Final answer:
Spliceosomes are composed of small nuclear RNA (snRNA) and proteins, and they function in RNA splicing to process pre-mRNA into mature mRNA.
Step-by-step explanation:
Spliceosomes are essential complexes in the process known as RNA splicing, where introns are removed and exons are joined together in a newly synthesized pre-messenger RNA (pre-mRNA) transcript. These complexes are composed of small nuclear RNA (snRNA) and proteins. Specifically, they consist of small ribonuclear proteins (snRNPs), which include both snRNA and proteins. These snRNPs work together to recognize splicing sites and catalyze the splicing reactions, allowing for the correct processing of the pre-mRNA into mature mRNA, which can then be translated into proteins.