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Question #45883
The Question
A researcher introduces a nematode-specific transcription unit into a host plant via an Agrobacterium vector. The transcription unit possesses a highly active promoter and a precise terminator. While nuclear assays confirm that the structural gene is accurately transcribed exactly within its physical boundaries, the corresponding functional protein is entirely absent in the cytoplasm. Which of the following statements correctly identifies the mechanism responsible for this phenomenon?
Options
- A.
The primary transcript undergoes alternative splicing in the cytoplasm, rendering the resulting mRNA translationally inert.
- B.
The transcription unit produces both sense and antisense RNAs that hybridize to form dsRNA, triggering post-transcriptional mRNA cleavage by the RISC complex.
- C.
The host plant's RNA polymerase III fails to recognize the foreign terminator, leading to the degradation of an abnormally long transcript.
- D.
The promoter undergoes heavy DNA methylation post-transcriptionally, which prevents the ribosomal subunits from binding to the mRNA in the cytoplasm.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
Promoter|Terminator|siRNA|RISC
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Differentiating between transcriptional silencing (nuclear) and post-transcriptional silencing (cytoplasmic).
Students often assume that if a promoter and terminator function correctly, protein expression is guaranteed.
The trap tests the understanding that RNAi acts as a 'boundary override'—even if the transcription unit is perfectly transcribed in the nucleus, the resulting mRNA is sequestered and degraded by the RISC complex in the cytoplasm before translation can occur.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Molecular Basis of Inheritance - Class 12 |
| Concept | Transcriptional Unit Boundaries |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |