Present an overview of various forms of posttranscriptional processing in eukaryotes. For each, provide an example.

Question: Provide an overview of various forms of posttranscriptional processing in eukaryotes and their roles in gene expression. Answer: Posttranscriptional processing is a series of modifications that occur after the transcription of a gene into a pre-mRNA molecule in eukaryotic cells. These modifications generate a mature mRNA that is ready for translation and protects the mRNA from degradation. Some common posttranscriptional modifications include: 1. 5' capping - This adds a 7-methylguanosine cap to the 5' end of the mRNA molecule, protecting it from degradation, assisting in nuclear export, and helping recruit translation machinery. 2. 3' polyadenylation - This adds a poly(A) tail to the 3' end of an mRNA molecule, enhancing mRNA stability, nuclear export, and translation efficiency. 3. RNA splicing - This process removes non-coding introns from the mRNA and joins coding exons together to create a continuous reading frame for protein synthesis. 4. Alternative splicing - This allows a single gene to produce multiple mRNA isoforms through combinatorial use of exons, so that distinct protein isoforms can be generated for various cellular processes.