The ribosomes are organelles of the cells . In these structures that lack a membrane, the last steps of the protein synthesis .
The chemical composition of ribosomes is given by protein linked to ribosomal ribonucleic acid (RRNA ) that comes from the nucleolus. Ribosomes may be attached to the endoplasmic reticulum or found in the cytoplasm.
With a size of about 30 nanometers (A nanometer is equivalent to one billionth of a meter, that is to divide one meter into a billion), ribosomes can only be observed with the use of electron microscopes. In the case of eukaryotic cells , the ribosomes are slightly larger (about 32 nanometers) compared to prokaryotic cells (less than 30 nanometers).
In each ribosome it is possible to recognize two subunits: one major and one minor. Both arise from the cell nucleus separately and are linked to each other through charges .
The function of ribosomes is the synthesis of proteins by using the genetic data they receive from Messenger RNA (MRNA ). The mRNA, in short, is ribonucleic acid that houses the genetic code that comes from nucleus of the cell. In this way, it defines how protein amino acids must bind, functioning as a kind of pattern or model for synthesis.
The genetic process that ribosomes develop is known as translation . In it, the ribosome is responsible for "read" the mRNA and then assemble the amino acids provided by the transfer RNA to the protein.
Scientists have distinguished twenty amino acids . Each one is encoded in the genetic code by one or more codons: in total, they are known 64 codons . The codons are nucleotide triplets and the ribosomes, in their translation process, work with these elements.
In addition to the nanometer, this field also uses a unity measure known as svedberg , whose symbol can be so much S as Sv . It is important to note that it is not part of the International System of Units. Its name was conceived in honor of Theodor Svedberg, a chemist and physicist from Sweden, Nobel Prize in Chemistry for having invented the ultracentrifuge (an apparatus of interest for biochemistry, polymer science and molecular biology) and of his contributions to the chemistry of colloids.
The svedberg unit is used to measure the sedimentation coefficient of a macromolecule or a particle when they undergo the centrifugation process under normal conditions; This coefficient is obtained through the division of the constant sedimentation rate of the particle or macromolecule by the acceleration applied to them. It is important to note that S indicates a magnitude of time: 1S is equal to 10 seconds raised to -13 . In addition, it is a unit non additive; this is seen in the case of eukaryotic ribosomes, since, despite containing a subunit of 60S and another of 40S, they give a value end of 80S, instead of 100S.
It is known by the name of mitorribosomes or mitochondrial ribosomes to one of the parts of the apparatus of synthesis protein that mitochondria possess. Its size can range from 50S to 72S, as seen in the genre of protists called Leishmania and in the mushroom genus called Candidarespectively.
Ribosomes seen in plastids (eukaryotic cell organelles found in algae and plants) are called plastidials and resemble those prokaryotes . In the same way as the latter, they measure 70S, although in their major subunit they have a 4S rRNA which, in the prokaryotes, corresponds to that of 5S.