Correct option is D
Statement Review:
Statement A: "RNA editing can occur via the deamination of cytosine residues, leading to formation of uracil and thus a change in coding sequence."
Correct: This is a true description of RNA editing. In this process, cytosine deamination forms uracil, which can lead to a change in the coding sequence, potentially altering protein function. This kind of RNA editing is observed in various organisms, including mammals, and plays a significant role in gene expression regulation.
Statement B: "The major spliceosomal complex mediates the removal of Group II introns."
Incorrect: The major spliceosomal complex indeed plays a key role in the removal of Group I and Group II introns, but Group II introns are primarily removed by self-splicing rather than being mediated by the spliceosome. While the spliceosome does handle Group I introns, Group II intron removal is a distinct process, not mediated by the spliceosome.
Statement C: "Trans-splicing events seen in trypanosomes allow the formation of multiple gene products by bringing together different combinations of exons of three or more genes."
Incorrect: While trans-splicing is a characteristic of certain organisms like trypanosomes, it typically involves splicing together two exons from different mRNAs, rather than from three or more genes. Thus, the description of trans-splicing in this statement is somewhat misleading, and the statement is not entirely correct.
Statement D: "Capping of eukaryotic mRNAs occurs exclusively in the nucleus of the cell."
Incorrect: While the 5' capping of eukaryotic mRNAs occurs in the nucleus, this statement implies that capping only occurs in the nucleus and never elsewhere. However, capping is an early event in the nucleus, but the statement does not fully capture the context of mRNA processing, and there are other post-transcriptional modifications that happen before mRNA export.
Conclusion:
Statement A is correct.
Statements B, C, and D are incorrect based on the details provided.
