Final answer:
Splice sites are located mostly in the introns because introns are non-coding sequences of DNA that do not contribute to protein coding. Splice sites and helper proteins facilitate the removal of introns and joining of exons during RNA splicing. Alternative gene splicing of introns allows for the production of multiple protein isoforms.
Step-by-step explanation:
Splice sites are located mostly in the introns because introns are non-coding sequences of DNA that do not directly contribute to the coding of proteins. Instead, introns play a role in the post-transcriptional modification of mRNA. During RNA splicing, introns are removed from the pre-mRNA molecule, and the exons (coding sequences) are joined together to form the final mRNA transcript.
This process is facilitated by splice sites, which are specific DNA sequences that mark the beginning and end of an intron. These sequences, along with other regulatory elements, help recruit helper proteins known as spliceosomes.
The spliceosomes recognize the splice sites and catalyze the removal of the intron and the joining of the exons through a complex series of molecular interactions. Ultimately, this alternative gene splicing of introns allows for the production of multiple protein isoforms from a single gene, increasing the diversity of protein function without the need for additional genes.