In the context of the genetic code, which statement correctly defines a codon in DNA or mRNA?

• A. A sequence of three nucleotides that specifies an amino acid or a stop signal during translation
• B. A sequence of three amino acids that specifies a nucleotide during transcription
• C. A single nucleotide that determines one amino acid in a protein
• D. A noncoding intron segment that is removed during mRNA splicing

Answer: (A)

Verified step by step guidance

1. Understand that a codon is a fundamental concept in molecular genetics related to the genetic code.
2. Recall that the genetic code is read in sets of three nucleotides, which are the building blocks of DNA and RNA.
3. Recognize that each set of three nucleotides, called a codon, corresponds to a specific amino acid or a stop signal during the process of translation.
4. Eliminate incorrect options by noting that codons are not sequences of amino acids, single nucleotides, or noncoding intron segments.
5. Conclude that the correct definition of a codon is: a sequence of three nucleotides that specifies an amino acid or a stop signal during translation.