The structure of the protein can be represented by one of four options. Each option has its own features. So, there is a quaternary, ternary, secondary and primary structure of a protein.
The last level in this list representsis a linear polypeptide chain of amino acids. Amino acids are linked to each other by peptide bonds. The primary structure of the protein is the simplest level of organization of the molecule. Through covalent peptide bonds between the alpha-amino group in one amino acid and the alpha-carboxyl group in the other, high stability of the molecule is ensured.
When peptide bonds form in cellsfirst activated carboxyl group. After there is a connection with the amino group. Polypeptide laboratory synthesis is approximately the same.
Peptide bond representinga repeating fragment of a polypeptide chain, has a number of features. Under the influence of these features not only the primary structure of the protein is formed. They also affect higher organizational levels of the polypeptide chain. Among the main distinguishing features are coplanarity (the ability of all atoms that are part of a peptide group to be in the same plane), the transposition of substituents relative to the C – N bond, the ability to exist in 2 resonant forms. The peptide bond also includes the ability to form hydrogen bonds. In addition, two hydrogen bonds with other groups (including peptide groups) can be formed from each peptide group. However, there are exceptions. These include peptide groups with amino groups of hydroxyproline or proline. They can form only one hydrogen bond. This has an impact on the formation of secondary protein structure. So, on the site where hydroxyproline or proline is located, the peptide chain is easily bent, due to the fact that there is no second hydrogen bond that would hold it (as usual).
The name of the peptides is formed from the namesamino acids in them. A dipeptide gives two amino acids, a tripeptide gives three, a tetrapeptide gives four, and so on. Each polypeptide chain (or peptide) of any length contains an N-terminal amino acid containing a free amino group and a C-terminal amino acid in which a free carboxyl group is present.
Properties of proteins.
When studying these compounds, scientists were interested ina few questions. The researchers, above all, sought to find out the size, determine the shape and mass of protein molecules. It should be noted that these were quite complex tasks. The difficulty was that determining the relative molecular weight by increasing the boiling point of protein solutions (as is the case with other substances) is impossible, since protein solutions cannot be boiled. And the definition of the indicator in accordance with the lowering of the freezing temperature results gives inaccurate. In addition, pure proteins are never found. However, using the developed methods, it was found that the molecular weight ranges from 14 to 45 thousand and more.
One of the important characteristics of compounds isfractional salting out. This process is the isolation of proteins from solutions after the addition of salt solutions with different concentrations.
Another important characteristic isdenaturation. This process occurs during the precipitation of proteins with heavy metals. Denaturation is a loss of natural properties. This process involves different transformations of the molecule, except for breaking the polypeptide chain. In other words, the primary structure of the protein during denaturation remains unchanged.
