alternative splicing
Summary
Alternative splicing joins the exons of one eukaryotic pre-mRNA in different combinations, producing different mature mRNAs and protein isoforms from a single gene. It is a main reason a cell can make more distinct proteins than it has genes.
Detail
Meaning: Alternative splicing occurs in the nucleus when the spliceosome (snRNPs plus proteins) processes a eukaryotic pre-mRNA. Introns are removed and exons joined, but the exons chosen can vary: some are skipped or swapped. Different cell types or developmental stages use different splicing regulators, so one gene gives several mature mRNAs and protein isoforms. This helps explain why a proteome is larger than the gene count.
On the MCAT: A passage may show a gene with its exons and the mRNAs found in two tissues, then ask which protein forms are possible or why gel bands differ in size. A splice-site mutation can cause exon skipping, giving a shorter or altered protein. Questions also compare genomic DNA, pre-mRNA, and mature mRNA.
Common confusion: Students treat it as a DNA mutation. The gene sequence is unchanged; only the RNA processing differs. It is also distinct from the 5′ cap and poly-A tail, which are added to the transcript but do not change which exons are included. Bacterial genes typically lack introns, so this is mainly a eukaryotic feature.
Sources
- Molecular Biology of the Cell
- Lehninger Principles of Biochemistry
- Molecular Biology of the Gene
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.