Ace A Level Biology 2025 – Dive Deep and Conquer Science!

A codon is defined as a sequence of three bases in DNA or RNA that codes for a specific amino acid. This triplet arrangement of nucleotides is crucial in the genetic code, as it translates the instructions carried by mRNA into a polypeptide chain during the process of protein synthesis. Each codon corresponds to either an amino acid or a stop signal that ends protein synthesis, showcasing the fundamental relationship between nucleic acid sequences and protein formation.

In the context of the other options, a single base pair in DNA does not capture the triplet nature of a codon; proteins are indeed made up of amino acids but are not defined by codons; and while enzymes involved in DNA replication are essential for copying genetic material, they are not related to the definition of a codon itself. This clear role and structure of codons underscore their importance in biological processes, making option B the correct choice.