after transcription begins, several steps must be completed before the fully processed mrna is ready to be used as a template for protein synthesis on the ribosomes. which three statements correctly describe the processing that takes place before a mature mrna exits the nucleus? view available hint(s)for part c after transcription begins, several steps must be completed before the fully processed mrna is ready to be used as a template for protein synthesis on the ribosomes.which three statements correctly describe the processing that takes place before a mature mrna exits the nucleus? a translation stop codon is added at the 3' end of the pre-mrna. coding sequences called exons are spliced out by ribosomes. noncoding sequences called introns are spliced out by molecular complexes called spliceosomes. a cap consisting of a modified guanine nucleotide is added to the 5' end of the pre-mrna. a poly-a tail (50-250 adenine nucleotides) is added to the 3' end of the pre-mrna.
