The actin protein is included. Structure and functions of microfilaments
BIOCHEMISTRY OF SPORTS
Structure and function of muscle fiber
There are 3 types of muscle tissue:
Striated skeletal;
Striated heart;
Smooth.
Functions of muscle tissue.
Striated skeletal tissue - makes up approximately 40% of the total body weight.
Its functions:
dynamic;
static;
receptor (for example, proprioceptors in tendons - intrafusal muscle fibers (fusiform));
depositing - water, minerals, oxygen, glycogen, phosphates;
thermoregulation;
emotional reactions.
Striated cardiac muscle tissue.
The main function is injection.
Smooth muscle - forms the wall of hollow organs and blood vessels.
Its functions: - maintains pressure in hollow organs; - maintains blood pressure;
Ensures the movement of contents through the gastrointestinal tract and ureters.
Chemical composition of muscle tissue
The chemical composition of muscle tissue is very complex and changes under the influence of various factors. Average chemical composition well-prepared muscle tissue is: water - 70-75% of the tissue mass; proteins - 18-22%; lipids - 0.5-3.5%; nitrogenous extractives - 1.0-1.7%; nitrogen-free extractives - 0.7-1.4%; minerals - 1.0-1.5%.
About 80% of the dry residue of muscle tissue consists of proteins, the properties of which largely determine the properties of this tissue.
MYOFIBRILS - contractile elements of muscle fiber. Fine structure of myofibrils
Myofibrils are thin fibers (their diameter is 1-2 microns, length 2-2.5 microns), containing 2 types of contractile proteins (protofibrils): thin filaments of actin and twice as thick filaments of myosin. They are arranged in such a way that there are 6 actin filaments around the myosin filaments, and 3 myosin filaments around each actin filament. Myofibrils are divided by Z-membranes into separate sections - sarcomeres, in the middle part of which there are predominantly myosin filaments, aactin filaments are attached to Z-membranes on the sides of the sarcomere. ( Different ability actin and myosin refract light, creating a striated appearance in a light microscope when the muscle is at rest).
Actin filaments make up about 20% of the dry weight of myofibrils. Actin consists of two forms of protein: 1) globular form - in the form of spherical molecules and 2) rod-shaped tronomyosin molecules, twisted in the form of double-stranded helices into a long chain. Along this double actin filament, each turn contains 14 molecules of globular actin (7 molecules on both sides), like a string of beads, as well as Ca2+ binding sites. These centers contain a special protein (troponin) that is involved in the formation of actin-myosin bonds.
Myosin is composed of parallel protein filaments (this part is the so-called light meromyosin). At both ends there are necks extending to the sides with thickenings - heads (this part is heavy meromyosin), thanks to which cross bridges are formed between myosin and actin.
Physicochemical properties and structural organization of contractile proteins (myosin and actin). Tropomyosin and troponin.
Myofibrillar proteins include the contractile proteins myosin, actin, and actomyosin, as well as the regulatory proteins tropomyosin, troponin, and alpha and beta actin. Myofibrillar proteins provide muscle contractile function.
Myosin is one of the main muscle contractile proteins, making up about 55% of the total muscle proteins. It consists of thick threads (filaments) of myofibrils. The molecular weight of this protein is about 470,000. The myosin molecule has a long fibrillar part and globular structures (heads). The fibrillar part of the myosin molecule has a double-helix structure. The molecule consists of six subunits: two heavy polypeptide chains (molecular weight 200,000) and four light chains (molecular weight 1500-2700), located in the globular part. The main function of the fibrillar part of the myosin molecule is the ability to form well-ordered bundles of myosin filaments or thick protofibrils. The active center of ATPase and the actin-binding center are located on the heads of the myosin molecule, so they ensure ATP hydrolysis and interaction with actin filaments.
Actin is the second contractile muscle protein that forms the basis of thin filaments. Two of its forms are known: globular G-actin and fibrillar F-actin. Globular actin is a spherical protein with a molecular weight of 42,000. It accounts for about 25% of the total mass of muscle protein. In the presence of magnesium cations, actin undergoes noncovalent polymerization to form an insoluble filament in the form of a helix, called F-actin. Both forms of actin do not have enzymatic activity. Each G-actin molecule is capable of binding one calcium ion, which plays an important role in initiating contraction. In addition, the G-actin molecule tightly binds one molecule of ATP or ADP. The binding of ATP by G-actin is usually accompanied by its polymerization with the formation of F-actin and the simultaneous cleavage of ATP to ADP and phosphate. ADP remains bound to fibrillar actin.
Tropomyosin is a structural protein of the actin filament, which is an elongated molecule in the form of a cord. Its two polypeptide chains seem to wrap around actin filaments. At the ends of each tropomyosin molecule there are proteins of the troponin system, the presence of which is characteristic of striated muscles.
Troponin is an actin filament regulatory protein. It consists of three subunits: TnT, Tnl and TnS. Troponin T (TnT) mediates the binding of these proteins to tropomyosin. Troponin I (Tnl) blocks (inhibits) the interaction of actin with myosin. Troponin C (TnC) is a calcium-binding protein with a structure and function similar to the widely occurring naturally occurring protein calmodulin. Troponin C, like calmodulin, binds four calcium ions per protein molecule and has a molecular weight of 17,000. In the presence of calcium, the conformation of troponin C changes, which leads to a change in the position of Tn in relation to actin, resulting in the opening of the center of interaction between actin and myosin.
Thus, the thin filament of the striated muscle myofibril consists of F-actin, tropomyosin and three troponin components. In addition to these proteins, the protein actin is involved in muscle contraction. It is found in the Z-line zone, to which the ends of the F-actin molecules of the thin filaments of myofibrils are attached.
Proteins (polypeptides, proteins) are high-molecular substances that contain alpha-amino acids connected by a peptide bond. The composition of proteins is determined in living organisms by the genetic code. Typically, a set of 20 standard amino acids is used during synthesis.
Protein classification
Proteins are separated according to different criteria:
- Molecule shape.
- Composition.
- Functions.
According to the last criterion, proteins are classified:
- To structural ones.
- Nutritious and spare.
- Transport.
- Contractile.
Structural proteins
These include elastin, collagen, keratin, fibroin. Structural polypeptides are involved in the formation of cell membranes. They can create channels in them or perform other functions.
Nutritious, storage proteins
The nutritional polypeptide is casein. Due to it, the growing body is provided with calcium, phosphorus and amino acids.
Seed proteins are reserve proteins cultivated plants, egg white. They are consumed during the embryonic development stage. In the human body, as in animals, proteins are not stored in reserve. They must be regularly obtained from food, otherwise dystrophy is likely to develop.
Transport polypeptides
A classic example of such proteins is hemoglobin. Other polypeptides involved in the movement of hormones, lipids and other substances are also found in the blood.
Cell membranes contain proteins that have the ability to transport ions, amino acids, glucose and other compounds across the cell membrane.
Contractile proteins
The functions of these polypeptides are related to the functioning of muscle fibers. In addition, they ensure the movement of cilia and flagella in protozoa. Contractile proteins perform the function transport of organelles within the cell. Due to their presence, a change in cellular forms is ensured.
Examples of contractile proteins are myosin and actin. It is worth saying that these polypeptides are found not only in muscle fiber cells. Contractile proteins perform their tasks in almost all
Peculiarities
An individual polypeptide, tropomyosin, is found in cells. Contractile muscle protein myosin is its polymer. It forms a complex with actin.
Contractile proteins of muscles do not dissolve in water.
Rate of polypeptide synthesis
It is regulated by the thyroid and steroid hormones. Penetrating into the cell, they bind to specific receptors. The formed complex penetrates and binds to chromatin. Due to this, the rate of polypeptide synthesis at the gene level increases.
Active genes ensure increased synthesis of certain RNA. It leaves the nucleus, goes to ribosomes and activates the synthesis of new structural or contractile proteins, enzymes or hormones. This is the anabolic effect of genes.
Meanwhile protein synthesis in cells the process is quite slow. It requires big energy costs and plastic material. Accordingly, hormones are not able to quickly control metabolism. Their key task is to regulate the growth, differentiation and development of cells in the body.
Muscle contraction
It is bright example of the contractile function of proteins. In the course of research, it was found that the basis for muscle contraction is a change physical properties polypeptide.
Contractile protein actomyosin interacting with adenosine triphosphoric acid. This connection is accompanied by contraction of myofibrils. This interaction can be observed outside the body.
For example, if a solution of adenosine triphosphate is applied to muscle fibers soaked in water (macerated), lacking excitability, they will begin to sharply contract, similar to the contraction of living muscles. This experience has the most important practical significance. It proves the fact that muscle contraction requires chemical reaction contractile proteins with a substance rich in energy.
Effect of vitamin E
On the one hand, it is the main intracellular antioxidant. Vitamin E protects fats and other easily oxidized compounds from oxidation. At the same time, it acts as an electron carrier and participates in redox reactions that are associated with the storage of released energy.
Vitamin E deficiency causes muscle tissue atrophy: contents contractile protein myosin decreases sharply and is replaced by collagen, an inert polypeptide.
Myosin specificity
It is considered one of the key contractile proteins. It accounts for about 55% of general content polypeptides in muscle tissue.
Myosin consists of filaments (thick threads) of myofibrils. The molecule contains a long fibrillar part with a double-helix structure and heads (globular structures). Myosin consists of 6 subunits: 2 heavy and 4 light chains, located in the globular part.
The main task of the fibrillar region is the ability to form bundles of myosin filaments or thick protofibrils.
The heads contain the active site of ATPase and the actin-binding center. Due to this, ATP hydrolysis and communication with actin filaments is ensured.
Varieties
Subtypes of actin and myosin are:
- Dynein of flagella and cilia of protozoa.
- Spectrin in erythrocyte membranes.
- Neurostenin of perisynaptic membranes.
Varieties of actin and myosin also include bacterial polypeptides responsible for the movement various substances c This process is also called chemotaxis.
The role of adenosine triphosphoric acid
If you place actomyosin filaments in an acid solution and add potassium and magnesium ions, you can see that they shorten. In this case, ATP breakdown is observed. This phenomenon indicates that the breakdown of adenosine triphosphoric acid has a definite connection with changes in the physicochemical properties of the contractile protein and, consequently, with muscle function. This phenomenon was first identified by Szent-Gyorgyi and Engelhardt.
The synthesis and breakdown of ATP are of utmost importance in the process of converting chemical energy into mechanical energy. During the breakdown of glycogen, accompanied by the production of lactic acid, as well as during the dephosphorylation of adenosine triphosphoric and creatine phosphoric acids, the participation of oxygen is not required. This explains the ability of an isolated muscle to function under anaerobic conditions.
In muscle fibers that are tired when working in an anaerobic environment, lactic acid and products formed during the breakdown of adenosine triphosphoric and creatine phosphoric acids accumulate. As a result, reserves of substances are exhausted, the breakdown of which releases the necessary energy. If you place a tired muscle in an environment containing oxygen, it will consume it. Some lactic acid will begin to oxidize. As a result, water and carbon dioxide. The released energy will be used for the resynthesis of creatine phosphoric acid, adenosine triphosphoric acid and glycogen from breakdown products. Due to this, the muscle will again gain the ability to work.
Skeletal muscle
Individual properties of polypeptides can only be explained by the example of their functions, that is, their contribution to complex activities. Among the few structures for which a correlation between protein and organ functions has been established, skeletal muscle deserves special attention.
Its cell is activated by nerve impulses (membrane-directed signals). In molecular terms, contraction is based on the cyclic formation of cross-bridges due to periodic interactions between actin, myosin and Mg-ATP. Calcium-binding proteins and Ca ions act as intermediaries between effectors and nerve signals.
Mediation limits the rate of response to on/off impulses and prevents spontaneous contractions. At the same time, some oscillations (fluctuations) of the flywheel muscle fibers winged insects They control not ions or similar low-molecular compounds, but directly contractile proteins. Due to this, very rapid contractions are possible, which, after activation, proceed independently.
Liquid crystal properties of polypeptides
During shortening, the period of the lattice formed by protofibrils changes. When a lattice of thin filaments enters a structure of thick elements, tetragonal symmetry is replaced by hexagonal one. This phenomenon can be considered a polymorphic transition in a liquid crystal system.
Features of mechanochemical processes
They come down to the transformation of chemical energy into mechanical energy. ATPase activity of mitochondrial cell membranes is similar to the activity of the iosin system of skeletal muscles. Common features are also noted in their mechanochemical properties: they contract under the influence of ATP.
Therefore, a contractile protein must be present in the mitochondrial membranes. And he really is there. It has been established that contractile polypeptides are involved in mitochondrial mechanochemistry. However, it also turned out that phosphatidylinositol (a membrane lipid) also plays a significant role in the processes.
Additionally
The myosin protein molecule not only promotes the contraction of various muscles, but can also participate in other intracellular processes. We are talking, in particular, about the movement of organelles, the attachment of actin filaments to membranes, the formation and functioning of the cytoskeleton, etc. Almost always, the molecule interacts in one way or another with actin, which is the second key contractile protein.
It has been proven that actomyosin molecules can change length under the influence of chemical energy released when a phosphoric acid residue is removed from ATP. In other words, it is this process that causes muscle contraction.
The ATP system thus acts as a kind of accumulator of chemical energy. As needed, it turns directly into mechanical through the mediation of actomyosin. In this case, there is no intermediate stage characteristic of the processes of interaction of other elements - the transition to thermal energy.
ACTIN
one of the main proteins will be reduced. muscle fiber elements. It can exist in the form of a monomer (G-A., mol. wt. approx. 42 thousand) and in polymerization. condition (F-A.).
Molecule G-A. has a globular two-domain form and is associated with one ATP molecule, which is converted into adenosine diphosphate during the polymerization of G-A. In salt-free water solutions G-A. did not polymerize. In the case of adding KS1 or MgCl 2, the process begins at a concentration of resp. 0.1-0.15 or 0.01 M. Possibility of polymerization of G-A. in the body depends on actin-binding proteins, for example. filamin, actinin.
FA is a linear polymer that forms a flat helix (its threads are polar) with a pitch of 38 nm and a subunit diameter of 5.5 nm. One turn of the spiral contains 13-14 molecules G-A. Polymerization of the monomer leads to a sharp increase in the viscosity of the solution. F. forms a complex with others. protein - myosin - and has a strong activating effect on its adenosine triphosphatase. An important property of FA is the ability to coordinate metabolic processes, which manifests itself during its interaction. with a number of enzymes (phosphorylase kinase, aldolase, glyceraldehyde-3-phosphate dehydrogenase, etc.).
A. is present in all eukaryotic cells (10-15% by weight of all proteins). In non-muscle cells, it forms the “cytoskeleton” (microfilaments of the cell cytoplasm).
Lit.: Fundamentals of biochemistry, trans. from English, vol. 3, M., 1981, p. 1406-10. B. F. Poglazov.
Chemical encyclopedia. - M.: Soviet Encyclopedia. Ed. I. L. Knunyants. 1988 .
Synonyms:See what "ACTIN" is in other dictionaries:
Actin is a protein, the polymerized form of which forms microfilaments, one of the main components of the cytoskeleton of eukaryotic cells. Together with the protein myosin, it forms the main contractile elements of actomyosin muscles... ... Wikipedia
Actin(s)- * actin(s) * actin(s) is a protein of muscle fibers with an MW of 42 kDa, existing in two forms, fibrillar (actin) and globular (actin). A. has sections complementary to sections of myosin molecules (see), and is part of the main actomyosin... ... Genetics. encyclopedic Dictionary
Muscle fiber protein. Mol. m. 42,000. Two forms: globular (GA) and fibrillar (FA), edges are formed during the polymerization of GA in the presence of ATP and Mg + + ions. On each molecule of A. there are sections complementary to certain sections on ... Biological encyclopedic dictionary
A protein whose fibrillar form forms with myosin the main contractile element of muscles, actomyosin... Big Encyclopedic Dictionary
ACTIN, a muscle fiber protein involved in contractile processes in the cell. Contained primarily in muscle tissue cells; reacting with myosin to form ACTOMYOSIN... Scientific and technical encyclopedic dictionary
Noun, number of synonyms: 1 protein (99) ASIS Dictionary of Synonyms. V.N. Trishin. 2013… Synonym dictionary
actinidia- the name of the female family... Spelling dictionary of Ukrainian language
actin- A periodically contracting protein found inside a eukaryotic cell. Biotechnology topics EN actin... Technical Translator's Guide
Muscle fiber protein. Molecular weight is about 70,000. It exists in two forms: globular (G actin) and fibrillar (F actin), which is a product of polymerization of G actin. In resting muscle, A. is in the form of F actin, forming... ... Great Soviet Encyclopedia
A protein whose fibrillar form forms with myosin the main contractile element of muscles, actomyosin. * * * ACTIN ACTIN, a protein whose fibrillar form forms with myosin the main contractile element of muscles, actomyosin... encyclopedic Dictionary
Actin actin. Muscle fiber protein (molecular weight 42 kDa), exists in two forms, fibrillar and globular, has sections complementary to sections of myosin molecules
the mechanical function is performed by protein: hemoglobin, myosin, collagen, melanin, or insulin??? and got the best answer
Answer from Polina Feigina[guru]
1. Polymer is a high-molecular compound, a substance with a large molecular weight (from several thousand to several million), in which atoms connected by chemical bonds form linear or branched chains, as well as spatial three-dimensional structures. Often in its structure one can distinguish a monomer - a repeating structural fragment that includes several atoms. A polymer is formed from monomers through polymerization. Polymers include numerous natural compounds: proteins, nucleic acids, polysaccharides, rubber and other organic substances. In most cases, the concept refers to organic compounds, however, there are also many inorganic polymers. A large number of polymers are obtained synthetically based on the simplest compounds of elements of natural origin through polymerization reactions, polycondensation and chemical transformations.
Special mechanical properties:
elasticity - the ability to undergo high reversible deformations under a relatively small load (rubbers);
low fragility of glassy and crystalline polymers (plastics, organic glass) ;
the ability of macromolecules to orient under the influence of a directed mechanical field (used in the manufacture of fibers and films).
Features of polymer solutions:
high solution viscosity at low polymer concentration;
The dissolution of the polymer occurs through the swelling stage.
Special chemical properties:
the ability to dramatically change one's physical and mechanical properties under the influence of small quantities of a reagent (vulcanization of rubber, tanning of leather, etc.).
The special properties of polymers are explained not only by their large molecular weight, but also by the fact that macromolecules have a chain structure and have a unique property for inanimate nature - flexibility.
2. Proteins are complex high-molecular natural compounds built from amino acids. Proteins contain 20 different amino acids, which means there is a huge variety of proteins with different combinations of amino acids. Just as we can form an infinite number of words from 33 letters of the alphabet, we can form an infinite number of proteins from 20 amino acids. There are up to 100,000 proteins in the human body.
Proteins are divided into proteins (simple proteins) and proteids (complex proteins).
The number of amino acid residues included in the molecules is different: insulin - 51, myoglobin - 140. Hence Mr protein from 10,000 to several million.
The functions of proteins in the body are varied. They are largely due to the complexity and diversity of the forms and composition of the proteins themselves. Proteins are essential construction material. One of the most important functions of protein molecules is plastic. All cell membranes contain a protein, the role of which is varied. The amount of protein in the membranes is more than half the mass.
Many proteins have a contractile function. These are primarily the proteins actin and myosin, which are part of the muscle fibers of higher organisms. Muscle fibers - myofibrils - are long thin filaments consisting of parallel thinner muscle filaments surrounded by intracellular fluid. It contains dissolved adenosine triphosphoric acid (ATP), which is necessary for contraction, glycogen - nutrient, inorganic salts and many other substances, in particular calcium.
The role of proteins in the transport of substances in the body is great. Having different functional groups and a complex macromolecule structure, proteins bind and transport many compounds through the bloodstream. This is primarily hemoglobin, which carries oxygen from the lungs to the cells. In muscles, this function is taken over by another transport protein - myoglobin.
Another function of protein is storage. Storage proteins include ferritin - iron, ovalbumin - egg protein, casein - milk protein, zein - corn seed protein.
The regulatory function is performed by hormone proteins.
Hormones are biologically active substances that affect metabolism. Many