What is a codon?

A codon is defined as a three-nucleotide sequence within mRNA that corresponds to a specific amino acid during protein synthesis. This three-nucleotide unit is crucial because it serves as the basic building block for translating genetic information into proteins. Each codon is associated with a specific amino acid or a termination signal, facilitating the assembly of amino acids in the correct order to form a functional protein. The translation process utilizes codons to ensure that the sequence of amino acids matches the sequence originally coded by the DNA.

In contrast, other choices describe different components or functions within the broader context of molecular biology. A sequence of nucleotides that signals the start of transcription refers to promoter regions or specific sequences like the TATA box, but these are not codons. A type of RNA molecule that participates in protein synthesis generally refers to tRNA (transfer RNA) or rRNA (ribosomal RNA), which play vital roles in translating codons but are not themselves codons. Lastly, a unit of genetic material composed of multiple genes describes chromosomal structure or operons, which is different from the function and definition of a codon as a specific three-nucleotide sequence that dictates amino acid composition during protein synthesis.