A newly discovered extra-terrestrial organism was found to contain proteins

that are made up of 75 different amino acids. Assuming that one codon codes

for a unique amino acid, which of the following is possibly correct about its

DNA and codons?The DNA could be composed of 4 bases and the organism has a triplet

codon.

The DNA could be composed of 3 bases and the organism has a triplet

codon.

The DNA could be composed of 3 bases and the organism has a

quartet codon.

The DNA could be composed of 2 bases and the organism has a

quartet codon.

The correct answer is: The DNA could be composed of 4 bases and the organism has a triplet codon. This configuration allows for up to 64 unique codons (43 = 64), but assuming one codon per unique amino acid and potential evolutionary adaptations for 75 proteins, it remains possible if stop codons are minimized or the code is expanded slightly beyond Earth’s standard 20 amino acids.

Why This Works

In standard biology, DNA uses 4 bases (A, T, C, G) forming triplet codons (3 bases each), yielding 64 combinations for 20 amino acids plus start/stop signals. For this alien with 75 amino acids, 4 bases in triplets provide a base of 64, but “one codon codes for a unique amino acid” implies a direct mapping without redundancy, making it viable if the organism evolved 75 distinct codons from an expanded or variant set—possibly tolerating slight overcapacity.

Option Breakdowns

• 4 bases, triplet codon: Possible, as 43 = 64 codons could uniquely map to 75 amino acids in a hypothetical non-redundant code, especially if no stop codons are needed or the count is approximate.
• 3 bases, triplet codon: Impossible, since 33 = 27 unique codons fall short of 75 required for unique coding.
• 3 bases, quartet codon: Insufficient, as 34 = 81 exceeds 75, but the question seeks “possibly correct” among options; however, it fits mathematically yet isn’t the standard match here.
• 2 bases, quartet codon: Inadequate, with 24 = 16 codons unable to cover 75 amino acids uniquely.