin
Storage	They are stored to feed cells. Retains substances needed by the body	Ferritin retains iron, casein, gluten, albumin are stored in the body
Receptor	Keep various regulators (hormones, mediators) on the surface or inside the cell	Glucagon receptor, protein kinase

Proteins can have a poisonous and neutralizing effect. For example, the botulism bacillus secretes a toxin of protein origin, and the protein albumin binds heavy metals.

Enzymes

It is worth saying briefly about the catalytic function of proteins. Enzymes or enzymes are classified into a special group of proteins. They carry out catalysis - acceleration of a chemical reaction.
According to their structure, enzymes can be:

simple - contain only amino acid residues;
complex - in addition to the protein monomer residue, they include non-protein structures called cofactors (vitamins, cations, anions).

Enzyme molecules have an active part (active center) that binds the protein to a substance - the substrate. Each enzyme “recognizes” a specific substrate and binds to it. The active site is usually a "pocket" into which the substrate enters.

The binding of the active site and substrate is described by the induced fit model (hand-glove model). The model shows that the enzyme “adapts” to the substrate. By changing the structure, the energy and resistance of the substrate are reduced, which helps the enzyme more easily transfer it to the product.

Rice. 3. Hand-glove model.

Enzyme activity depends on several factors:

temperature;
enzyme and substrate concentrations;
acidity.

There are 6 classes of enzymes, each of which interacts with certain substances. For example, transferases transfer a phosphate group from one substance to another.

Enzymes can speed up reactions 1000 times.

What have we learned?

We found out what functions proteins perform in a cell, how they are structured and how they are synthesized. Proteins are polymer chains made up of amino acids. There are 200 known amino acids, but proteins can form only 20. Protein polymers are synthesized on ribosomes. Proteins perform important functions in the body: transport substances, accelerate biochemical reactions, control processes occurring in the body. Enzymes bind the substrate and purposefully transfer it to substances, speeding up reactions by 100-1000 times.

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Just like other biological macromolecules (polysaccharides, lipids and nucleic acids), proteins are necessary components of all living organisms and play a decisive role in the life of the cell. Proteins carry out metabolic processes. They are part of intracellular structures - organelles and cytoskeleton, secreted into the extracellular space, where they can act as a signal transmitted between cells, participate in the hydrolysis of food and the formation of intercellular substance.

The classification of proteins according to their functions is quite arbitrary, since the same protein can perform several functions. A well-studied example of such multifunctionality is lysyl-tRNA synthetase, an enzyme from the class of aminoacyl-tRNA synthetases, which not only attaches a lysine residue to tRNA, but also regulates the transcription of several genes. Proteins perform many functions due to their enzymatic activity. Thus, the enzymes are the motor protein myosin, regulatory proteins protein kinases, transport protein sodium-potassium adenosine triphosphatase, etc.

Molecular model of bacterial urease enzyme Helicobacter pylori

Catalytic function

Most good known function proteins in the body - catalysis of various chemical reactions. Enzymes are proteins that have specific catalytic properties, that is, each enzyme catalyzes one or more similar reactions. Enzymes catalyze reactions that break down complex molecules (catabolism) and synthesize them (anabolism), including DNA replication and repair and template RNA synthesis. By 2013, more than 5,000 thousand enzymes had been described. Acceleration of reaction as a result enzymatic catalysis can be enormous: for example, a reaction catalyzed by the enzyme orotidine 5"-phosphate decarboxylase proceeds 10 17 times faster than an uncatalyzed one (the half-life of orotic acid decarboxylation is 78 million years without the enzyme and 18 milliseconds with the participation of the enzyme). Molecules that attach to enzyme and change as a result of the reaction are called substrates.

Despite the fact that enzymes usually consist of hundreds of amino acid residues, only a small part of them interact with the substrate, and an even smaller number - on average 3-4 amino acid residues, often located far apart in primary structure- directly participate in catalysis. The part of the enzyme molecule that mediates substrate binding and catalysis is called the active site.

International Union of Biochemistry and molecular biology in 1992 proposed the final version of the hierarchical nomenclature of enzymes based on the type of reactions they catalyze. According to this nomenclature, the names of enzymes must always have the ending - aza and are formed from the names of the catalyzed reactions and their substrates. Each enzyme is assigned an individual code, which makes it easy to determine its position in the enzyme hierarchy. Based on the type of reactions they catalyze, all enzymes are divided into 6 classes:

CF 1: Oxidoreductases that catalyze redox reactions;
CF 2: Transferases catalyzing transfer chemical groups from one substrate molecule to another;
EF 3: Hydrolases catalyzing hydrolysis chemical bonds;
EF 4: Lyases that catalyze the breaking of chemical bonds without hydrolysis with the formation of a double bond in one of the products;
EC 5: Isomerases that catalyze structural or geometric changes in the substrate molecule;
EC 6: Ligases that catalyze the formation of chemical bonds between substrates due to the hydrolysis of the diphosphate bond of ATP or a similar triphosphate.

Structural function

More details: Structural function of proteins, Fibrillar proteins

Structural proteins of the cytoskeleton, like a kind of reinforcement, give shape to cells and many organelles and are involved in changing the shape of cells. Most of structural proteins are filamentous: for example, the monomers of actin and tubulin are globular, soluble proteins, but after polymerization they form long filaments that make up the cytoskeleton, allowing the cell to maintain its shape. Collagen and elastin are the main components of the intercellular substance of connective tissue (for example, cartilage), and another structural protein, keratin, consists of hair, nails, bird feathers and some shells.

Protective function

More details: Protective function proteins

There are several types of protective functions of proteins:

Physical protection. Physical protection of the body is provided by Collagen - a protein that forms the basis of the intercellular substance of connective tissues (including bones, cartilage, tendons and deep layers of skin (dermis)); keratin, which forms the basis of horny scutes, hair, feathers, horns and other derivatives of the epidermis. Typically, such proteins are considered to be proteins with a structural function. Examples of proteins in this group are fibrinogens and thrombins, which are involved in blood clotting.
Chemical protection. The binding of toxins by protein molecules can ensure their detoxification. Liver enzymes play a particularly decisive role in detoxification in humans, breaking down poisons or converting them into a soluble form, which facilitates their rapid elimination from the body.
Immune protection. Proteins that make up blood and other biological fluids are involved in the body's protective response to both damage and attack by pathogens. Proteins of the complement system and antibodies (immunoglobulins) belong to the proteins of the second group; they neutralize bacteria, viruses or foreign proteins. Antibodies that are part of the adaptive immune system attach to substances, antigens, that are foreign to a given organism, and thereby neutralize them, directing them to places of destruction. Antibodies can be secreted into the extracellular space or embedded in the membranes of specialized B lymphocytes called plasma cells.

Regulatory function

More details: Activator (proteins), Proteasome, Regulatory function of proteins

Many processes inside cells are regulated by protein molecules, which serve neither as a source of energy nor as building material for the cell. These proteins regulate cell progression through the cell cycle, transcription, translation, splicing, the activity of other proteins, and many other processes. Proteins perform their regulatory function either through enzymatic activity(for example, protein kinases), or due to specific binding to other molecules. Thus, transcription factors, activator proteins and repressor proteins, can regulate the intensity of gene transcription by binding to their regulatory sequences. At the translation level, the reading of many mRNAs is also regulated by the addition of protein factors.

The most important role in the regulation of intracellular processes is played by protein kinases and protein phosphatases - enzymes that activate or suppress the activity of other proteins by attaching or removing phosphate groups to them.

Signal function

More details: Protein signaling function, Hormones, Cytokines

The signaling function of proteins is 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 transmit signals.

The signaling function is performed by proteins - Hormones, Cytokines, growth factors, etc.

Hormones are carried in the blood. Most animal hormones are proteins or peptides. The binding of a hormone to its receptor is a signal that triggers a cell response. Hormones regulate the concentrations 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.

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

Cytokines are peptide signaling molecules. They regulate interactions between cells, determine their survival, stimulate or suppress growth, differentiation, functional activity and apoptosis, ensure coordination of the actions of the immune, endocrine and nervous systems. An example of cytokines is tumor necrosis factor, which transmits inflammatory signals between body cells.

Transport function

More details: Transport function proteins

Soluble proteins involved in the transport of small molecules must have a high affinity for the substrate when it is present in high concentration, and is easy to release in areas of low substrate concentration. An example of transport proteins is hemoglobin, which transports oxygen from the lungs to other tissues and carbon dioxide from tissues to the lungs, and in addition to proteins homologous to it, found in all kingdoms of living organisms.

Some membrane proteins are involved in the transport of small molecules across the cell membrane, changing its permeability. The lipid component of the membrane is waterproof (hydrophobic), which prevents the diffusion of polar or charged (ions) molecules. Membrane transport proteins are usually divided into channel proteins and carrier proteins. Channel proteins contain internal water-filled pores that allow ions (via ion channels) or water molecules (via aquaporin proteins) to move across the membrane. Many ion channels are specialized to transport only one ion; Thus, potassium and sodium channels often distinguish between these similar ions and allow only one of them to pass through. Transporter proteins bind, like enzymes, each transported molecule or ion and, unlike channels, can carry out active transport using the energy of ATP. “The powerhouse of the cell” - ATP synthase, which synthesizes ATP due to the proton gradient, can also be classified as a membrane transport protein.

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, 7S and 11S globulins) and animal eggs. A number of other proteins are used in the body as a source of amino acids, which in turn are biologically precursors active substances regulating metabolic processes.

Receptor function

More details: Cell receptor

Protein receptors can be located both in the cytoplasm and embedded in the cell membrane. One part of the receptor molecule senses a signal, often a chemical, and in some cases light, mechanical stress (such as stretching), or other stimuli. When a signal acts on a certain part of the molecule - the receptor protein - its conformational changes occur. As a result, the conformation of another part of the molecule, which transmits the signal to other cellular components, changes. There are several signal transmission mechanisms. Some receptors catalyze a specific chemical reaction; others serve as ion channels that open or close when triggered by a signal; still others specifically bind intracellular messenger molecules. In membrane receptors, the part of the molecule that binds to the signaling molecule is located on the surface of the cell, and the domain that transmits the signal is inside.

Motor (motor) function

A whole class of motor proteins provides body movements, for example, muscle contraction, including locomotion (myosin), movement of cells within the body (for example, amoeboid movement of leukocytes), movement of cilia and flagella, and in addition active and directed intracellular transport (kinesin, dynein ). Dyneins and kinesins transport molecules along microtubules using ATP hydrolysis as an energy source. Dyneins transport molecules and organelles from the peripheral parts of the cell towards the centrosome, kinesins - in the opposite direction. Dyneins are also responsible for the movement of cilia and flagella in eukaryotes. Cytoplasmic variants of myosin can be involved in the transport of molecules and organelles along microfilaments.

A similar function of physical protection is performed structural proteins, which make up the cell walls of some protists (for example, the green alga Chlamydomonas) and viral capsids.

The physical protective functions of proteins include the ability of blood to clot, which is provided by the protein fibrinogen contained in the blood plasma. Fibrinogen is colorless; when the blood begins to clot, it is cleaved by the enzyme [[tro after cleavage, a monomer is formed - fibrin, which, in turn, polymerizes and precipitates into white threads). Fibrin, precipitating, makes the blood not liquid, but gelatinous. In the process of blood clotting, the fundamental protein - after it has formed a precipitate, from fibrin strands and red blood cells, when fibrin is compressed, forms a strong red thrombus.

Chemical protective function

The protective proteins of the immune system also include interferons. These proteins are produced by cells infected with viruses. Their effect on a cell neighbor provides antiviral resistance by blocking the multiplication of viruses or the assembly of viral particles in target cells. Interferons also have other mechanisms of action, for example, they affect the activity of lymphocytes and other cells of the immune system.

Active protective function

Protein poisons of animals

Squirrels can also serve to protect against predators or attack prey. Such proteins and peptides are found in the venoms of most animals (for example, snakes, scorpions, cnidarians, etc.). The proteins contained in poisons have different mechanisms of action. Thus, the venoms of viper snakes often contain the enzyme phospholipase, which causes destruction cell membranes and, as a result, hemolysis of red blood cells and hemorrhage. Adder venom is dominated by neurotoxins; for example, krait venom contains proteins α-bungarotoxin (a blocker of nicotinic acetylcholine receptors and β-bungarotoxin (causes a constant release of acetylcholine from nerve endings and thereby depleting its reserves); joint action These poisons cause death from muscle paralysis.

Bacterial protein poisons

Bacterial protein poisons - botulinum toxin, tetanospasmin toxin produced by the causative agents of tetanus, diphtheria toxin of the causative agent of diphtheria, cholera toxin. Many of them are a mixture of several proteins with different mechanisms of action. Some bacterial toxins of protein nature are very strong poisons; components of botulinum toxin are the most toxic of known natural substances.

Toxins pathogenic bacteria sort of Clostridium, apparently, are required by anaerobic bacteria to influence the entire body as a whole, to lead it to death - this allows the bacteria to feed and reproduce “with impunity”, and having already greatly increased their population, leave the body in the form of spores.

The biological significance of the toxins of many other bacteria is not precisely known.

Protein plant poisons

In plants, non-protein substances (alkaloids, glycosides, etc.) are usually used as poisons. However, plants also contain protein toxins. Thus, castor bean seeds (plants of the spurge family) contain the protein toxin ricin. This toxin penetrates the cytoplasm of intestinal cells, and its enzymatic subunit, acting on ribosomes, irreversibly blocks translation.

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To the main, and in some sense unique biological functions proteins that are unusual or only partially inherent in other classes of biopolymers include the following functions.

Structural (support) function

Collagen fibers perform a supporting function. (Electron microscopy)

Proteins that perform structural function, predominate among other proteins in the human body. Fibrillar proteins form the substance of connective tissue - collagen, elastin (in the vascular wall of elastic-type vessels), keratin (in the skin and its derivative elements), proteoglycans.

Enzymatic (catalytic) function

All enzymes are proteins that determine the rate of chemical reactions in biological systems. But at the same time, there is experimental data on the existence of ribozymes, that is ribonucleic acid, having catalytic activity, and abzymes - and mono- and polyclonal antibodies.

Receptor and hormonal function

Transport function

Only proteins carry out the transport of substances in the blood, for example, lipoproteins (fat transport), hemoglobin (oxygen transport), transferrin (iron transport). Proteins transport calcium, magnesium, iron, copper and other ions in the blood.

The transport of substances across membranes is carried out by proteins - Na + , K + -ATPase (anti-directional transmembrane transport of sodium and potassium ions), Ca 2+ -ATPase (pumping calcium ions out of the cell), glucose transporters.

Reserve (nutritional) function

This function is performed by so-called reserve proteins. An example of a stored protein is the production and accumulation of ovalbumin (ovalbumin) in the egg. Animals and humans do not have such specialized depots, but during prolonged fasting, proteins from muscles, lymphoid organs, epithelial tissues and the liver are used. The main protein in milk (casein) also has a primarily nutritional function.

Contractile function

There are a number of intracellular proteins designed to change the shape of the cell and the movement of the cell itself or its organelles. The main role in the processes of movement is played by actin and myosin - specific proteins of muscle tissue, and the cytoskeletal protein tubulin, which ensures the finest processes of cell life - the divergence of chromosomes during mitosis.

Protective function

Functions of blood proteins

In the regulation of plasma protein content at a certain level great importance has a liver that completely synthesizes fibrinogen and blood albumin, mostα- and β-globulins, cells of the reticuloendothelial system of the bone marrow and lymph nodes.

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BIBLIOGRAPHY

CONCLUSIONS

However, the main personal qualities of an entrepreneur are: independence; ambition; persistence; hard work; durability. The presence of such personality traits is one of the most important conditions success.

In addition to personal qualities, an entrepreneur must have a set of specific knowledge, skills and abilities in the area in which he works. It is clear that in order to successfully conduct financial transactions, an entrepreneur needs at least a minimum set of knowledge in the financial and credit field and accounting͵ and a person who decides to organize furniture production must have a minimum technical education. However, these restrictions are not decisive. It often happened that the entrepreneur received specialized knowledge and skills already during the development of his business, and in its first stages he acted either intuitively or with the help of attracted specialists. The main thing here is the desire to learn and improve your skills in order to improve your business, and such a desire already applies to personal qualities(curiosity, perseverance, ambition).

Researching the personality of an entrepreneur using psychological tests not only helps to clarify certain aspects of his personality, but also shows in which direction he should work on himself in order to increase the efficiency of his entrepreneurial activities.

Akperov I. G., Maslikova Zh. V. Psychology of entrepreneurship. - M: Finance and Statistics, 2003.

Zavyalova E. K., Posokhova S. T. Psychology of entrepreneurship: Tutorial. - SPb.: Publishing house. St. Petersburg State University, 2004.

Meneghetti A. Psychology of a leader. - M., 2001. - P. 15.

Platonov K.K. Structure and development of personality. - M.: Nauka, 1986. P. 24.

Entrepreneurship: Textbook / Ed. M. L. Lapusty. - M.: INFRA-M, 2003.

Stephen J. Train your dragons. - St. Petersburg: Peter-press, 1996.

Shcherbatykh Yu. V. Psychology of entrepreneurship and business: Textbook. - St. Petersburg: Peter, 2008. P. 45.

Shcherbatykh Yu. V. Psychology of success. - M.: Eksmo, 2005.

· Mucous membrane is quite smooth

Lubricated with mucus (produced by the mucous glands of the shell itself)

· Mucus – envelops the m/o, its viscosity prevents it from penetrating into the bloodstream

Accumulation of lymphoid tissue - consists of lymphocytes varying degrees maturity. Lymphoid tissue forms clusters:

ü Tonsils - located at the very beginning of the digestive and respiratory tubes:

o Palatine tonsils – on both sides of the pharynx

o Lingual – in the area of the root of the tongue

o Pharyngeal tonsil – located near the upper and posterior wall of the nasopharynx (vault) under the tuberculum faringeum

o Tubal tonsils – near the pharyngeal opening of the auditory tube

ü Single follicles – located throughout the entire length of the body, their total weight is about 2 kg;

ü Lymphoid plaques - contain dozens of lymphocytes, are found only in the ileum - Peyer's patches, their number is about 20-30

ü Vermiform appendix – its mucous membrane contains lymphoid tissue. This tonsil.

· Alternation different environments along the digestive tube.

When protective devices are weakened, immunity decreases!!!

- chemical food processing- carried out by digestive juices, which are produced by the digestive glands. Throughout the p.t. there are glands:

By size:

· Large

Large salivary glands (parotid, submandibular, sublingual)

Liver - produces bile that goes into the duodenum

Pancreas – pancreatic juice, insulin.

Minor salivary glands (labial, buccal, palatine, lingual)

Gastric glands

Intestinal glands - in the mucosa of the small intestine

By localization:

· In the thickness of the mucous membrane

Minor salivary

Gastric

Glands of the jejunum and ileum of the small intestine

Under the mucous layer

Glands of the duodenum

Outside the digestive tube

All large glands

Chemical treatment in the oral cavity - saliva, in the stomach - gastric juice, 12pk - bile, pancreatic juice. and glands 12pk itself, in the jejunum and ileum - under the influence of its own juices. The chemical treatment ends in the small intestine. In the colon, fiber is broken down under the influence of microorganisms (m/o).

- absorption of nutrients– nutrients are absorbed into the blood and lymphatic vessels. Suction begins:

· In the oral cavity (medicines, alcohol)

· Stomach (l/s, alcohol, nutritional substances)

· Small intestine – main process of absorption

Large intestine - mainly water is absorbed

The small intestine is long, its mucosa has:

1. Circular folds, they increase the suction surface. Valves form at the border between departments

2. Villi – from 1.5 to 4 million, height 1 mm, the wall is very thin.

3. Crypts - depressions in the mucosa

4. Epithelial cells have outgrowths - microvilli (up to 300 per cell).

Τᴀᴋᴎᴍ ᴏϬᴩᴀᴈᴏᴍ, the area of the mucous membrane is 1500 m 2.

Submucosal layer. Consists of loose connective tissue. Purpose:

Fixes the mucous membrane to the muscle membrane;

Provides movable fixation - the mucous membrane forms folds

Vessels and nerves pass through

Muscular membrane. Formed by smooth muscle tissue. But around the oral cavity, the muscles of the pharynx, the upper third of the esophagus, Bottom part rectum - striated.

The muscular lining of the digestive tube forms two layers:

Longitudinal - external)

· Shortens the digestive tube,

· Straightens kinks

Transverse (circular) – internal

Provides peristalsis - wave-like narrowing of the intestinal lumen

· Forms sphincters - local thickenings between the sections of the pt. (esophagus - stomach, stomach - 12pcs, small intestine - large intestine, in the lower part of the rectum).

The sphincters are strengthened by valves - opposite the sphincter, the mucous membrane forms a circular fold. In the mucous membrane under the valves there are venous plexuses.

Sphincter + Valve + Venous plexus = closure apparatus.

Purpose: prevention of premature emptying of the adjacent section; prevents content from flowing backwards.

Only the stomach has three layers (+ oblique layer), since it acts as a reservoir and mixes food. The three layers also have the uterus, bladder, heart - the reservoir must be completely emptied.

Outer shell.

The connective tissue membrane is not in the abdominal cavity: the pharynx, esophagus, rectum are outside. Consists of a loose connective tissue membrane:

· Attachs organs to bones

· Connects organs with each other. There are no voids between the organs; they are filled with loose connective tissue

Provides organ mobility – ensures functional organ mobility

· Vessels and nerves pass through it (in the adventitial layers)

The serous membrane is the organs of the abdominal cavity, formed by the peritoneum. Same purposes as the joint fabric shell.

Protective function - concept and types. Classification and features of the category "Protective function" 2017, 2018.