Apentix/AP Biology/Unit 6: Gene Expression and Regulation/Question
AP Biologyhardmcq1 pt

Researchers try to express a human gene that contains several introns in E. coli. Production from the cloned genomic sequence fails, but production from a cDNA copy succeeds. Why does the cDNA version work?

A.cDNA was reverse transcribed from mature mRNA, so it lacks the introns that bacteria cannot remove from transcripts
B.cDNA carries stronger bacterial promoters inherited from the cloning reaction
C.Genomic DNA cannot enter bacterial cells, whereas cDNA passes through easily
D.cDNA replicates independently in the cytoplasm without the bacterial chromosome

Explanation

Core Concept

The human genomic sequence retains introns between its coding segments. Bacterial cells have no spliceosome, so introns in the transcript would remain unremoved and wreck the reading frame, yielding useless protein. A cDNA copy is synthesized in vitro from fully spliced mature mRNA, giving one continuous coding sequence. Bacterial machinery then transcribes and translates it correctly.

Correct Answer

AcDNA was reverse transcribed from mature mRNA, so it lacks the introns that bacteria cannot remove from transcripts

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