Final answer:
Spliceosomes, composed of proteins and snRNAs, are the enzyme complexes responsible for catalyzing the splicing reaction to remove introns from pre-mRNA transcripts.
Step-by-step explanation:
The enzymes that carry out the splicing reactions are part of a complex called the spliceosome. The spliceosome is responsible for precisely removing introns from the primary RNA transcript in a process called pre-mRNA splicing. This complex is made up of proteins and RNA molecules known as small nuclear RNAs (snRNAs). These snRNAs form small nuclear ribonucleoproteins (snRNPs) that bind to specific sites on the mRNA. The spliceosome then orchestrates the splicing process by bringing together the correct splice sites, cutting the transcript at those points, and ligating the exons together to form the mature mRNA.