Final answer:
The failure to cap an RNA polymerase II transcript in eukaryotic cells disrupts splicing, stability, and translation, rendering it incompatible with life. The 5'-cap and poly-A tail crucially influence mRNA function and stability, which are fundamental to gene expression and protein synthesis.
Step-by-step explanation:
The statement regarding the necessity of capping RNA polymerase II transcripts in eukaryotic cells for proper splicing, stability, and translation is true. The addition of a 5'-cap to the mRNA transcript is a critical modification that affects several aspects of mRNA function. Without this cap, initiation factors cannot properly bind to mRNA, which hampers the initiation of translation as well as the correct splicing and stability of the transcript. Furthermore, capping ensures that the mRNA is recognized by the necessary cellular machinery to prevent degradation and support exporting from the nucleus to the cytoplasm for translation. This cap also plays a role in promoting the removal of introns by spliceosomes in a process known as RNA splicing. Failure to cap an mRNA transcript would ultimately result in a nonfunctional RNA molecule, which cannot be translated into protein. The polyadenylation at the 3' end of mRNA, termed the poly-A tail, is also crucial for RNA stability and is catalyzed by the enzyme polyadenylate polymerase. Together, these modifications make eukaryotic mRNA much more stable than its prokaryotic counterparts, allowing for an extended lifespan and a greater opportunity for protein synthesis.