Final answer:
The non-coding portions of DNA that are removed during the processing of mRNA are known as introns, and their removal is part of the splicing process required to produce functional proteins.
Step-by-step explanation:
The non-coding portions of DNA that are separated from the portions of DNA actually used during transcription are called introns. Introns are spliced out of the pre-mRNA before the mRNA is translated into protein. Eukaryotic genes are typically made up of exons, which encode for proteins, and introns, which do not encode for proteins and are non-coding. The process of removing introns and joining exons is called splicing, which is essential for producing functional mRNA that can be translated into a correct protein sequence. In humans, a large fraction of nuclear DNA consists of introns.