Which complex catalyzes the removal of introns from pre-mRNA?

Which complex catalyzes the removal of introns from pre-mRNA?

• A. The spliceosome catalyzes intron removal
• B. The ribosome translates mRNA
• C. The exosome degrades RNA
• D. The proteasome splices proteins

Answer: (A)

Intron removal from pre-mRNA is carried out by the spliceosome, a large RNA–protein complex that coordinates splicing in the nucleus. It uses small nuclear RNAs (snRNAs) and many proteins to recognize the 5' splice site, the branch point, and the 3' splice site. Through two transesterification reactions, the spliceosome cuts at the 5' splice site and forms a lariat with the branch point, then joins the neighboring exons and releases the intron as a lariat. This processing converts pre-mRNA into mature mRNA ready for export and translation. Ribosomes are responsible for translating mature mRNA into proteins, not removing introns. The exosome degrades RNA molecules, helping with RNA turnover rather than splicing. The proteasome targets proteins for degradation rather than removing introns or splicing RNA.

Intron removal from pre-mRNA is carried out by the spliceosome, a large RNA–protein complex that coordinates splicing in the nucleus. It uses small nuclear RNAs (snRNAs) and many proteins to recognize the 5' splice site, the branch point, and the 3' splice site. Through two transesterification reactions, the spliceosome cuts at the 5' splice site and forms a lariat with the branch point, then joins the neighboring exons and releases the intron as a lariat. This processing converts pre-mRNA into mature mRNA ready for export and translation.

Ribosomes are responsible for translating mature mRNA into proteins, not removing introns. The exosome degrades RNA molecules, helping with RNA turnover rather than splicing. The proteasome targets proteins for degradation rather than removing introns or splicing RNA.