Q.33 The protein synthesis process in prokaryotes is unique because, in them:
1. Transeription is not followed by Translation
2. Translation is followed by Transcription
3. Transcription is coupled with translation
4. Either transcription or translation – only one process takes place
Prokaryotic Protein Synthesis: Coupled Transcription-Translation Explained
Prokaryotes uniquely couple transcription and translation during protein synthesis due to the absence of a nuclear membrane. The correct answer is option 3: Transcription is coupled with translation, a key concept for exams like CSIR NET and UPSC biotech.
Correct Answer
Option 3: Transcription is coupled with translation.
In prokaryotes, ribosomes bind nascent mRNA as it’s transcribed by RNA polymerase in the cytoplasm, forming RNAP-mRNA-ribosome complexes called expressomes. This coupling ensures efficient gene expression, protects mRNA from degradation, and coordinates elongation rates.
Option Analysis
Option 1: Transcription Not Followed by Translation
Incorrect, as prokaryotes actively perform both processes simultaneously. Uncoupling would disrupt their rapid gene expression; this describes neither prokaryotes nor eukaryotes accurately.
Option 2: Translation Followed by Transcription
Wrong sequence—transcription precedes and overlaps translation. Translation cannot precede transcription since mRNA must be synthesized first.
Option 3: Transcription Coupled with Translation (Correct)
The hallmark of prokaryotic protein synthesis: no nucleus allows immediate ribosome access to emerging mRNA. This speeds response to environmental changes but is absent in eukaryotes.
Option 4: Only One Process Takes Place
False—both occur concurrently and interdependently. Neither is excluded; coupling is essential for prokaryotic efficiency.
| Option | Statement | Correct? | Reason |
|---|---|---|---|
| 1 | No transcription-translation link | No | Both happen together |
| 2 | Translation before transcription | No | Wrong order |
| 3 | Coupled processes | Yes | Cytoplasmic overlap |
| 4 | Only one process | No | Both concurrent |
Exam Relevance
This distinction highlights prokaryotic efficiency vs. eukaryotic spatial separation, crucial for molecular biology questions. NusG protein often mediates coupling.
