What is the purpose of a 5' cap on mRNA?

The 5' cap on mRNA serves several crucial functions, which is why it is the correct choice. One of its primary roles is to protect the mRNA molecule from degradation by exonucleases, which can rapidly degrade uncapped RNA. The 5' cap is a modified guanine nucleotide that is added to the 5' end of the mRNA molecule shortly after transcription begins. This cap structure not only stabilizes the mRNA but also prevents it from being recognized and degraded by cellular enzymes.

Additionally, the 5' cap aids in the binding of the ribosome during the process of translation. Ribosomes recognize the cap structure, which is essential for the initiation of translation. This binding is crucial since it helps initiate the correct positioning of the ribosome at the start codon of the mRNA, ensuring efficient and accurate protein synthesis.

By contributing to mRNA stability and facilitating ribosome binding, the 5' cap plays a foundational role in the overall process of gene expression, making it a key feature of eukaryotic mRNA processing. Other options, while important aspects of RNA biology, do not accurately reflect the primary purposes of the 5' cap, which is fundamentally about protecting the mRNA and promoting its translation