If there are 20 amino acids then what is the minimum number of tRNAs that must exist?

If there are 20 amino acids then what is the minimum number of tRNAs that must exist?

• A. 10
• B. 30
• C. 20
• D. 40

Answer: (C)

The key idea is that tRNAs carry specific amino acids. Each amino acid must have at least one tRNA to be properly incorporated by its corresponding aminoacyl-tRNA synthetase. The genetic code is redundant, so many codons code for the same amino acid, and wobble allows a single tRNA to recognize multiple codons. But a tRNA cannot carry more than one amino acid, so wobble cannot reduce the number of distinct tRNA species below the number of amino acids. With 20 standard amino acids, you need at least 20 different tRNAs.

The key idea is that tRNAs carry specific amino acids. Each amino acid must have at least one tRNA to be properly incorporated by its corresponding aminoacyl-tRNA synthetase. The genetic code is redundant, so many codons code for the same amino acid, and wobble allows a single tRNA to recognize multiple codons. But a tRNA cannot carry more than one amino acid, so wobble cannot reduce the number of distinct tRNA species below the number of amino acids. With 20 standard amino acids, you need at least 20 different tRNAs.