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 processes of protein biosynthesis is realized in the cell, which proceeds in several organelles. This guarantees cell reproduction and the possibility of existence.
The essence of protein biosynthesis
The only place for protein synthesis is the rough endoplasmic reticulum. Here lies the bulk of the ribosomes that are responsible for the formation of the polypeptide chain. However, before the translation stage begins (the process of protein synthesis), activation of the gene is required, which stores information about the protein structure. After that, copying this section of DNA (or RNA, if bacterial biosynthesis is considered) is required.
After copying the DNA, the process of creating messenger RNA is required. Based on it, protein chain synthesis will be performed. Moreover, all stages that proceed with the involvement of nucleic acids must occur in the nucleus of the cell. However, this is not the place where protein synthesis occurs. This is the location where preparation for biosynthesis is carried out.
Ribosomal protein biosynthesis
The main place where protein synthesis takes place is the ribosome, a cellular 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 is as follows: the informational RNA formed in the cell nucleus extends 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.
Amino acids are delivered to the place where protein synthesis takes place using transport RNA. One such molecule can once produce one amino acid. They join in turn, depending on the sequence of codons of information RNA. Also, synthesis may stop for a while.
When advancing through mRNA, the ribosome can reach sites (introns) that do not encode amino acids. In these places, the ribosome simply moves along the mRNA, but the attachment of amino acids to the chain does not occur. Once the ribosome reaches the exon, that is, the site that encodes the acid, then it again joins 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 molecule must be organized into a certain structure: secondary, tertiary or even more complex - the quaternary.
Structural organization of protein
The secondary structure is the first stage of structural organization. To achieve this, the primary polypeptide chain must spiral (form alpha-helices) or bend (create beta layers). Then, in order to occupy even less space in length, the molecule is further contracted and wound into a ball due to hydrogen, covalent and ionic bonds, as well as interatomic interactions. Thus, a globular protein structure is obtained .
Quaternary protein structure
The quaternary structure is the most complex of all. It consists of several sites with a globular structure, connected by fibrillar threads of the polypeptide. In addition, the tertiary and quaternary structure may 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. Glycoproteins are also located on cell membranes and act as receptors. However, the molecule is modified not where protein synthesis occurs, but in a smooth endoplasmic reticulum. Here there is the possibility of joining lipids, metals and carbohydrates to the protein domains.