The present paper is an attempt to outline a possible approach to the study of concrete cellular systems in terms of relational biology as developed by Rashevsky and Rosen. The basic ideas and the formalism of Rosen’s (M,R)-systems, proposed as a model of abstract biological systems, are used in order to represent the cellular protein biosynthesis. A diagram corresponding to the activation of amino acids and synthesis of amino-acyl-transfer RNA, the attachment of t RNA to a specific codon of messenger RNA and peptide bond synthesis with the release of a protein molecule, is constructed. The systemM thus obtained for the synthesis of a proteinp k receives a set of environmental inputs, that is, the twently naturally occurring amino acids and emits a single output, thep k protein. The problem of noncontractibility of inputs in the\(\mathfrak{M}_{p_k }\) system is then analyzed. In our context, it is found that the noncontractibility is not associated with the whole amino acid setS pk but with an “essential amino acid set”\(\bar S_{p_k }\), so that\(\bar S_{p_k } \subseteq S_{p_k }\) and\(S_{p_k } - \bar S_{p_k }\) represent the set of amino acids which can be replaced or absent. According to our considerations, the biochemical concept of “essential amino acid” acquires a new significance, that is, what seems “essential” is linked with the ability to form a giventRNA t ∼a i complex in a suitable augmented dependent set essential for the biosynthesis of a functional protein. Eventually the discussion of re-establishability leads to some important biological implications concerning the existence of ambiguous codons and the degeneracy phenomenon in the genetic code, as anecessary biochemical tool involved in adaptive processes.