Question: 129. Which of the following are the post-transcriptional events in an eukaryotic cell?
A. Transport of pre-mRNA to cytoplasm prior to splicing.
B. Removal of introns and joining of exons.
C. Addition of methyl group at 5^{\prime} end of hnRNA.
D. Addition of adenine residues at 3′ end of hnRNA.
E. Base pairing of two complementary RNAs.
Choose the correct answer from the options given below:
(1) A, B, C only
(2) B, C, D only
(3) B, C, E only
(4) C, D, E only
Answer: Option (2)
Explanation:
Post-transcriptional events are the modifications that occur to the primary RNA transcript (hnRNA) in eukaryotic cells before it becomes a mature mRNA.
Removal of introns and joining of exons by splicing is a key post-transcriptional event.
Addition of a methylated guanosine cap at the 5^{\prime} end of hnRNA, known as capping, is another post-transcriptional modification.
Addition of adenine residues at the 3′ end of hnRNA, called polyadenylation, is also a post-transcriptional process.
Transport of pre-mRNA to the cytoplasm occurs only after splicing and processing, so statement A is incorrect.
Base pairing of complementary RNAs is related to RNA interference and is not a post-transcriptional modification of hnRNA.
Therefore, the correct post-transcriptional events are B, C, and D.