asmi
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A gene encodes a protein with 150 aminoacids.There is one intron of 1000 bps , a 5' UTR of 100 bps and a 3' UTR of 200 bps .In the final processed mRNA, how many bases lie between the start AUG codon and the final termination codon ?
A. 1750
b.750
c.650
d.450
e150
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| usmleasr
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750 8)
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| black_tulip
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450bp
no intron in the mature mRNA.
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| asmi
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can you explain it further black tulip...
The answer given says 3 x 150 = 450
I didn't get it :roll:
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| Sakaki-
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Between the start codon and the termination codon lie 450 bp since each amino acid corresponds to one codon (3 amino acids) on the mRNA. The UTRs don't matter since it asks for the number of base pairs between the start codon and the termination codon.
150 aa*3 bp/aa (on processed mRNA) = 450 bp
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| black_tulip
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The gene sequence in genomic DNA usually contains 5' UTR, ORF region and 3' UTR. (UTR=untranslated region, ORF=open reading frame) 5' and 3' UTR are important for the regulation of mRNA translation, but not part of ORF. ORF is the right sequence for protein translation, so its sequence must contain 3x base pairs.
introns can be anywhere in the gene. For a hnRNA of this gene in this question, it contains the 1000bp intron which can be anywhere, we don't know long from the start codon to the stop codon, but the full-length of this hnRNA is totally 1000+100+450+200=1750bp. After edition, the 1000 bp intron is removed, so the full-length is 750.
So remember, for a mature mRNA, the ORF region (from start codon to stop codon) is always equal to 3 times of amino acid number. and it has nothing to do with 5' or 3' UTR or introns.
But, actully the 3' UTR for the mature mRNA of a gene is variable since the poly A tail is variable (maybe up to 200 As).
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| asmi
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thanks a lot blacktulip .
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