Final answer:
Introns are the non-coding sections of eukaryotic pre-mRNA that are removed during RNA processing, and their correct removal is crucial for synthesizing functional proteins.
Step-by-step explanation:
The portions of eukaryotic mRNA sequence that are removed during RNA processing are called introns. These intervening sequences do not encode functional proteins and are excised from the pre-mRNA through a process known as splicing. Splicing occurs in the nucleus and is essential for producing a functional mRNA molecule that can be translated into protein. Exons, in contrast, are the coding sequences that are expressed and joined together after the removal of introns to form the mature transcript, which then exits the nucleus for translation into protein. It's important that RNA splicing is executed with precision since errors can lead to dysfunctional proteins.