What is a codon?

What is a codon?

• A. A sequence of three bases on an mRNA strand that provides genetic code information for a particular amino acid
• B. A sugar molecule in DNA
• C. A type of enzyme that synthesizes RNA
• D. A nucleotide that pairs with thymine

Answer: (A)

A codon is a set of three nucleotides on messenger RNA that specifies which amino acid will be added next in a growing protein. During translation, the mRNA is read in these three-base units, and each codon directs the correct tRNA carrying its corresponding amino acid to the ribosome. This system uses a nearly universal code: many codons can code for the same amino acid, and some codons signal the termination of protein synthesis, called stop codons. The idea is that the sequence of three RNA bases acts like a code word, telling the cell which amino acid to insert or when to stop. Why the other descriptions don’t fit: a sugar molecule in DNA refers to deoxyribose, not a codon; an enzyme that synthesizes RNA is RNA polymerase, not a codon; a nucleotide that pairs with thymine describes adenine in DNA, which is unrelated to the triplet code that specifies amino acids on mRNA.

A codon is a set of three nucleotides on messenger RNA that specifies which amino acid will be added next in a growing protein. During translation, the mRNA is read in these three-base units, and each codon directs the correct tRNA carrying its corresponding amino acid to the ribosome. This system uses a nearly universal code: many codons can code for the same amino acid, and some codons signal the termination of protein synthesis, called stop codons. The idea is that the sequence of three RNA bases acts like a code word, telling the cell which amino acid to insert or when to stop.

Why the other descriptions don’t fit: a sugar molecule in DNA refers to deoxyribose, not a codon; an enzyme that synthesizes RNA is RNA polymerase, not a codon; a nucleotide that pairs with thymine describes adenine in DNA, which is unrelated to the triplet code that specifies amino acids on mRNA.