Final answer:
Post-transcriptional regulation includes alternative splicing and polyadenylation of calcitonin and IgM pre-mRNAs. These processes allow a single gene to code for multiple proteins and stabilize mRNA for protein synthesis.
Step-by-step explanation:
During post-transcriptional regulation, calcitonin and IgM pre-mRNAs undergo essential modifications. These include alternative splicing and polyadenylation, crucial steps towards creating mature mRNA molecules ready for protein synthesis.
Alternative splicing is a process where the exons of pre-mRNA produced by RNA polymerase II are rejoined in multiple ways, enabling one gene to code for several proteins. This versatility arises since eukaryotic genes contain exons, which are coding sequences, interspersed by noncoding regions known as introns.
In the cases of calcitonin and IgM pre-mRNAs, splicing is regulated by spliceosomes, which recognize the exon-intron borders, remove the introns, and splice the exons together to form various mRNA isoforms. Exons can be reconnected in different sequences, which results in different proteins being synthesized from the same gene.
Polyadenylation involves the addition of a 'poly-A tail' at the 3'-end of the mRNA molecule, which stabilizes the mRNA and regulates its nuclear export and lifespan in the cytoplasm. Both splicing and polyadenylation are essential for producing mature mRNA that can be translated into proteins.