In the body the role of proteins is extremely high. This is the name of the substance may wear only once becomes a predetermined structure. Up until this moment, the polypeptide, only the amino acid chain, that can perform inherent functions. In General, the spatial structure of proteins (primary, secondary, tertiary, and domain) three – dimensional structure. And the most important for the body secondary, tertiary, and domain structure.
Prerequisites for the study of protein structure
Among the methods for studying the structure of chemical substances plays an important role x-ray crystallography. Through it you can get information about the sequence of atoms in molecular compounds and their spatial organization. Simply put, an x-ray can be done for individual molecules, made possible in the 30-ies of XX century.
It was then that the researchers found that many proteins are not only linear, but can be placed in the spirals, balls and domains. And as a result of mass scientific experiments revealed that the secondary structure of a protein is the final form for the structural proteins and intermediates to enzymes and immunoglobulins. This means that substances which will eventually have a tertiary or Quaternary structure, at the stage of its maturation must undergo a stage of spiraleobraznye inherent secondary structure.
The formation of secondary protein structure
Once completed the synthesis of a polypeptide on the ribosomes of the rough network cell endoplasm, begins to form the secondary structure of the protein. The polypeptide consists of a long molecule, which occupies much space and is inconvenient for transport and execution of integrated functions. Therefore, with the aim of reducing its size and giving it special properties develops secondary structure. This occurs by formation of alpha-helix and beta-layers. Thus, protein secondary structure, which in the future will either turn into tertiary and Quaternary, or will be used in this form.
The organization of the secondary structure
As shown by numerous studies, the secondary structure of the protein consists of either alpha-helix or beta-layer, or alternating sections of these elements. Moreover, the secondary structure is a way of twisting and spiraleobraznye protein molecule. It is a chaotic process which is due to hydrogen bonds that occur between polar portions of the amino acid residues in the polypeptide.
The alpha helix secondary structure
Since the biosynthesis of polypeptides involves only L-amino acids, the formation of protein secondary structure starts with tightening of the spiral in a clockwise direction (right turn). Each spiral coil has to be strictly the 3.6 amino acid residues, and the distance along the helical axis is 0.54 nm. It General properties for the secondary structure of the protein, which do not depend on the type of amino acids involved in the synthesis.
It is determined that not all polypeptide chain spiralized completely. In its structure there are linear plots. In particular, the protein molecule of pepsin spiralizatia only 30%, lysozyme is at 42%, and the hemoglobin is 75%. This means that the secondary structure of a protein is not strictly spiral, and combining it with linear plots or layered.
Beta-layer of the secondary structure
The second type of structural organization of matter is the beta layer, which consists of two or more polypeptide strands connected by hydrogen bond. The latter occurs between free CO NH2 groups. Thus connected, mainly, structural (muscle) proteins.
Protein structure of this type is that a single strand polypeptide with the designation of the end sections A-b is parallel along the other. The only caveat is that the second molecule is antiparallel and is denoted as A. thus, there is a beta-layer, which can consist of as many of the large number of polypeptide chains connected by multiple hydrogen bonds.
The secondary structure of the protein – linkage based on multiple polar interactions of atoms with different indices of electronegativity. Greatest ability to form this connection, I have 4 elements: fluorine, oxygen, nitrogen and hydrogen. Proteins are present in all except fluoride. Because a hydrogen bond can be formed and formed, giving the opportunity to connect polypeptide chains in the beta-layer and in the alpha-helix.
The most easy to explain the occurrence of hydrogen bonds on the example of water, which is a dipole. Oxygen carries a strong negative charge, and due to the high polarization of the O-H when hydrogen is considered positive. In this state the molecules are present in a certain environment. And many of them overlap and collide. Then the oxygen from the first water molecule attracts the hydrogen of the other. And so the chain.
Similar processes occur in proteins: the electronegative oxygen of peptide bonds attracts the hydrogen from any part of another amino acid residue, forming a hydrogen bond. This is a weak polar pairing gap for which you want to spend about 6.3 kJ of energy.
For comparison, the weakest covalent bond in proteins requires 84 kJ of energy in order for her to break. The strongest covalent bond will require 8400 kJ. However, the number of hydrogen bonds in the protein molecule is so huge that their total energy allows the molecule to exist in an aggressive environment and to maintain its spatial structure. Due to this, there are proteins. Protein structure of this type provides strength, which is necessary for the functioning of muscles, bones and ligaments. So huge the value of the secondary structure of proteins for the body.