Final answer:
In the cytoplasm of eukaryotes, the final mRNA is a processed transcript that has a 5' cap, a poly-A tail, and has undergone splicing to remove introns. These modifications protect it from degradation and enable the mRNA to be used for protein synthesis over several hours.
Step-by-step explanation:
The final mRNA as it exists in the cytoplasm of a eukaryote is a mature transcript that has undergone several crucial modifications. Initially, during transcription, the eukaryotic pre-mRNA receives a 5' methylguanosine cap and a poly-A tail at the 3' end, both of which serve to protect the mRNA from degradation. Following this, splicing takes place where introns (non-coding regions) are cut out, and exons (coding regions) are joined together to form a continuous coding sequence. Only those mRNAs that have been capped, polyadenylated, and spliced are transported from the nucleus to the cytoplasm.
Upon reaching the cytoplasm, the mRNA associates with ribosomes to begin protein synthesis, whereby the information encoded in the mRNA is used to build a specific protein. Eukaryotic mRNA is structured to last several hours in the cytoplasm, which is in stark contrast to the ephemeral nature of prokaryotic mRNA. This stability allows the mRNA to be efficiently used for protein synthesis before it is degraded.