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.
Eukaryotes have a nucleus with a membrane, larger ribosomal subunits, usually reproduce sexually, and may not have a cell wall. Prokaryotes have no membrane around the nucleus, smaller ribosomal subunits, reproduce asexually, and do have cell walls.
