Final answer:
A series of three nucleotide bases that directs the insertion of a specific amino acid into a polypeptide chain is known as a codon, which is a fundamental unit of the genetic code in mRNA.
Step-by-step explanation:
A series of three nucleotide bases that specifies the insertion of a particular amino acid into a polypeptide chain is a codon. In the genetic code, each amino acid is specified by a set of three consecutive bases of mRNA, known as a codon. This three-nucleotide sequence in mRNA corresponds specifically to one amino acid or a stop signal during the process of protein synthesis. The genetic code is considered to be “degenerate”, meaning that a single amino acid may be encoded by more than one nucleotide triplet. For example, the mRNA codon CAC specifies the amino acid valine. Thus, the sequences of codons in mRNA determine the sequence of amino acids in a protein, essentially directing the assembly of these building blocks into functional proteins.