Final answer:
A spliceosome contains proteins and snRNAs that recognize and remove introns from pre-mRNA, ensuring the resulting mRNA consists exclusively of exons for correct protein synthesis.
Step-by-step explanation:
The spliceosome is a complex of enzymes that plays a critical role in gene expression by splicing out introns from a pre-mRNA transcript. This ensures that the pre-mRNA is modified into a mature mRNA molecule that contains only the coding sequences, known as exons. The spliceosome is composed of proteins and RNA molecules called small nuclear RNAs (snRNAs). These snRNAs help the spliceosome recognize the intron's 5' and 3' ends, allowing for the precise removal and degradation of introns while the pre-mRNA is still in the nucleus. It is crucial for this process to be precise; even a single nucleotide error can alter the resulting protein's functionality. Spliceosomes work by recognizing specific sequences at the intron's borders, typically GU at the 5' end and AG at the 3' end, and then catalyzing the excision of the intron and the ligation of the exons.