What is alternative splicing and how can it affect protein output?

• A. Alternative splicing uses the same exon combination for all transcripts.
• B. Alternative splicing uses different combinations of exons to generate multiple mRNA transcripts, leading to different protein isoforms.
• C. Alternative splicing occurs only in prokaryotes.
• D. Alternative splicing occurs after translation.

Answer: (B)

Alternative splicing allows different combinations of exons to be joined together from the same pre-mRNA, producing multiple mature mRNA transcripts and, consequently, different protein isoforms from a single gene. This process expands protein diversity without needing more genes, because the inclusion or exclusion of specific exons can add or remove protein domains, alter the reading frame, or change signals that affect where the protein goes in the cell or how it interacts with other molecules. Because of these changes, alternative splicing can shift the functional output of a gene—some isoforms may be active in one tissue and not another, or be more or less stable, and in some cases can trigger decay pathways if a premature stop codon is introduced. Splicing occurs in the nucleus during RNA processing and is carried out by the spliceosome with help from regulatory factors; it’s a feature of eukaryotic gene expression, whereas bacteria generally don’t perform this kind of intron splicing.