Question

If instead of 20 amino acids commonly found in proteins, there were 16, what is the minimum size of a codon (using 4 different bases) for encoding amino acids in proteins?

a) 2
b) 3
c) 4
d) 5

Answer 1

The minimum size of a codon for encoding 16 amino acids using 4 different bases would be two. However, a codon must be at least three nucleotides long to include stop signals and account for the degeneracy of the genetic code. Thus, the correct answer is b) 3.

Step-by-step explanation:

If there were only 16 amino acids instead of the commonly found 20 amino acids in proteins, bearing in mind there are 4 different nucleotide bases available, the minimum codon size required to encode these amino acids would be two. This is because with a base-4 system (the four nucleotides being adenine, cytosine, guanine, and uracil in RNA), a codon of two bases can create 42 or 16 different combinations. Thus, each unique pair of nucleotides could theoretically correspond to one amino acid.

The minimum size of a codon needed for this simplified genetic code would still be three nucleotides long to allow for some redundancy or stop codons, which are necessary for signaling the end of protein synthesis. In the actual genetic code, each amino acid is typically encoded by more than one triplet codon, a feature known as degeneracy. This degeneracy helps make cells more robust to mutations, as not all nucleotide changes will alter the encoded amino acid.

Therefore, the minimum size of a codon that could theoretically encode 16 amino acids is two, but for a fully functional genetic code, a codon of at least three is practical and necessary.