Nucleus – Structure And Function Practice Test

Which RNA processing event occurs in the nucleus but not in the cytoplasm?

Capping Polyadenylation Splicing Export

Correct Answer:

Splicing

Explanation:

Splicing is the RNA processing step that takes place in the nucleus to remove introns from the pre-mRNA, producing a continuous coding sequence. This occurs in the nucleus because the spliceosome machinery, made of small nuclear ribonucleoproteins (snRNPs) and other proteins, operates on the nascent transcript during maturation, before the mRNA is exported to the cytoplasm. In contrast, 5′ capping and 3′ polyadenylation also happen in the nucleus as part of maturation, and export is the transport of the mature mRNA out of the nucleus to the cytoplasm rather than a processing step within the cytoplasm. Therefore, splicing uniquely represents a nucleus-restricted processing event.

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