Final answer:
The spliceosome, which contains small nuclear RNAs (snRNAs), catalyzes the recognition and excision of introns during RNA splicing.
Step-by-step explanation:
During splicing, the molecular component of the spliceosome that catalyzes both the recognition of the splice site and the excision reaction is RNA. Specifically, the spliceosome is a complex mixture composed of proteins and RNA molecules known as small nuclear RNAs (snRNAs). These snRNAs play a critical role in the splicing process by recognizing the splice sites and catalyzing the removal of introns from the pre-mRNA to connect the exons, thereby forming a mature mRNA molecule. Specifically, it is composed of small nuclear RNAs (snRNAs) which are part of the spliceosome protein complexes. These spliceosomes recognize sequences at the 5' and 3' ends of the intron, facilitating the removal of introns from pre-mRNA transcripts during splicing.