What is the purpose of 5' capping, 3' polyadenylation, and intron/exon splicing in eukaryotic transcription?

• A. To terminate transcription
• B. To process the primary transcript into mature mRNA for export and translation
• C. To replicate DNA
• D. To degrade RNA

Answer: (B)

These modifications convert a newly made RNA transcript into a mature messenger RNA that can exit the nucleus and be used to make protein. The 5' cap is added early and consists of a modified guanine nucleotide that protects the RNA, helps it be recognized by the ribosome, and assists in exporting the message from the nucleus. The 3' polyadenylation adds a poly-A tail after the RNA is cleaved, which further stabilizes the molecule, aids in nuclear export, and enhances translation efficiency. Splicing removes noncoding introns and joins coding exons, creating a continuous coding sequence and allowing different combinations of exons (alternative splicing) to produce diverse proteins. Together, these processing steps ensure the transcript is stable, properly exported, and ready for translation. They are not about terminating transcription, replicating DNA, or degrading RNA, which are separate processes.