Which molecular complex removes introns from pre-mRNA?

Which molecular complex removes introns from pre-mRNA?

• A. Ribosome
• B. Spliceosome
• C. RNA polymerase
• D. Ligase

Answer: (B)

In eukaryotic gene expression, intron removal is done by the spliceosome, a large ribonucleoprotein complex. It recognizes the 5' and 3' splice sites and the branch point on pre-mRNA and assembles from snRNPs (U1, U2, U4, U5, U6) to form the active catalytic machine. Through two transesterification steps, the spliceosome first cuts at the 5' splice site and forms a lariat intermediate at the branch point, then ligates the adjacent exons together, releasing the intron as a lariat. Translation machinery like the ribosome and transcription machinery like RNA polymerase are responsible for later stages of gene expression, not intron removal. Ligases are involved in joining nucleic acids in various contexts, but the specific complex that removes introns from pre-mRNA is the spliceosome.

In eukaryotic gene expression, intron removal is done by the spliceosome, a large ribonucleoprotein complex. It recognizes the 5' and 3' splice sites and the branch point on pre-mRNA and assembles from snRNPs (U1, U2, U4, U5, U6) to form the active catalytic machine. Through two transesterification steps, the spliceosome first cuts at the 5' splice site and forms a lariat intermediate at the branch point, then ligates the adjacent exons together, releasing the intron as a lariat. Translation machinery like the ribosome and transcription machinery like RNA polymerase are responsible for later stages of gene expression, not intron removal. Ligases are involved in joining nucleic acids in various contexts, but the specific complex that removes introns from pre-mRNA is the spliceosome.