55) Which one of the following statements about RNA processing is true? A) RNA splicing can be catalyzed by tRNA. B) A primary transcript is often much shorter than the final RNA molecule that leaves the nucleus. C) Exons are cut out before mRNA leaves the nucleus. D) Ribozymes may function in RNA splicing.

Gene expression involves two major stages: transcription and translation. Transcription involves the production of an mRNA molecule which is called a transcript. However, when this RNA transcript is newly made, it is regarded as pre-mRNA. It needs to undergo certain procedures collectively called RNA processing in order to be considered a mature RNA.

In an eukaryotic cell, pre-mRNA undergoes three major steps to become matured mRNA. These steps are:

1. Capping at the 5' end, which involves the addition of a nucleoside to the 5' end of the mRNA molecule.

2. Polyadenylation, which involves adding Adenine nucleotides to the 3' end of the mRNA molecule.

3. Splicing, which involves removal of the non-coding regions of the gene called EXONs from the coding region called INTRON. This process is carried out by an enzyme called SPLICEOSOMES.

RNA processing in eukaryotes occurs before the mRNA molecule leaves the nucleus for the cytoplasm in order to be translated. At the end of the RNA processing, the mature RNA molecule that leaves the nucleus is shorter than the pre-mRNA molecule due to the removal of exons during splicing.