_______do not appear in mature of processed RNA.

Answer

**Step-by-Step Solution:**

1. **Understanding mRNA**: Begin by recognizing that mRNA (messenger RNA) is a type of RNA that carries genetic information from DNA to the ribosome, where proteins are synthesized. In eukaryotes, mRNA is initially synthesized as a precursor molecule known as pre-mRNA.

2. **Pre-mRNA Composition**: Pre-mRNA contains both coding sequences (exons) and non-coding sequences (introns). Exons are the parts of the gene that will be expressed (translated into protein), while introns are segments that do not code for proteins.

3. **Processing of mRNA**: The pre-mRNA undergoes a processing stage where introns are removed, and exons are spliced together. This process is essential for the formation of mature mRNA.

4. **Mature mRNA Composition**: After processing, the mature mRNA consists only of exons, which are the coding sequences that will be translated into proteins. The introns, being non-coding sequences, are eliminated during this processing.

5. **Conclusion**: Therefore, the components that do not appear in mature or processed mRNA are the introns.

**Final Answer**: Introns do not appear in mature processed RNA.

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