Genetics: Analysis and Principles 5th Edition by Robert Brooker

Exercise 31

In the splicing of group I introns shown in Figure 12.20, does the 5 end of the intron have a phosphate group Explain.FIGURE 12.20 Mechanisms of RNA splicing. Group I and II introns are self-splicing. (a) The splicing of group I introns involves the binding of a free guanosine to a site within the intron, leading to the cleavage of RNA at the 3 end of exon 1. The bond between a different nucleotide in the intron strand (in this case, guanine) and the 5 end of exon 2 is cleaved. The 3 end of exon 1 then forms a covalent bond with the 5 end of exon 2. (b) In group II introns, a similar self-splicing mechanism occurs, except that the 2 OH group on an adenine nucleotide (already within the intron) begins the catalytic process. (c) Pre-mRNA splicing requires the aid of a multicomponent structure known as the spliceosome.