Final answer:
Eukaryotic mRNAs are generated by cleavage and polyadenylation, which involve the addition of a poly(A) tail to the mRNA. Cleavage is carried out by an endonuclease enzyme between specific sequences, and then a poly(A) polymerase enzyme adds a string of adenine residues. This process protects the mRNA from degradation and facilitates its export to the cytoplasm.
Step-by-step explanation:
Eukaryotic mRNAs undergo a process called cleavage and polyadenylation to generate their 3' ends. This process involves the addition of a poly(A) tail to the mRNA. During cleavage, an endonuclease enzyme cuts the pre-mRNA between an AAUAAA consensus sequence and a GU-rich sequence, leaving the AAUAAA sequence.
Then, a poly(A) polymerase enzyme adds a string of approximately 200 adenine residues, known as the poly(A) tail. The poly(A) tail protects the mRNA from degradation and signals the export of the transcript to the cytoplasm.