Four bases in RNA carry instructions for 20 amino acids through the process of codon recognition. Codons are sequences of three RNA bases that correspond to specific amino acids. Each codon either codes for a particular amino acid, or it signals the start or stop of protein synthesis. There are 64 possible codons; of these, 61 code for amino acids, while the remaining three are stop codons.

The recognition of codons is performed by structures called ribosomes. Ribosomes are large molecular machines made up of RNA and protein components. They are found in all living cells and serve as the site of protein synthesis.

During protein synthesis, the ribosome reads the sequence of codons in the RNA molecule and uses this information to determine which amino acids should be added to the growing protein chain. Each codon is recognised by a specific transfer RNA (tRNA) molecule that carries the corresponding amino acid. The tRNA molecule binds to the ribosome and delivers its amino acid to the growing protein chain.

By combining different codons in various sequences, the four bases in RNA can provide the instructions for building proteins with 20 different amino acids. This allows for the synthesis of a wide variety of proteins that are essential for cell structure and function.