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 the protein.
The last level in this list is 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. By covalent peptide bonds between the alpha-amino group in one amino acid and the alpha-carboxyl group in another, the molecule is highly stable.
When peptide bonds are formed in cells, the carboxyl group is activated first. After a compound with an amino group occurs. In approximately the same way polypeptide laboratory synthesis is carried out.
The peptide bond, which is a repeating fragment of the polypeptide chain, has a number of features. Under the influence of these features, not only the primary structure of the protein is formed. They affect the higher organizational levels of the polypeptide chain. Among the main distinguishing features are coplanarity (the ability of all atoms that are in the peptide group to be in the same plane), the transport of substituents with respect to the C-N bond, and the property to exist in 2 resonance forms. The features of the peptide bond also include the ability to form hydrogen bonds. Moreover, from each peptide group, two hydrogen bonds can form with other groups (including peptide). 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 effect on the formation of a secondary protein structure. So, in the area where hydroxyproline or proline is located, the peptide chain bends easily, 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 names of the amino acids included in them. A dipeptide gives two amino acids, a tripeptide gives three, a tetrapeptide gives four, and so on. In each polypeptide chain (or peptide) of any length, there is an N-terminal amino acid that contains a free amino group, and a C-terminal amino acid that contains a free carboxyl group.
Properties of proteins.
When studying these compounds, scientists were interested in several questions. Researchers, first of all, sought to determine the size, determine the shape and mass of protein molecules. It should be noted that these were quite complex tasks. The difficulty was that the determination of the relative molecular weight by increasing the boiling point of protein solutions (as is the case with other substances) is impossible, due to the fact that protein solutions cannot be boiled. And the determination of the indicator in accordance with a decrease in the freezing temperature gives inaccurate results. In addition, pure proteins never occur. However, using the developed methods, it was found that the molecular weight ranges from 14 to 45 thousand or more.
One of the important characteristics of the compounds is fractional salting out. This process is the selection of proteins from solutions after the addition of salt solutions with various concentrations.
Another important characteristic is denaturation. This process occurs during the deposition of proteins by heavy metals. Denaturation is a loss of natural properties. This process involves various transformations of the molecule, in addition to breaking the polypeptide chain. In other words, the primary protein structure during denaturation remains unchanged.