The introns are _____ out by the _____ leaving only the exons behind.

The introns are _____ out by the _____ leaving only the exons behind.

• A. Retained by ribosome
• B. Spliced by spliceosome
• C. Removed by exonuclease
• D. Edited by polymerase

Answer: (B)

Splicing removes noncoding segments from the initial RNA transcript so only the coding parts remain. The introns are spliced out by the spliceosome, a complex that recognizes the intron–exon boundaries and catalyzes the chemical cuts and joins that connect exons together. This process creates a continuous coding sequence in the mature mRNA. Think of it as the cell using the spliceosome to precisely cut out the introns and glue the exons together, leaving behind a clean message that can be read by the ribosome during translation. The ribosome isn’t involved in removing introns; it reads mRNA later. Exonucleases, which chew nucleotides from ends, wouldn’t specifically remove introns and join exons. Polymerase builds RNA or edits it during synthesis, not the intron removal step here.

Splicing removes noncoding segments from the initial RNA transcript so only the coding parts remain. The introns are spliced out by the spliceosome, a complex that recognizes the intron–exon boundaries and catalyzes the chemical cuts and joins that connect exons together. This process creates a continuous coding sequence in the mature mRNA.

Think of it as the cell using the spliceosome to precisely cut out the introns and glue the exons together, leaving behind a clean message that can be read by the ribosome during translation. The ribosome isn’t involved in removing introns; it reads mRNA later. Exonucleases, which chew nucleotides from ends, wouldn’t specifically remove introns and join exons. Polymerase builds RNA or edits it during synthesis, not the intron removal step here.