Final answer:
Cellular regulation of splicing determines which introns and exons are included in mRNA, often through alternative splicing, which allows a single gene to encode multiple proteins. Splicosomes ensure precise intron removal and exon ligation. Modifications like 5'-end capping, 3'-end poly-A tail addition, and mRNA stability in the cytoplasm also play roles in post-transcriptional regulation.
Step-by-step explanation:
The regulation of which introns and exons are spliced is an essential process for gene expression in eukaryotic cells.
During splicing, introns, the non-coding regions of pre-mRNA, are removed, and the remaining exons, which do code for proteins, are connected or ligated together.
This process is carried out by complexes called spliceosomes which recognize specific sequences at the intron/exon borders.
In alternative splicing, different exons may be included or excluded, resulting in the production of multiple protein variants from a single gene.
This process is tightly regulated and controlled by the cell and can vary depending on the cell type, developmental stage, or other factors.
The frequency of different splicing variants is modulated as a means of gene regulation, contributing to the complexity of protein expression.
Pre-mRNA can also undergo other modifications such as the addition of a GTP cap at the 5'-end and a poly-A tail at the 3'-end.
These modifications are part of the maturation of the mRNA before it exits the nucleus.
Furthermore, the stability and lifespan of the mRNA in the cytoplasm, a factor affecting protein synthesis, can be controlled by elements like microRNAs.