Based on current knowledge, the gene could be precisely defined as a collection of nucleotides that specify the adjacent amino acid sequences of polypeptide chains of the cell.
It was natural to infer that the corresponding amino acid and nucleotide sequences were to be colinear, and this hypothesis was quickly confirmed by the correlation that existed between the relative locations of the mutations in a gene and the locations of the alterations in its polypeptide product.
It was known as was unthinkable a direct role in establishing the order of amino acids in proteins: in fact, the almost totality 'of the DNA was localized in the chromosomes which are found in the cell nucleus, while protein synthesis was carried out mainly in the cytoplasm.
For this reason, the genetic information of the DNA (the sequence of nucleotides) had to be passed to an intermediate molecule, which would subsequently be transferred into the cytoplasm, where it would then be determined by the order of amino acids.
This "broker" was just the ' RNA.
The passage of genetic information to the structural and functional construction of the cell, therefore, takes place with the following scheme:
This "broker" was just the ' RNA.
The passage of genetic information to the structural and functional construction of the cell, therefore, takes place with the following scheme:
DNA RNA >>>>>>>>>>> >>>>>>>>> PROTEINS
In this regard, there are three types of RNA:
messenger RNA (mRNA), functionally defined as a molecule capable of transferring the genetic information from DNA to the sites where the protein synthesis happens, encoding a specific protein: the various mRNAs present in a cell, in fact, have base sequences complementary to precise segments of DNA (the genes ) able to encode precise proteins;
ribosomal RNA (rRNA), synthesized in the nucleolus associating with proteins forms the ribosomes, which are the seats of protein synthesis of cells;
the transfer RNA (tRNA) that recognizes the codon on the mRNA sequence and binds the corresponding amino acids and transfers them on the ribosome. Per each of the twenty naturally-occurring amino acids, there is at least one specific tRNA can recognize and bind it.
RNA performs additional functions within the cell: in addition to the informational role, this molecule is indeed involved in post-transcriptional regulatory mechanisms that control gene expression at the level of splicing, processing, transport and stability.
The versatility of RNA is further demonstrated by its ability to carry out catalytic functions of splitting and / or formation of phosphodiester bonds.
More recently, then, the discovery that RNA can mediate specific covalent modifications also involved in ribosomal RNA maturation.
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