Final answer:
A sequence of three nucleotide bases that signals the end of a polypeptide chain is known as a stop codon. Stop codons are part of the genetic code that instructs the termination of protein synthesis.
Step-by-step explanation:
A series of three nucleotide bases that signals the end of a polypeptide chain is a stop codon. A codon is a consecutive sequence of three nucleotides on an mRNA molecule that corresponds to a specific amino acid or a signal to terminate protein synthesis.
Of the 64 possible codons in the genetic code, 61 are assigned to amino acids and the remaining three are stop codons, also known as nonsense codons. These codons signal the end of the polypeptide chain, thereby concluding the translation process and releasing the newly synthesized polypeptide from the translation machinery.