Transcription
Most genes code for the synthesis of polypeptide chains. But how does the translation of a code made of nucleotides, like that of DNA, into an alphabet made up of very different letters occur?
The amino acids of proteins are the fundamental unit of the genetic code and the codon. A triplet of nitrogenous bases, each codon guides the synthesis of a particular amino acid. The expression of the genetic code involves different cellular structures and requires different phases for its implementation.
First of all, the DNA guides the synthesis of a complementary RNA molecule, the messenger RNA, through the process of transcription. Messenger RNA then migrates from the nucleus towards the ribosomes, the molecular machines responsible for protein synthesis, that is, the translation of messenger RNA into polypeptide chains.
Translation is based on the correspondence between triplets of nitrogenous bases and amino acids. However, the types of nitrogenous bases that constitute the genetic code are four nucleic acids. Therefore, there are 64 combinations of different triplets against a total of just twenty amino acids that make up proteins.
This means that more triplets code for the same amino acid, and for this reason, it is said that the genetic code is redundant or degenerate. However, some codons do not lead to the synthesis of any amino acid and are called nonsense codons or stop codons because they indicate the point at which to end the synthesis of the polypeptide chain.
The genetic code and the universal alphabet of the biological world is common to all forms of life, preserved over time by evolution for its unparalleled effectiveness.