Which of the following is true for RNA processing ?

Options

A. Exons are excised before the m-RNA processing
B. Assemblies of protein and snRNPs, called spliceosomes, may catalyze splicing
C. The RNA transcript that leaves the nucleus may be much longer than the original transcript
D. Large quantities of r-RNA are assembled into ribosomes

Answer

To determine which statement is true regarding RNA processing, let's analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding RNA Processing**:
- RNA processing occurs in eukaryotic cells where the initial RNA transcript (pre-mRNA) undergoes modifications before it can be translated into a protein.

2. **Option Analysis**:
- **Option 1**: "Introns are excised before the mRNA processing."
- This statement is incorrect. In fact, introns (non-coding regions) are excised during RNA processing, which is a part of the overall mRNA processing.

- **Option 2**: "The assembly of proteins and snRNPs called spliceosomes may catalyze the splicing."
- This statement is correct. Spliceosomes, which are complexes made of small nuclear RNAs (snRNAs) and proteins (snRNPs), are responsible for the splicing process where introns are removed and exons are joined together.

- **Option 3**: "The RNA transcript that leaves the nucleus may be much longer than the original transcript."
- This statement is incorrect. The RNA transcript that leaves the nucleus (mature mRNA) is actually shorter than the original transcript (pre-mRNA) because introns are removed during processing.

- **Option 4**: "Large quantities of rRNA are assembled into the ribosome."
- This statement is misleading. While rRNA is indeed a component of ribosomes, the assembly of ribosomal RNA occurs in the nucleolus, not in the ribosome itself.

3. **Conclusion**:
- The only true statement regarding RNA processing is **Option 2**: "The assembly of proteins and snRNPs called spliceosomes may catalyze the splicing."

### Final Answer:
The correct answer is **Option 2**.

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