What are introns?

Introns are defined as non-coding nucleotide sequences within a gene that are transcribed into pre-mRNA but are removed during the RNA splicing process before the mRNA is translated into proteins. The splicing process involves cutting out these introns and joining together the remaining sequences, known as exons, to form a mature mRNA molecule that can be translated into protein.

Understanding the role of introns highlights their importance in gene expression and regulation. Even though introns do not encode for proteins, they can play various roles in the regulation of gene expression and alternative splicing, which allows a single gene to produce multiple protein isoforms. This adds complexity to gene regulation and can result in diverse functional outcomes from a single genetic sequence.

The other options describe different aspects of genetic information or cellular function but do not accurately characterize introns. For instance, while nucleotide sequences that code for proteins are known as exons, introns do not fulfill this role. Functional components of ribosomes pertain to the mechanisms of protein synthesis rather than the structural features of genes. Lastly, segments that are retained in mature mRNA specifically refer to exons, further distinguishing them from introns.