The "universal" genetic code is now known to have exceptions. Evidence for this can be found if which of the following is TRUE?
A) if UGA, usually a stop codon, is found to code for an amino acid such as tryptophan (usually coded for by UGG only) in a different organism
B) if one stop codon, such as UGA, is found to have a different effect on translation than another stop codon, such as UAA
C) if prokaryotic organisms are able to translate a eukaryotic mRNA and produce the same polypeptide
D) if several codons are found to translate to the same amino acid, such as serine
E) if a single mRNA molecule is found to translate to more than one polypeptide when there are two or more AUG sites

Question

Quizplus · Accepted Answer

The fact that UGA, normally a stop codon, codes for an amino acid like tryptophan in certain organisms demonstrates that the genetic code is not entirely universal.

Answer: B
 If different stop codons have varying effects on translation, this indicates that the genetic code is not completely universal.

Answer: E
 If a single mRNA molecule can translate to multiple polypeptides, it implies that there may be multiple reading frames or alternative codon usage, which suggests that the genetic code may not always be universal.

Option C is incorrect because prokaryotes and eukaryotes use the same genetic code, and therefore, their translation mechanisms would not reveal any exceptions. Option D is incorrect because redundant codons coding for the same amino acid are still following the same genetic code.

The "Universal" Genetic Code Is Now Known to Have Exceptions