A codon is composed of how many nucleotides?

A codon is composed of how many nucleotides?

• A. 1
• B. 2
• C. 3
• D. 4

Answer: (C)

A codon is a group of three nucleotides in mRNA that specifies an amino acid or signals to stop during protein synthesis. That three-nucleotide length is the standard in the genetic code because it provides enough combinations (4 choices per position, so 4^3 = 64 possible codons) to encode all 20 amino acids plus stop signals. Reading mRNA in triplets by the ribosome and matching each codon with a tRNA anticodon brings in the corresponding amino acid to build the protein. For example, AUG codes for methionine and is also the start signal, while UAA, UAG, and UGA are stop codons. Choosing a codon length of one or two nucleotides would provide far too few combinations to encode all amino acids, while four nucleotides would give far more combinations than are needed and isn’t how the code is organized.

A codon is a group of three nucleotides in mRNA that specifies an amino acid or signals to stop during protein synthesis. That three-nucleotide length is the standard in the genetic code because it provides enough combinations (4 choices per position, so 4^3 = 64 possible codons) to encode all 20 amino acids plus stop signals. Reading mRNA in triplets by the ribosome and matching each codon with a tRNA anticodon brings in the corresponding amino acid to build the protein. For example, AUG codes for methionine and is also the start signal, while UAA, UAG, and UGA are stop codons. Choosing a codon length of one or two nucleotides would provide far too few combinations to encode all amino acids, while four nucleotides would give far more combinations than are needed and isn’t how the code is organized.