Thursday, December 23, 2010
10:22 PM | Posted by Shams Burki | Edit Post
The correct answer is C. This vignette has distractors, so beware. Regardless of how long the untranslated regions are, the number of nucleotides in the coding region of an mRNA is three times the number of amino acids, since three nucleotides are required to code for each amino acid, and 3 X 64 = 192. In reality, three nucleotides code for the first amino acid (formyl-methionine in prokaryotes, methionine in eukaryotes), which may be removed in posttranslational steps, and three nucleotides at the 3'
end (are needed to terminate the process (i.e., a STOP codon), so the actual number would likely be slightly higher.