Final answer:
The 5'-end 7methyl-GTP cap and the 3'-end poly(A) tail are post-transcriptional modifications of pre-mRNA, which protect the mRNA from degradation and assist in its translation and export from the nucleus.
Step-by-step explanation:
The 5'-end 7methyl-GTP cap and the 3'-end poly(A) tail are two post-transcriptional modifications of pre-mRNA. These modifications are critical for mRNA stability and function.
5' Capping
As the pre-mRNA is being synthesized, a modification known as the 7-methylguanosine cap is added to the 5' end. This cap protects the mRNA from degradation and is recognized by protein synthesis factors, facilitating the initiation of translation by ribosomes.
3' Poly-A Tail
After transcription is complete, an enzyme known as poly-A polymerase adds a sequence of adenine nucleotides to the 3' end, creating the poly-A tail. This tail not only protects the mRNA from degradation but also is essential for the mRNA's export from the nucleus to the cytoplasm.