Which of the following comparisons of prokaryotic transcription and eukaryotic transcription is incorrect ?

Options

A. Prokaryotic transcription-Transcriptional unit has only one gene
Eukaryotic transcription-Transcriptional unit has one or more genes
B. `{:("Prokaryotic transcription Eukaryotic transcription"),("Occurs in the cytoplasm
Occurs in the nucleus"):}`
C. `{:("Prokaryotic transcription Eukaryotic transcription"),("A single RNA polymerase synthesises all the three types of RNA The RNA polymerase I,II, and III synthesise rRNA,mRNA and tRNA res"):}`
D. `{:(" Prokaryotic transcription Eukaryotic transcription"),("Coupled-transcription translation is the rule Coupled-transcription-translation is not possible"):}`

Answer

To determine which comparison of prokaryotic transcription and eukaryotic transcription is incorrect, we can analyze the provided statements step by step.

### Step 1: Understand Prokaryotic Transcription
- In prokaryotes, transcription occurs in the cytoplasm and is coupled with translation. This means that as soon as mRNA is synthesized, ribosomes can begin translating it into proteins without the need for processing.
- Prokaryotic transcription typically involves a single RNA polymerase that synthesizes all types of RNA (mRNA, tRNA, and rRNA).

### Step 2: Understand Eukaryotic Transcription
- In eukaryotes, transcription occurs in the nucleus, and the mRNA must undergo processing (capping, polyadenylation, and splicing) before it can be translated in the cytoplasm.
- Eukaryotic cells have three different RNA polymerases (RNA polymerase I, II, and III) that synthesize different types of RNA:
- RNA polymerase I synthesizes rRNA (except for 5S rRNA).
- RNA polymerase II synthesizes mRNA.
- RNA polymerase III synthesizes tRNA and 5S rRNA.

### Step 3: Analyze the Statements
1. **Statement A**: "Transcriptional unit has only one gene."
- This is incorrect for prokaryotes, as they can have operons where multiple genes are transcribed together.

2. **Statement B**: "Occurs in cytoplasm (prokaryotes) and occurs in the nucleus (eukaryotes)."
- This statement is correct.

3. **Statement C**: "A single RNA polymerase synthesizes all three types of RNA."
- This statement is correct for prokaryotes but incorrect for eukaryotes, where three different RNA polymerases are involved.

4. **Statement D**: "Coupled transcription and translation."
- This statement is correct for prokaryotes, as transcription and translation occur simultaneously.

### Conclusion
The incorrect comparison is **Statement A**, as it misrepresents the nature of transcriptional units in prokaryotes.

### Final Answer
The incorrect comparison of prokaryotic transcription and eukaryotic transcription is **Statement A**: "Transcriptional unit has only one gene."

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