Question

The number of codons effective in coding twenty amino acids:

• A. 20
• B. 61
• C. 32
• D. 64

Answer 1

Answer: (B)

61

Answer 2

The genetic code is the set of rules by which the nucleotide sequence of DNA or RNA is translated into the amino acid sequence of a protein. Codons, which consist of three nucleotides, are the units that encode specific amino acids or stop signals in the genetic code.
There are 20 standard amino acids commonly found in proteins. However, the total number of possible codons is $64 (4^3)$, which is greater than the number of amino acids. This means that some amino acids are encoded by more than one codon. In fact, 61 out of the 64 codons code for specific amino acids, while the remaining three codons (UAA, UAG, and UGA) serve as stop signals or "termination" codons, indicating the end of protein synthesis.
Therefore, the correct answer is 61, as there are 61 codons that effectively code for the twenty amino acids.