Final answer:
A series of triplet nucleotide bases within a gene specifies each amino acid in a protein, as defined by the genetic code which consists of three-nucleotide codons.
Step-by-step explanation:
Within a gene, it is a series of triplet nucleotide bases that specify each amino acid that will be built into a protein. Proteins are composed of chains of amino acids, and the genetic code is what determines the sequence of amino acids. The genetic code is made up of codons, which are groups of three nucleotides (A, T, C, G in DNA or A, C, G, U in RNA) that correspond to specific amino acids.
Each grouping of three bases in DNA, known as a codon, is transcribed into messenger RNA (mRNA) and then translated into an amino acid during protein synthesis. The sequence of amino acids in a protein determines its structure and function, and this sequence is directed by the sequence of codons in the mRNA which were originally encoded in the DNA.