This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': 'Some mRNA has self-splicing activity. The removal of introns is/are done by \nSelect and explain. \nA. Occur in intron that from Ribozyme, B. Self-splicing introns, C. Lariats intermediates are formed, D. All of these', 'role': 'user'}, {'content': "Answer: D \nExplanation: In\xa0molecular biology\xa0and\xa0genetics,\xa0splicing is a modification of an RNA after transcription, in which introns are removed and exons are joined. This is needed for the typical\xa0eukaryotic\xa0messenger RNA before it can be used to produce a correct protein through\xa0translation.\xa0For many eukaryotic introns, splicing is done in a series of reactions which are\xa0catalyzed\xa0by the\xa0spliceosome\xa0a complex of small nuclear ribonucleoproteins (snRNAs), but there are also self-splicing introns.\n\nSelf-splicing\n\nSelf-splicing occurs for rare introns that form a\xa0ribozyme,\xa0performing the functions of the spliceosome by\xa0RNA alone.\nThere are three kinds of self-splicing introns,\xa0Group I, Group II\xa0and\xa0Group III.\xa0Group I and II introns\xa0perform\xa0splicing similar to the spliceosome without requiring any protein.\xa0This similarity suggests that Group I and II introns may be evolutionarily related to the spliceosome. Self-splicing may also be very ancient and may have existed in an\xa0RNA world\xa0present before protein.\nAlthough the two splicing mechanisms described below do not require any proteins to occur, 5 additional RNA molecules and over 50 proteins are used and hydrolyzes many ATP molecules. The splicing mechanisms use ATP in order to accurately splice mRNA's. If the cell were to not use any ATP's the process would be highly inaccurate and many mistakes would occur.\nTwo transesterifications characterize the mechanism in which\xa0group I introns\xa0are spliced :\n\n\n3' OH of a free guanine, nucleoside (or one located in the intron) or a nucleotide cofactor (GMP, GDP, GTP) attacks phosphate at the 5' splice site.\n3' OH of the 5 'exon becomes a nucleophile and the second transesterification results in the joining of the two exons.\n\n\nThe mechanism in which\xa0group II introns\xa0are spliced (two transesterification reaction like group I introns) is as follows :\n\n\nThe 2'OH of a specific adenosine in the intron attacks the 5' splice site, thereby\xa0forming the lariat.\nThe 3'OH of the 5' exon triggers the second transesterification at the 3' splice site thereby joining the exons together.\n\n\nSpliceosomal and self-splicing transesterification reactions occur via two sequential transesterification reactions. First, the 2' OH of a specific\xa0branch point nucleotide within the intron that is defined during spliceosome assembly performs a nucleophilic attack on the first nucleotide of the intron at the 5' splice site forming the\xa0lariat intermediate.\xa0Second, the 3' OH of the released 5' exon then performs a nucleophilic attack at the last nucleotide of the intron at the 3' splice site thus joining the exons and releasing the intron lariat.'", 'role': 'assistant'}]