What is a ribosome? Definition:
The ribosomes (Singular: ribosome) are cell organelles that occur in all living organisms, in which, within the framework of protein biosynthesis, the translation, that is, the reading of the mRNA towards the synthesis of proteins, takes place. The term ribosome is derived from the English "ribonucleic acid" (RNA) and the Greek "soma" (body). Due to their important function, the ribosomes are also referred to as "egg producers" of the cells, because in the translation of the mRNA they combine the individual amino acids to amino acid chains and thus ultimately to proteins.
Ribosomes appear under the microscope as oval to round bodies. These tiny particles (between 20-25nm in prokaryotes and 20-30nm in eukaryotes) consist of a complex combination of ribonucleic acid and proteins.
Depending on the cell type and the specific function of the organelle, ribosomes can be classified into four different forms:
Prokaryotes (membrane-bound ribosomes or free ribosomes)
Eukaryotes (membrane-bound ribosomes or free ribosomes)
Structure of the ribosome
The structure of the ribosomes is based on different subunits, within which a large number of proteins are bound. In the case of eukaryotes, the large (60S) and small (40S) subunits are formed separately in the nuclear body (nucleolus) and pass through the nuclear pores into the cytoplasm of the cell. There, the units fuse into the finished ribosomes (80S).
As a basic building block of ribosomes serve special EiweiЯkÃ¶rper and the ribosomal RNA (a specific ribonucleic acid -> rRNA). When protein biosynthesis proceeds, long-chain polypeptides are formed on the ribosome from the individual amino acids. This process takes place in a kind of "tunneling system" on the ribosomal subunit.
Function of the ribosome
The subunits of ribosomes perform different tasks in parallel. The translation of the genetic information from the messenger RNA (mRNA) to amino acids is indispensable. In this context, each single ribosome works as a separate and independent production site for all proteins to be synthesized in the organism. The mode of functioning of the ribosomes can be subdivided into two processes:
1.) The large subunit takes over the linkage of the individual protein building blocks to the long chains, which appear as proteins. This process is called peptidyl transferase activity.
2.) The small subunit is needed for the recognition of the mRNA. Only then can the correct sequence for a combination of amino acids be realized.
The actual information for the sequence of amino acids is contained in the DNA of the chromosomes in the nucleus. For proteins to be synthesized, an exact copy must be made and removed from the cell nucleus, which is taken over by the mRNA. Therefore, the term derives from: mRNA = messenger RNA (messenger RNA).