Answer:
a) introns
Step-by-step explanation:
In molecular terms, a gene can be defined as a segment of DNA that is expressed to give a functional product, which can be an RNA or a polypeptide. Large amounts of non-coding DNA can be found within the majority of eukaryotic genes. These genes have a divided structure in which the segments of coding sequence (called exons) are separated by non-coding sequences (called introns). The complete gene is transcribed to produce a long molecule of RNA (called pre-RNAm) which will suffer a series of changes before leaving the nucleus. One of these modifications is called splicing, in which the introns are removed. Therefore, only exons are included in the RNAm.
The biochemical analysis of nuclear extracts has revealed that splicing occurs in big complexes, called spliceosomes, formed by small nuclear ribonucleoproteins (snRNPs) and 5 types of small size nuclear RNA (RNAsn).