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. 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.