Final answer:
The three major modifications in mRNA processing in eukaryotes are 5' capping, splicing, and 3' polyadenylation. These modifications are crucial for mRNA stability, export from the nucleus, and the accurate translation of the genetic code into protein.
Step-by-step explanation:
The three major modifications in mRNA processing in eukaryotes are: 5' capping, 3' polyadenylation, and splicing. After transcription, the eukaryotic pre-mRNA is first capped at the 5' end, which involves the addition of a 5' methylguanosine cap.
This cap is essential for mRNA stability and is involved in the initiation of translation. Subsequently, the pre-mRNA undergoes splicing, where introns (non-coding regions) are removed and exons (coding regions) are joined together to form a contiguous coding sequence.
Lastly, 3' polyadenylation adds a series of adenine nucleotides to the 3' end of the mRNA, further stabilizing the molecule and regulating its export from the nucleus to the cytoplasm. These processing steps are critical for the creation of a stable and functional mRNA molecule that is ready for translation into protein.