Amino acids in the polypeptide chain are linked by an amide bond, which is formed between the α-carboxyl group of one and the α-amino group of the next amino acid (Fig. 1). The covalent bond formed between amino acids is called peptide bond. The oxygen and hydrogen atoms of the peptide group in this case occupy a transposition.
Rice. 1. Scheme of peptide bond formation.In each protein or peptide, one can distinguish: N-terminus a protein or peptide that has a free a-amino group (-NH2);
S-endhaving a free carboxyl group (-COOH);
Peptide backboneproteins, consisting of repeating fragments: -NH-CH-CO-; Amino acid radicals(side chains) (R1 And R2)- variable groups.
The abbreviated notation of the polypeptide chain, as well as protein synthesis in cells, necessarily begins at the N-terminus and ends at the C-terminus:
The names of the amino acids included in the peptide and forming a peptide bond have the endings -ill. For example, the tripeptide above is called threonyl-histidyl-proline.
The only variable part that distinguishes one protein from all the others is the combination of radicals (side chains) of the amino acids that make up it. Thus, the individual properties and functions of a protein are determined by the structure and sequence of amino acids in the polypeptide chain.
Polypeptide chains of various body proteins can include from a few amino acids to hundreds and thousands of amino acid residues. Their molecular weight (molecular weight) also varies widely. So, the hormone vasopressin consists of 9 amino acids, they say. mass 1070 kD; insulin - from 51 amino acids (in 2 chains), they say. mass 5733 kD; lysozyme - from 129 amino acids (1 chain), they say. mass 13 930 kD; hemoglobin - from 574 amino acids (4 chains), they say. mass 64,500 kD; collagen (tropocollagen) - from about 1000 amino acids (3 chains), they say. mass ~130,000 kD.
The properties and function of a protein depend on the structure and order of alternation of amino acids in the chain, a change in the amino acid composition can greatly change them. So, 2 hormones of the posterior pituitary gland - oxytocin and vasopressin - are nanopeptides and differ in 2 of 9 amino acids (in positions 3 and 8):
The main biological effect of oxytocin is to stimulate the contraction of the smooth muscles of the uterus during childbirth, and vasopressin causes water reabsorption in the renal tubules (antidiuretic hormone) and has a vasoconstrictive property. Thus, despite the great structural similarity, the physiological activity of these peptides and the target tissue they act on differ, i.e. replacement of only 2 of 9 amino acids causes a significant change in the function of the peptide.
Sometimes a very small change in the structure of a large protein causes suppression of its activity. So, the enzyme alcohol dehydrogenase, which breaks down ethanol in the human liver, consists of 500 amino acids (in 4 chains). Its activity among the inhabitants of the Asian region (Japan, China, etc.) is much lower than among the inhabitants of Europe. This is due to the fact that in the polypeptide chain of the enzyme, glutamic acid is replaced by lysine at position 487.
Interactions between amino acid radicals play great importance in the stabilization of the spatial structure of proteins, 4 types of chemical bonds can be distinguished: hydrophobic, hydrogen, ionic, disulfide.
Hydrophobic bonds arise between nonpolar hydrophobic radicals (Fig. 2). They play a leading role in the formation of the tertiary structure of the protein molecule.
Rice. 2. Hydrophobic interactions between radicals
Hydrogen bonds- are formed between polar (hydrophilic) uncharged groups of radicals having a mobile hydrogen atom, and groups with an electronegative atom (-O or -N-) (Fig. 3).
Ionic bonds are formed between polar (hydrophilic) ionic radicals having oppositely charged groups (Fig. 4).
Rice. 3. Hydrogen bonds between amino acid radicals
Rice. 4. Ionic bond between lysine and aspartic acid radicals (A) and examples of ionic interactions (B)
disulfide bond- covalent, formed by two sulfhydryl (thiol) groups of cysteine radicals located in different places of the polypeptide chain (Fig. 5). It is found in proteins such as insulin, the insulin receptor, immunoglobulins, etc.
Disulfide bonds stabilize spatial structure one polypeptide chain or link 2 chains together (for example, chains A and B of the insulin hormone) (Fig. 6).
Rice. 5. Formation of a disulfide bond.
Rice. 6. Disulfide bonds in the insulin molecule. Disulfide bonds: between cysteine residues of the same chain A(a), between chains A And IN(b). Numbers - position of amino acids in polypeptide chains.
By Masterweb
21.07.2018 17:00A peptide bond is a strong connection between fragments of two amino acids, which underlies the formation of linear structures of proteins and peptides. In such molecules, each amino acid (with the exception of the terminal ones) is connected to the previous and subsequent ones.
Depending on the number of links, peptide bonds can create dipeptides (consist of two amino acids), tripeptides (of three), tetrapeptides, pentapeptides, etc. Short chains (from 10 to 50 monomers) are called oligopeptides, and long chains are called polypeptides and proteins ( mol weight more than 10 thousand Yes).
Characterization of the peptide bond
A peptide bond is a covalent chemical compound between the first carbon atom of one amino acid and the nitrogen atom of another, resulting from the interaction of the alpha carboxyl group (COOH) with the alpha amino group (NH2). In this case, the nucleophilic substitution of OH-hydroxyl for an amino group occurs, from which hydrogen is separated. As a result, a single C-N bond and a water molecule are formed.
Since the loss of some components (OH group and hydrogen atom) occurs during the reaction, peptide units are no longer called amino acids, but amino acid residues. Due to the fact that the latter contain 2 carbon atoms, the peptide chain is alternating C-C and C-N bonds that form the peptide backbone. On the sides of it are amino acid radicals. The distance between carbon and nitrogen atoms varies from 0.132 to 0.127 nm, which indicates an indefinite bond.
A peptide bond is a very strong type of chemical interaction. Under standard biochemical conditions corresponding to the cellular environment, it does not undergo self-destruction.
The peptide bond of proteins and peptides is characterized by the property of coplanarity, since all the atoms involved in its formation (C, N, O and H) are located in the same plane. This phenomenon is explained by the rigidity (i.e., the impossibility of rotation of the elements around the bond) resulting from resonance stabilization. Within the amino acid chain, between the planes of the peptide groups, there are α-carbon atoms associated with radicals.
Configuration types
Depending on the position of the alpha carbon atoms relative to the peptide bond, the latter can have 2 configurations:
- "cis" (located on one side);
- "trans" (located on different sides).
The trans form is characterized by greater stability. Sometimes configurations are characterized by the arrangement of radicals, which does not change the essence, since they are associated with alpha carbon atoms.
Resonance phenomenon
The peculiarity of the peptide bond is that it is 40% double and can be found in three forms:
- Ketolic (0.132 nm) - C-N-bond is stabilized and completely single.
- Transitional or mesomeric - an intermediate form, has a partially indefinite character.
- Enol (0.127 nm) - the peptide bond becomes completely double, and C-O connection- completely single. In this case, oxygen acquires a partially negative charge, and the hydrogen atom acquires a partially positive charge.
This feature is called the resonance effect and is explained by the delocalization covalent bond between carbon and nitrogen. In this case, the hybrid sp2 orbitals form an electron cloud that propagates to the oxygen atom.
Peptide bond formation
Peptide bond formation is a typical polycondensation reaction that is thermodynamically unfavorable. Under natural conditions, the equilibrium is shifted towards free amino acids, therefore, for the implementation of the synthesis, a catalyst is required that activates or modifies the carboxyl group for easier leaving of the hydroxyl group.
In a living cell, the formation of a peptide bond occurs in the protein-synthesizing center, where specific enzymes act as a catalyst, working with the expenditure of energy from macroergic bonds.
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(1) and (2) a dipeptide (a chain of two amino acids) and a water molecule are formed. According to the same scheme, the ribosome also generates longer chains of amino acids: polypeptides and proteins. The different amino acids that are the "building blocks" of a protein differ in the R radical.
Peptide bond properties
As in the case of any amides, in a peptide bond, due to the resonance of canonical structures, the C-N bond between the carbonyl group carbon and the nitrogen atom partially has a double character:
This is manifested, in particular, in a decrease in its length to 1.33 angstroms:
This gives rise to the following properties:
- 4 bond atoms (C, N, O and H) and 2 α-carbons are in the same plane. R-groups of amino acids and hydrogens at α-carbons are outside this plane.
- H And O in the peptide bond, as well as the α-carbons of two amino acids are transoriented (the trans-isomer is more stable). In the case of L-amino acids, which occurs in all natural proteins and peptides, the R-groups are also transoriented.
- Rotation around the C-N bond is difficult, rotation around the C-C bond is possible.
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See what the "Peptide bond" is in other dictionaries:
-(CONH) chemical bond, connecting the amino group of one amino acid with the carboxyl group of another in the molecules of peptides and proteins ... Big Encyclopedic Dictionary
peptide bond- - amide bond (NHCO), formed between the amino and carboxyl groups of amino acids as a result of the dehydration reaction ... Concise Dictionary biochemical terms
peptide bond- Covalent bond between the alpha amino group of one amino acid and the alpha carboxyl group of another amino acid Biotechnology topics EN peptide bond … Technical Translator's Handbook
Peptide bond- * peptide bond * peptide bond a covalent bond between two amino acids resulting from the combination of the α amino group of one molecule with the α carboxyl group of another molecule, while removing water ... Genetics. encyclopedic Dictionary
PEPTIDE BOND- chem. CO NH bond, characteristic of amino acids in protein and peptide molecules. P. s. found in some others. organic compounds. During its hydrolysis, a free carboxyl group and an amino group are formed ... Great Polytechnic Encyclopedia
Type of amide bond; arises as a result of the interaction of the amino group (NH2) of one amino acid with? carboxyl group (COOH) other amino acids. The C (O) NH group in proteins and peptides is in a state of keto-enol tautomerism (the existence of ... ... Biological encyclopedic Dictionary
- (СО NH), a chemical bond that connects the amino group of one amino acid with the carboxyl group of another in peptide and protein molecules. * * * PEPTIDE BOND PEPTIDE BOND (CO NH), a chemical bond that connects the amino group of one amino acid ... ... encyclopedic Dictionary
Peptide bond A kind of amide bond, formed between the α carboxyl and α amino groups of two amino acids. (
Peptide bond in its own way chemical nature is covalent and gives high strength to the primary structure of the protein molecule. Being a repeating element of the polypeptide chain and having specific structural features, the peptide bond affects not only the shape of the primary structure, but also higher levels organization of the polypeptide chain.
A great contribution to the study of the structure of the protein molecule was made by L. Pauling and R. Corey. Drawing attention to the fact that the protein molecule has the most peptide bonds, they were the first to conduct painstaking X-ray diffraction studies of this bond. We studied the bond lengths, the angles at which the atoms are located, the direction of the arrangement of atoms relative to the bond. Based on the research, the following main characteristics of the peptide bond were established.
1. Four atoms of the peptide bond (C, O, N, H) and two attached
a-carbon atoms lie in the same plane. The R and H groups of a-carbon atoms lie outside this plane.
2. O and H atoms of the peptide bond and two a-carbon atoms, as well as R-groups, have a trans orientation relative to the peptide bond.
3. The C–N bond length of 1.32 Å is intermediate between the length of a double covalent bond (1.21 Å) and a single covalent bond (1.47 Å). Hence it follows that the C–N bond has a partially unsaturated character. This creates the prerequisites for the implementation of tautomeric rearrangements at the site of the double bond with the formation of the enol form, i.e. the peptide bond may exist in the keto-enol form.
Rotation around the –C=N– bond is difficult, and all atoms in the peptide group have a planar trans configuration. The cis configuration is energetically less favorable and occurs only in some cyclic peptides. Each planar peptide fragment contains two bonds to rotatable a-carbon atoms.
There is a very close relationship between the primary structure of a protein and its function in a given organism. In order for a protein to perform its characteristic function, a completely specific sequence of amino acids is required in the polypeptide chain of this protein. This specific amino acid sequence, qualitative and quantitative composition is genetically fixed (DNA → RNA → protein). Each protein is characterized by a certain sequence of amino acids, the replacement of at least one amino acid in the protein leads not only to structural rearrangements, but also to changes physical and chemical properties and biological functions. The existing primary structure predetermines the subsequent (secondary, tertiary, quaternary) structures. For example, in erythrocytes healthy people contains protein - hemoglobin with a certain sequence of amino acids. A small part of people have a congenital anomaly in the structure of hemoglobin: their erythrocytes contain hemoglobin, which in one position instead of glutamic acid (charged, polar) contains the amino acid valine (hydrophobic, non-polar). Such hemoglobin significantly differs in physicochemical and biological properties from normal. The appearance of a hydrophobic amino acid leads to the appearance of a “sticky” hydrophobic contact (erythrocytes do not move well in blood vessels), to a change in the shape of an erythrocyte (from biconcave to crescent-shaped), as well as to a deterioration in oxygen transfer, etc. Children born with this anomaly die in early childhood from sickle cell anemia.
Comprehensive evidence in favor of the assertion that biological activity is determined by the amino acid sequence was obtained after the artificial synthesis of the enzyme ribonuclease (Merrifield). The synthesized polypeptide with the same amino acid sequence as the natural enzyme had the same enzymatic activity.
Research recent decades showed that the primary structure is fixed genetically, i.e. the sequence of amino acids in a polypeptide chain is determined genetic code DNA, and, in turn, determines the secondary, tertiary and quaternary structures of the protein molecule and its general conformation. The first protein whose primary structure was established was the protein hormone insulin (contains 51 amino acids). This was done in 1953 by Frederick Sanger. To date, the primary structure of more than ten thousand proteins has been deciphered, but this is a very small number, given that there are about 10 12 proteins in nature. As a result of free rotation, polypeptide chains are able to twist (fold) into various structures.
secondary structure. The secondary structure of a protein molecule is understood as a way of laying a polypeptide chain in space. The secondary structure of a protein molecule is formed as a result of one or another type of free rotation around the bonds connecting a-carbon atoms in a polypeptide chain. As a result of this free rotation, polypeptide chains are able to twist (fold) in space into various structures.
Three main types of structure have been found in natural polypeptide chains:
- a-helix;
- β-structure (folded sheet);
- statistical tangle.
The most probable type of structure of globular proteins is considered to be α-helix Twisting occurs clockwise (right helix), which is due to the L-amino acid composition of natural proteins. The driving force in the emergence α-helices is the ability of amino acids to form hydrogen bonds. R-groups of amino acids are directed outward from the central axis a-helices. >С=О and >N–Н dipoles of adjacent peptide bonds are optimally oriented for dipole interaction, resulting in the formation of an extensive system of intramolecular cooperative hydrogen bonds stabilizing the a-helix.
Helix pitch (one full turn) 5.4Å includes 3.6 amino acid residues.
Figure 2 - Structure and parameters of the a-helix of the protein
Each protein is characterized by a certain degree of helicalization of its polypeptide chain.
The spiral structure can be disturbed by two factors:
1) in the presence of a proline residue in the chain, the cyclic structure of which introduces a kink in the polypeptide chain - there is no –NH 2 group, therefore the formation of an intrachain hydrogen bond is impossible;
2) if in the polypeptide chain there are many amino acid residues in a row that have a positive charge (lysine, arginine) or a negative charge (glutamic, aspartic acids), in this case, the strong mutual repulsion of like-charged groups (-COO - or -NH 3 +) significantly exceeds stabilizing effect of hydrogen bonds in a-helices.
Another type of polypeptide chain configuration found in hair, silk, muscle and other fibrillar proteins is called β structures or folded sheet. The folded sheet structure is also stabilized by hydrogen bonds between the same dipoles –NH...... O=C<. Однако в этом случае возникает совершенно иная структура, при которой остов полипептидной цепи вытянут таким образом, что имеет зигзагообразную структуру. Складчатые участки полипептидной цепи проявляют кооперативные свойства, т.е. стремятся расположиться рядом в белковой молекуле, и формируют параллельные
identically directed polypeptide chains or antiparallel,
which are strengthened by hydrogen bonds between these chains. Such structures are called b-folded sheets (Figure 2).
Figure 3 - b-structure of polypeptide chains
a-Helix and folded sheets are ordered structures, they have a regular arrangement of amino acid residues in space. Some sections of the polypeptide chain do not have any regular periodic spatial organization, they are designated as random or statistical tangle.
All these structures arise spontaneously and automatically due to the fact that a given polypeptide has a specific amino acid sequence that is genetically predetermined. a-helices and b-structures determine a certain ability of proteins to perform specific biological functions. So, the a-helical structure (a-keratin) is well adapted to form external protective structures - feathers, hair, horns, hooves. The b-structure contributes to the formation of flexible and inextensible silk and cobwebs, and the conformation of the collagen protein provides the high tensile strength required for tendons. The presence of only a-helices or b-structures is typical for filamentous (fibrillar) proteins. In the composition of globular (spherical) proteins, the content of a-helices and b-structures and structureless regions varies greatly. For example: insulin spiralized 60%, ribonuclease enzyme - 57%, chicken egg protein lysozyme - 40%.
Tertiary structure. Under the tertiary structure understand the way of laying the polypeptide chain in space in a certain volume.
The tertiary structure of proteins is formed by additional folding of the peptide chain containing a-helix, b-structures and random coil regions. The tertiary structure of a protein is formed completely automatically, spontaneously and completely predetermined by the primary structure and is directly related to the shape of the protein molecule, which can be different: from spherical to threadlike. The shape of a protein molecule is characterized by such an indicator as the degree of asymmetry (the ratio of the long axis to the short one). At fibrillar or filamentous proteins, the degree of asymmetry is greater than 80. When the degree of asymmetry is less than 80, proteins are classified as globular. Most of them have a degree of asymmetry of 3-5, i.e. the tertiary structure is characterized by a fairly dense packing of the polypeptide chain, approaching the shape of a ball.
During the formation of globular proteins, non-polar hydrophobic radicals of amino acids are grouped inside the protein molecule, while polar radicals are oriented towards water. At some point, the thermodynamically most favorable stable conformation of the molecule, the globule, arises. In this form, the protein molecule is characterized by a minimum free energy. The conformation of the resulting globule is influenced by such factors as the pH of the solution, the ionic strength of the solution, as well as the interaction of protein molecules with other substances.
The main driving force in the emergence of a three-dimensional structure is the interaction of amino acid radicals with water molecules.
fibrillar proteins. When forming a tertiary structure, they do not form globules - their polypeptide chains do not fold, but remain elongated in the form of linear chains, grouping into fibril fibers.
Drawing – The structure of a collagen fibril (fragment).
Recently, evidence has appeared that the process of formation of the tertiary structure is not automatic, but is regulated and controlled by special molecular mechanisms. This process involves specific proteins - chaperones. Their main functions are the ability to prevent the formation of non-specific (chaotic) random coils from the polypeptide chain, and to ensure their delivery (transport) to subcellular targets, creating conditions for the completion of the folding of the protein molecule.
Stabilization of the tertiary structure is ensured by non-covalent interactions between the atomic groups of side radicals.
Figure 4 - Types of bonds that stabilize the tertiary structure of the protein
A) electrostatic forces attraction between radicals carrying oppositely charged ionic groups (ion-ion interactions), for example, a negatively charged carboxyl group (- COO -) of aspartic acid and (NH 3 +) a positively charged e-amino group of a lysine residue.
b) hydrogen bonds between the functional groups of side radicals. For example, between the OH group of tyrosine and the carboxyl oxygen of aspartic acid
V) hydrophobic interactions due to van der Waals forces between non-polar amino acid radicals. (For example, groups
-CH 3 - alanine, valine, etc.
G) dipole-dipole interactions
e) disulfide bonds(–S–S–) between cysteine residues. This bond is very strong and is not present in all proteins. This connection plays an important role in the protein substances of grain and flour, because. affects the quality of gluten, the structural and mechanical properties of the dough and, accordingly, the quality of the finished product - bread, etc.
A protein globule is not an absolutely rigid structure: within certain limits, reversible movements of parts of the peptide chain relative to each other are possible with the breaking of a small number of weak bonds and the formation of new ones. The molecule, as it were, breathes, pulsates in its different parts. These pulsations do not disturb the basic conformation plan of the molecule, just as thermal vibrations of atoms in a crystal do not change the structure of the crystal unless the temperature is so high that melting occurs.
Only after a protein molecule acquires a natural, native tertiary structure does it show its specific functional activity: catalytic, hormonal, antigenic, etc. It is during the formation of the tertiary structure that the formation of active centers of enzymes, centers responsible for the incorporation of the protein into the multienzyme complex, centers responsible for the self-assembly of supramolecular structures takes place. Therefore, any impact (thermal, physical, mechanical, chemical) that leads to the destruction of this native conformation of the protein (breaking bonds) is accompanied by a partial or complete loss of its biological properties by the protein.
The study of the complete chemical structures of some proteins has shown that in their tertiary structure zones are revealed where the hydrophobic radicals of amino acids are concentrated, and the polypeptide chain is actually wrapped around the hydrophobic core. Moreover, in some cases, two or even three hydrophobic nuclei are isolated in a protein molecule, resulting in a 2 or 3 nuclear structure. This type of molecular structure is characteristic of many proteins with a catalytic function (ribonuclease, lysozyme, etc.). A separate part or region of a protein molecule that has a certain degree of structural and functional autonomy is called a domain. Some enzymes, for example, have distinct substrate-binding and coenzyme-binding domains.
Biologically, fibrillar proteins play a very important role in the anatomy and physiology of animals. In vertebrates, these proteins account for 1/3 of their total content. An example of fibrillar proteins is silk protein - fibroin, which consists of several antiparallel chains with a folded sheet structure. Protein a-keratin contains from 3-7 chains. Collagen has a complex structure in which 3 identical left-handed chains are twisted together to form a right-handed triple helix. This triple helix is stabilized by numerous intermolecular hydrogen bonds. The presence of amino acids such as hydroxyproline and hydroxylysine also contributes to the formation of hydrogen bonds that stabilize the triple helix structure. All fibrillar proteins are poorly soluble or completely insoluble in water, since they contain many amino acids containing hydrophobic, water-insoluble R-groups of isoleucine, phenylalanine, valine, alanine, methionine. After special processing, insoluble and indigestible collagen is converted into a gelatin-soluble mixture of polypeptides, which is then used in the food industry.
Globular proteins. They perform a variety of biological functions. They perform a transport function, i.e. carry nutrients, inorganic ions, lipids, etc. Hormones, as well as components of membranes and ribosomes, belong to the same class of proteins. All enzymes are also globular proteins.
Quaternary structure. Proteins containing two or more polypeptide chains are called oligomeric proteins, they are characterized by the presence of a quaternary structure.
Figure - Schemes of tertiary (a) and quaternary (b) protein structures
In oligomeric proteins, each of the polypeptide chains is characterized by its primary, secondary and tertiary structure, and is called a subunit or protomer. The polypeptide chains (protomers) in such proteins can be either the same or different. Oligomeric proteins are called homogeneous if their protomers are the same and heterogeneous if their protomers are different. For example, the hemoglobin protein consists of 4 chains: two -a and two -b protomers. The a-amylase enzyme consists of 2 identical polypeptide chains. Quaternary structure is understood as the arrangement of polypeptide chains (protomers) relative to each other, i.e. way of their joint stacking and packaging. In this case, the protomers interact with each other not by any part of their surface, but by a certain area (contact surface). The contact surfaces have such an arrangement of atomic groups between which hydrogen, ionic, hydrophobic bonds arise. In addition, the geometry of the protomers also contributes to their connection. Protomers fit together like a key to a lock. Such surfaces are called complementary. Each protomer interacts with the other at multiple points, making it impossible to link to other polypeptide chains or proteins. Such complementary interactions of molecules underlie all biochemical processes in the body.
Able to connect with each other peptide St. (a polymer molecule is formed).
Peptide bond - between the α-carboxyl group of one amino. Andα-amino.other amino..
When naming, add the suffix "-il", the last aminok. not rev. its name.
(alanyl-seryl-tryptophan)
Peptide bond properties
1. Transposition of amino acid radicals with respect to the C-N bond
2. Coplanarity - all atoms in the peptide group are in the same plane, while "H" and "O" are located on opposite sides of the peptide bond.
3. The presence of the keto form (o-c=n) and enol (o=c-t-n) form
4. Ability to form two hydrogen bonds with other peptides
5. The peptide bond has a partially double bond character, the length is less than a single bond, it is a rigid structure, rotation around it is difficult.
For the detection of proteins and peptides - biuret reaction (from blue to purple)
4) PROTEIN FUNCTIONS:
Structural proteins (collagen, keratin),
Enzymatic (pepsin, amylase),
Transport (transferrin, albumin, hemoglobin),
Food (egg proteins, cereals),
Contractile and motor (actin, myosin, tubulin),
Protective (immunoglobulins, thrombin, fibrinogen),
Regulatory (somatotropic hormone, adrenocorticotropic hormone, insulin).
LEVELS OF PROTEIN STRUCTURE ORGANIZATION
Protein - a sequence of amino acids linked to each other peptide bonds.
Peptide - amino. no more than 10
Polypeptide - from 10 to
Protein - more than 40 amino acids.
PRIMARY STRUCTURE -linear protein molecule, image. when combined with amino acids. into the chain.
protein polymorphism- can be inherited and remain in the population
The sequence and ratio of amino acids in the primary structure determines the formation of secondary, tertiary and quaternary structures.
SECONDARY STRUCTURE- interaction pept. groups with arr. hydrogen. connections. There are 2 types of structures - laying in the form of a rope and a pot.
Two variants of the secondary structure: α-helix (α-structure or parallel) and β-pleated layer (β-structure or anti-parallel).
In one protein, as a rule, both structures are present, but in different proportions.
In globular proteins, the α-helix predominates, in fibrillar proteins, the β-structure.
The secondary structure is formed only with the participation of hydrogen bonds between peptide groups: the oxygen atom of one group reacts with the hydrogen atom of the second, while the oxygen of the second peptide group binds to the hydrogen of the third, etc.
