Final answer:
Eukaryotic genes include noncoding sequences known as introns which are removed from pre-mRNA during RNA splicing. Introns are vital for correct gene expression, and the noncoding DNA contributes to several regulatory and structural functions within the cell.
Step-by-step explanation:
Eukaryotic genes are composed of exons and intervening sequences called introns. Introns are removed from the pre-mRNA during processing. These non-coding sequences do not encode functional proteins, and their presence is necessary to ensure that the coding exons join together correctly to produce a functional polypeptide. Any errors in the RNA splicing process, even a single nucleotide, can result in a nonfunctional protein. The splicing out of introns and rejoining of exons is facilitated by a spliceosome, which ensures the correct sequence of the mature mRNA.
In addition to their role in precursor mRNA processing, noncoding DNA, including introns, may contribute to gene regulation, DNA packaging, chromosomal stability, and the formation of small noncoding RNA molecules. While once considered "junk DNA", many noncoding regions are now recognized as having essential functions within the cell.