What is a codon and what does it code for?

What is a codon and what does it code for?

• A. A three-nucleotide sequence in mRNA that codes for a specific amino acid.
• B. A three-nucleotide sequence in DNA that codes for a stop signal.
• C. A two-nucleotide sequence in mRNA that codes for an amino acid.
• D. A single nucleotide that forms a unit of heredity.

Answer: (A)

A codon is a three-nucleotide sequence in messenger RNA that determines which amino acid will be added next during protein synthesis. This triplet is read by the ribosome during translation, and each codon specifies a particular amino acid (or a signal to stop translation). The genetic code uses these triplets to build proteins; for example, the start codon AUG not only codes for methionine but also marks where translation begins, while certain codons—UAA, UAG, and UGA—signal termination. This idea fits because codons exist in mRNA after transcription, not in DNA itself, and because three nucleotides are needed to specify one amino acid, given there are 64 possible triplets and 20 amino acids. The other options don’t fit: a DNA sequence isn’t the codon used during translation, and a two-nucleotide sequence or a single nucleotide doesn’t encode an amino acid or a hereditary unit, respectively.

A codon is a three-nucleotide sequence in messenger RNA that determines which amino acid will be added next during protein synthesis. This triplet is read by the ribosome during translation, and each codon specifies a particular amino acid (or a signal to stop translation). The genetic code uses these triplets to build proteins; for example, the start codon AUG not only codes for methionine but also marks where translation begins, while certain codons—UAA, UAG, and UGA—signal termination.

This idea fits because codons exist in mRNA after transcription, not in DNA itself, and because three nucleotides are needed to specify one amino acid, given there are 64 possible triplets and 20 amino acids. The other options don’t fit: a DNA sequence isn’t the codon used during translation, and a two-nucleotide sequence or a single nucleotide doesn’t encode an amino acid or a hereditary unit, respectively.