Question

Introns are known to contain termination codons (UAA, UGA, or UAG) yet these codons do not interrupt the coding of a particular protein. Why?

a. UAA, UGA, and UAG are initiator codons, not termination codons
b. Exons are spliced out of mRNA before translation
c. These triplets cause frameshift mutations, but not termination
d. More than one termination codon is needed to stop translation
e. Introns are removed from mRNA before translation

Answer 1

Introns, which may contain termination codons, are removed from mRNA before translation, hence the stop codons within introns do not affect protein synthesis.

Step-by-step explanation:

While introns may contain termination codons (UAA, UGA, or UAG), these codons do not interrupt the coding of a particular protein because introns are removed from mRNA before translation. The process of removing introns and splicing together the remaining exons, which do code for proteins, is called splicing. The spliced mRNA, now devoid of introns, is then exported from the nucleus to the cytoplasm for translation. Translation commences with the start codon AUG, and continues until a stop codon (UAA, UGA, or UAG) is encountered on the processed mRNA, which signals the termination of protein synthesis.