Final answer:
The capping of mature mRNA involves the addition of a 7-methylguanosine to its 5' end, which is crucial for mRNA protection and translation initiation.
Step-by-step explanation:
The capping of a mature mRNA is an event that involves the addition of 7-methylguanosine to its 5' end. This modification, also known as the 5' cap, plays several critical roles, including protection of mRNA from degradation and ensuring proper initiation of translation by ribosomes. In essence, a capping enzyme adds a 7-methylguanosine via a 5'-5' phosphate linkage to the 5' end of the growing pre-mRNA. Even as transcription is underway, this process takes place, with the methyl guanosine cap being pivotal for mRNA's successful departure from the nucleus and its association with ribosomes.