After transcription begins, several steps must be completed before the fully processed mRNA is ready to be used as a template fo
r protein synthesis on the ribosomes. Which three statements correctly describe the processing that takes place before a mature mRNA exits the nucleus?
a. Noncoding sequences called introns are spliced out by molecular complexes called spliceosomes.
b. A cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mRNA.
c. Coding sequences called exons are spliced out by ribosomes.
d. A translation stop codon is added at the 3' end of the pre-mRNA.
e. A poly-A tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mRNA.
This may be rong, however I think this needs to happen before the mRNA can leave the nucleus. The cap helps prevent the mRNA from being destroyed by the cell itself once it leaves the nucleus.
