Final answer:
Introns are removed from eukaryotic pre-mRNA through splicing while still in the nucleus, conducted by spliceosomes to accurately join exons together before mRNA is translated.
Step-by-step explanation:
In eukaryotic cells, the preliminary RNA transcript, known as pre-mRNA, contains both protein-coding sequences (exons) and non-coding sequences (introns). The introns are removed in a process called splicing, which occurs while the pre-mRNA molecule is still within the nucleus. This precise process is crucial for proper gene expression because if it errs by even a single nucleotide, it could result in a dysfunctional protein. Spliceosomes, which are complexes of proteins and RNA molecules, conduct this splicing process, removing introns with high accuracy and precision. Once all introns are removed and exons are accurately rejoined, the mature mRNA is then transported out of the nucleus to the cytoplasm for translation. This quality control ensures that the final mRNA reflects the correct protein-coding information from the exons.