What is alternative splicing and how does it increase protein diversity?

• A. The splicing of pre-mRNA by the spliceosome removes introns but never affects exon composition.
• B. The process adds poly-A tails to mRNA after transcription.
• C. The splicing of pre-mRNA by the spliceosome can include or exclude exons to generate multiple mature mRNA isoforms.
• D. Splicing creates multiple promoters for different transcripts.

Answer: (C)

Alternative splicing is the process by which the spliceosome can include or exclude certain exons during pre-mRNA processing, producing multiple mature mRNA isoforms from a single gene. By choosing different splice sites, a gene can generate protein variants with different combinations of exons, which often alters the presence or absence of functional domains, affecting the protein’s activity, localization, and interactions. This ability to mix and match exons across transcripts markedly increases the diversity of proteins a single gene can yield, and it is often regulated in a tissue-specific or developmental stage-specific manner. For example, some exons might be included in one tissue to confer a particular function, while the same gene omits that exon in another tissue, leading to a different protein. In contrast, polyadenylation adds a poly-A tail after transcription (not part of splicing), and promoters are DNA elements that control where transcription begins rather than how exons are joined, so those statements describe different processes.