There are many unique types of RNA in cells involved in transcription that may act on their own or in complexes with proteins.

A ribozyme is a special enzyme formed from RNA (rather than protein) that can catalyze a chemical reaction. Some ribosomal RNAs (rRNAs) are ribozymes that link amino acids together to form a protein.

The spliceosome is a protein-RNA complex that acts as an enzyme during pre-mRNA processing. This complex removes introns from pre-mRNA and joins the remaining exons to produce a mature mRNA molecule. Spliceosomes are made up of many small nuclear ribonucleoproteins (snRNPs), which are complexes of proteins and RNA. Each snRNP is itself a complex of proteins and a special type of RNA found only in the nucleus called small nuclear RNA (snRNA).

Key Points

• Ribozymes are enzymes formed from RNA instead of proteins.

• Spliceosomes are protein-RNA complexes that catalyze the removal of introns and joining of exons in pre-mRNA strands.

• Spliceosomes are composed of many protein-RNA complexes called snRNPs, which are themselves composed of a specific type of RNA known as snRNA.

Key Terms

Ribozyme: An enzyme formed from RNA instead of proteins.

Enzyme: A molecule that catalyzes (or accelerates) a biochemical reaction.

Spliceosome: A protein-RNA complex that acts as an enzyme during pre-mRNA processing to remove introns and join together exons.

Small nuclear ribonucleoproteins (snRNPs): Complexes of protein and RNA that are the building blocks of spliceosomes.

Small nuclear RNAs (snRNAs): Nuclear RNAs that make up the RNA component of snRNPs.