Rna Splicing Puns

Is their a chemical marker or something like that that indicates which is which? Also how does the protein(s) “cut” the introns out and then bind the Exons together so that the structure of the mature RNA is retained?

Edit: Exon

Hey guys, I've just been learning the RNA-seq pipeline and becoming familiar with it. One of my colleagues mentioned that RNA-seq can be used to visualise & quantify alternative splicing, but i'm quite confused how it does that. Can anyone help me understand?

I've been taking an immunology course on coursera and we have gotten to antibody light and heavy chain gene rearrangement. What strikes me is that the process of selecting variable, joining and constant regions could be done by rna splicing alone (some the splicing is rna) like other proteins instead of gene rearrangement. Is there a reason cells prefer the gene rearrangement?