Q.92 Which ONE of the following processes does NOT occur in prokaryotic gene expression, but occurs
in eukaryotic gene expression?
(A) Transcription of mRNA, tRNA, and rRNA
(B) Binding of RNA polymerase to the promoter
(C) Addition of a poly-A tail to the 3′ end and the 5′ capping of an mRNA
(D) Translation begins as soon as transcription is initiated
Gene expression differs markedly between prokaryotes and eukaryotes due to cellular complexity, with eukaryotes featuring mRNA processing absent in prokaryotes. This MCQ highlights a key distinction vital for genetics and biotechnology students revising transcription-translation pathways.
**Correct Answer: (C) Addition of a poly-A tail to the 3′ end and the 5′ capping of an mRNA **
Eukaryotic mRNA undergoes post-transcriptional modifications like 5′ capping (7-methylguanosine addition) and 3′ poly-A tailing for stability, export, and translation efficiency—processes unnecessary in prokaryotes lacking nucleus and introns.
Core Differences in Gene Expression
Prokaryotes couple transcription and translation in the cytoplasm, with minimal RNA processing. Eukaryotes separate these in nucleus and cytoplasm, requiring mRNA maturation: capping, polyadenylation, and splicing.
Explanation of All Options
Each option tests familiarity with shared vs unique steps:
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(A) Transcription of mRNA, tRNA, and rRNA: Occurs in both. Prokaryotes and eukaryotes transcribe all RNA types using RNA polymerases.
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(B) Binding of RNA polymerase to the promoter: Common to both. Prokaryotes use sigma factors; eukaryotes use TBP/TATA box equivalents for initiation.
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(C) Addition of a poly-A tail to the 3′ end and the 5′ capping of an mRNA: Eukaryote-exclusive. Prokaryotic mRNA is translated directly without caps or tails, as it’s short-lived and polycistronic.
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(D) Translation begins as soon as transcription is initiated: Prokaryote hallmark (coupled processes). Eukaryotes prevent this via nuclear membrane until processing completes.
| Option | Occurs in Prokaryotes? | Occurs in Eukaryotes? | Key Difference |
|---|---|---|---|
| (A) RNA transcription | Yes | Yes | Shared process |
| (B) Pol-promoter binding | Yes | Yes | Shared initiation |
| (C) Poly-A tail & 5′ cap | No | Yes | Eukaryote-only |
| (D) Coupled translation | Yes | No | Prokaryote-specific |
Exam Tips for Biology Students
Links to prior topics like TATA box (eukaryotic promoter) and glycolysis (energy for expression). In bioinformatics, align sequences to spot poly-A signals. Master for NEET or molecular biology exams focusing on RNA processing.
