The process of protein biosynthesis is extremely important for the cell. Since proteins are complex substances that play a major role in tissues, they are indispensable. For this reason, a whole chain of protein biosynthesis processes is realized in the cell, which takes place in several organelles. This guarantees the cell reproduction and the possibility of existence.
The essence of the process of protein biosynthesis
The only site for protein synthesis is the rough endoplasmic reticulum. Here is located the bulk of the ribosomes, which are responsible for the formation of the polypeptide chain. However, before the translation stage (the process of protein synthesis) begins, activation of the gene, which stores information about the protein structure, is required. After that, copying of this section of DNA (or RNA, if bacterial biosynthesis is considered) is required.
After copying DNA, the process of creating messenger RNA is required. Based on it, the synthesis of the protein chain will be performed. Moreover, all stages that occur with the involvement of nucleic acids must occur in the cell nucleus. However, this is not where protein synthesis takes place. This islocation where preparations for biosynthesis are carried out.
Ribosomal protein biosynthesis
The main site where protein synthesis occurs is the ribosome, a cell organelle consisting of two subunits. There are a huge number of such structures in the cell, and they are mainly located on the membranes of the rough endoplasmic reticulum. The biosynthesis itself occurs as follows: the messenger RNA formed in the nucleus of the cell exits through the nuclear pores into the cytoplasm and meets with the ribosome. Then the mRNA is pushed into the gap between the subunits of the ribosome, after which the first amino acid is fixed.
To the place where protein synthesis occurs, amino acids are supplied with the help of transfer RNA. One such molecule can bring one amino acid at a time. They join in turn, depending on the codon sequence of messenger RNA. Also, synthesis may stop for a while.
When moving along the mRNA, the ribosome can enter areas (introns) that do not code for amino acids. In these places, the ribosome simply moves along the mRNA, but no amino acids are added to the chain. As soon as the ribosome reaches the exon, that is, the site that codes for the acid, then it reattaches to the polypeptide.
Postsynthetic modification of proteins
After the ribosome reaches the stop codon of messenger RNA, the process of direct synthesis is completed. However, the resulting molecule has a primary structure and cannot yet perform the functions reserved for it. In order to fully function, the moleculeshould be organized into a certain structure: secondary, tertiary or even more complex - quaternary.
Structural organization of protein
Secondary structure - the first stage of structural organization. To achieve it, the primary polypeptide chain must coil (form alpha helices) or fold (create beta layers). Then, in order to take up even less space along the length, the molecule is even more contracted and coiled into a ball due to hydrogen, covalent and ionic bonds, as well as interatomic interactions. Thus, the globular structure of the protein is obtained.
Quadternary protein structure
The quaternary structure is the most complex of all. It consists of several sections with a globular structure, connected by fibrillar filaments of the polypeptide. In addition, the tertiary and quaternary structure can contain a carbohydrate or lipid residue, which expands the spectrum of protein functions. In particular, glycoproteins, complex compounds of protein and carbohydrate, are immunoglobulins and perform a protective function. Also, glycoproteins are located on cell membranes and work as receptors. However, the molecule is modified not where protein synthesis occurs, but in the smooth endoplasmic reticulum. Here there is the possibility of attaching lipids, metals and carbohydrates to protein domains.
