Primary structure of the protein

The structure of the protein can be represented by one of four options. Each variant has its own peculiarities. So, there is a quaternary, ternary, secondary and primary protein structure.

The last level in this list is a linear polypeptide chain of amino acids. Amino acids are connected with each other by peptide bonds. The primary structure of the protein is the simplest level of organization of the molecule. By means of covalent peptide bonds between the alpha-amino group in one amino acid and the alpha-carboxyl group in another, a high stability of the molecule is provided.

When the peptide bonds are formed in the cells, the carboxyl group is first activated. After that, there is a connection with the amino group. Similarly, polypeptide laboratory synthesis is carried out.

The peptide bond, which is a repeating fragment of the polypeptide chain, has a number of characteristics. Under the influence of these features, not only the primary structure of the protein is formed. They also affect the higher organizational levels of the polypeptide chain. Among the main distinguishing features are the coplanarity (the ability of all atoms that enter the peptide group to be in the same plane), the transposition of substituents relative to the C-N bond, the property to exist in 2 resonance forms. The specific features of peptide bonding include the ability to form hydrogen bonds. In this case, from each peptide group, two hydrogen bonds can be formed with other groups (peptide including). 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 is easily bent, due to the fact that there is no second hydrogen bond that would hold it (as usual).

The name of peptides is formed from the names of the amino acids included in them. A dipeptide produces two amino acids, a tripeptide is three, a tetrapeptide is four, and so on. Each polypeptide chain (or peptide) of any length contains an N-terminal amino acid in which a free amino group is present and a C-terminal amino acid in which a free carboxyl group is present.

Properties of proteins.

When studying these compounds, scientists were interested in several questions. The researchers, first of all, sought to determine the size, determine the shape and mass of protein molecules. It should be noted that these were rather complicated tasks. The difficulty was that it is impossible to determine the relative molecular weight by increasing the boiling point of protein solutions (as is done with other substances), since protein solutions can not be boiled. A definition of the indicator in accordance with the lowering of the freezing point results in inaccurate results. In addition, proteins in pure form never occur. However, with the help of the developed methods it was established that the molecular mass varies between 14 and 45 thousand and more.

One of the important characteristics of compounds is fractional salting out. This process is the isolation of proteins from solutions after the addition of brine solutions with different concentrations.

Another important characteristic is denaturation. This process occurs when proteins are precipitated with heavy metals. Denaturation is a loss of natural properties. This process involves different transformations of the molecule, except for the breakdown of the polypeptide chain. In other words, the primary structure of the protein remains unchanged during denaturation.