What is mRNA splicing and why is it important?

mRNA splicing is a form of post-transcriptional modification of the mRNA transcript. DNA is made up of coding regions called Exons. These determine the amino acid sequence of a polypeptide chain during protein synthesis. However, it is also made up on non-coding regions called Introns that have no use when it comes to protein synthesis. Transcription of DNA produces pre-mRNA that has both Introns and Exons. To make mature mRNA the all Introns must be removed by a splicesosome made up of snRNA's that recognize the Intron-Exon border; these effectively 'cut' the Intron out and ligate the Exon ends together. This creates mature mRNA made up of just Exons. This is important because our DNA is made up of around 23,000 genes yet we have many more proteins than genes, so how is this possible? Splicing allows one gene to code for multiple proteins by altering which exons will remain in the mature mRNA transcript . This will change the sequence of amino acids in the primary structure of the protein which will in turn effect protein folding; giving rise to proteins with different structures with different purposes from a single gene.