What alteration does mRNA undergo before leaving the nucleus?

The alteration that mRNA undergoes before leaving the nucleus involves the addition of a 5' cap and a 3' poly-A tail. The 5' cap is a modified guanine nucleotide that is added to the beginning of the mRNA molecule. This structure is crucial as it protects the mRNA from degradation, assists in ribosome binding during translation, and helps with the export of the mRNA from the nucleus to the cytoplasm.

The addition of the 3' poly-A tail, a sequence of adenine nucleotides, also plays a vital role in protecting the mRNA molecule from enzymatic degradation and facilitates the export from the nucleus. Together, these modifications enhance the stability and translation efficiency of mRNA.

This process is part of post-transcriptional modification, which ensures that the mRNA is properly processed before it exits the nucleus for translation into proteins. Other choices do not accurately describe the alterations that occur to mRNA prior to leaving the nucleus. For instance, methylation is a different process that typically refers to the addition of methyl groups to DNA or RNA and is not a fundamental alteration of mRNA leaving the nucleus. Translation into a protein occurs after the mRNA has exited the nucleus, and storage in the nucle