Map Group I introns are a class of self-splicing ribozymes. The splicing mechani

Question

Map Group I introns are a class of self-splicing ribozymes. The splicing mechanism involves two transesterification reactions. (a) Identify the nucleophile for the transesterification reaction that is the first step in splicing group I introns such as L-19 IVS. Identify the nucleophile by selecting it (click an atom: it will become highlighted in green). (b) Which of the following four statements correctly describes the splicing of group I introns? The 5? hydroxyl group of a guanine nucleoside forms a bond with the 5? end of the intron, and then the -5? hydroxyl group of the upstream exon forms a bond with the 3? end of the downstream intron. The 3? hydroxyl group of a guanine nucleoside forms a bond with the 3 end of the intron, and then the 3? hydroxyl group of the upstream exon forms a bond with the 5? end of the downstream exon. The 5? hydroxyl group of a guanine nucleoside forms a bond with the 3? end of the intron, and then the 5? hydroxyl group of the upstream exon forms a bond with the 3? end of the downstream exon. The 3? hydroxyl group of a guanine nucleoside forms a bond with the 5? end of the intron, and then the 3? hydroxyl group of the upstream exon forms a bond with the 5? end of the downstream exon.

Explanation / Answer

(a) In the given figure the 3' OH of G molecule acts as a nucleophile for the transesterification reaction.

(b) The statement which correctly describes the splicing of group 1 introns is:

The 3' hydroxyl group of a guanine nucleoside forms a bond with teh 5' end of the intron, and then the 3' hydroxyl group of teh upstream exon forms a bond with the 5' end of the downstream exon.

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