MCAT Biochemistry Question 101: Answer and Explanation
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Question: 101
11. A gene encodes a protein with 150 amino acids. There is one intron of 1000 base pairs (bp), a 5′-untranslated region of 100 bp, and a 3′-untranslated region of 200 bp. In the final mRNA, about how many bases lie between the start AUG codon and final termination codon?
- A. 150
- B. 450
- C. 650
- D. 1750
Correct Answer: B
Explanation:
The untranslated regions of the mRNA will not be turned into amino acids. Translation will begin with codon 1 (which would be AUG). Because there are 150 amino acids, we can surmise that there will be 151 codons. Each codon will use 3 nucleotides, so 150 × 3 = 450 because codon 151 will be the stop codon.