Eukaryotic mRNA processing — The mature mRNA from which source would be expected to carry a 3′ poly(A) tail?
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AA restriction endonuclease gene expressed in Escherichia coli
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BBacterial alpha-amylase mRNA from Bacillus species
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CHuman insulin mRNA transcribed in pancreatic beta cells
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DBacteriophage DNA ligase mRNA in an infected E. coli
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EArchaeal ribosomal protein mRNA
Answer
Correct Answer: Human insulin mRNA transcribed in pancreatic beta cells
Explanation
Introduction:Polyadenylation is a hallmark of most eukaryotic mRNAs, enhancing stability, nuclear export, and translation. This question distinguishes eukaryotic mRNA processing from bacterial and phage transcripts.
Given Data / Assumptions:
- Eukaryotic pre-mRNAs are typically 5′-capped, spliced, and 3′-polyadenylated.
- Bacterial and bacteriophage mRNAs usually lack long 3′ poly(A) tails that function like eukaryotic poly(A); short polyadenylation in bacteria often marks decay.
- Human insulin is a eukaryotic gene expressed in human cells.
Concept / Approach:Identify the organismal origin of the mRNA. Eukaryotic mRNAs (e.g., human insulin mRNA) receive a poly(A) tail via poly(A) polymerase after cleavage at a consensus site; bacterial/phage transcripts generally do not have this eukaryotic-style modification.
Step-by-Step Solution:
1) Determine source: human vs bacterial/phage.2) Apply processing rule: eukaryotes → poly(A); bacteria/phage → typically no such tail for stability/translation.3) Conclude human insulin mRNA has a poly(A) tail.Verification / Alternative check:mRNA isolation protocols (oligo-dT selection) enrich eukaryotic polyadenylated transcripts such as insulin mRNA, confirming the presence of a poly(A) tail.
Why Other Options Are Wrong:
a,b,d) Prokaryotic/phage mRNAs lack canonical eukaryotic polyadenylation; any bacterial poly(A) often promotes decay.e) Many archaeal transcripts are not polyadenylated like eukaryotic mRNAs.Common Pitfalls:Assuming all RNAs have poly(A); conflating bacterial polyadenylation (RNA turnover) with eukaryotic stabilization.
Final Answer:Human insulin mRNA.