Here's a breakdown:

1. Transcription: DNA is transcribed into a pre-mRNA molecule. This pre-mRNA contains both exons (coding regions) and introns (non-coding regions).

2. Splicing: The introns are removed from the pre-mRNA, and the exons are joined together to form a continuous coding sequence. This mature mRNA is now ready to be exported from the nucleus to the cytoplasm.

So, what gets "cut out" are the introns.

Here's a simple analogy:

Imagine you have a book with chapters (exons) and some pages in between those chapters (introns). You want to read the book but only the chapters are important. You cut out the pages in between the chapters (introns) and then tape the chapters together (exons). Now you have a readable book only containing the information you need.

The splicing process is crucial for generating functional mRNA. It allows for:

* Removal of non-coding sequences: Introns are non-coding, so they don't contain instructions for making proteins. Removing them ensures that only the coding sequences are translated.

* Alternative splicing: Different introns can be removed, leading to the production of different versions of a protein from the same gene. This increases the diversity of proteins that can be made from a single gene.

Let me know if you have any other questions!