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Question #47727
The Question
A human cDNA is cloned into an E. coli expression vector possessing a highly stringent, high-copy-number 'ori' sequence. Post-induction, researchers observe exceptionally high levels of the recombinant mRNA. However, the yield of the functional full-length protein is negligible. Instead, the host cells suffer metabolic exhaustion and accumulate massive amounts of truncated (prematurely terminated) polypeptides. Assuming no mutations occurred during cloning, which of the following is the most scientifically accurate explanation for this observation?
Options
- A.
The high-copy-number 'ori' sequence competitively binds to the host's translational machinery, preventing ribosome assembly on the mRNA.
- B.
The absence of eukaryotic 5' capping and 3' polyadenylation in E. coli causes the recombinant mRNA to degrade rapidly before translation completes.
- C.
The human cDNA utilizes synonymous codons that correspond to rare tRNAs in E. coli, leading to a kinetic bottleneck, ribosomal stalling, and premature termination.
- D.
The bacterial release factors mistakenly recognize eukaryotic sense codons as nonsense codons due to the universality of the genetic code.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
Lac_Operon_Inducibility|Blue-White_Screening|Primary_vs_Secondary_Sewage_Treatment
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize that the genetic code is 'universal' and 'degenerate' (NCERT Molecular Basis of Inheritance) but fail to apply the concept of 'codon bias' in Biotechnology.
A common misconception is that high mRNA transcription (driven by a strong 'ori') guarantees high protein yield, ignoring the translational kinetic bottleneck caused by tRNA scarcity in a heterologous host.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biotechnology : Principles and Processes - Class 12 |
| Concept | Blue-White Screening Mechanism |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |