Transcription results in a precursor to mRNA called pre-mRNA. This is modified first by adding a cap to the 5' end to stabilise it and adding a poly-A tail to the 3' end to stabilise the molecule and delay its degradation. The cap also helps the mRNA to bind to the ribosome.The RNA is then cut and rejoined at specific points by an enzyme-complex called a spliceosome. The non-coding sections of DNA removed are called introns and the coding sections that remain are called exons. The nucleotides can also be edited through base substitution, addition and deletion. Alternative splicing sites and RNA editing increases the number of proteins that can be made from a single pre-mRNA molecule