The key difference between spliceosomes and ribosomes is that spliceosomes catalyze the splicing of introns from pre-mRNAs while ribosomes catalyze the translation of mRNA to synthesize proteins.
Gene expression occurs via two main steps, known as transcription and translation. First, the nucleotide sequence of the gene is transcribed into a pre-mRNA molecule. Since gene sequence contains introns and exons, introns should be spliced off from the pre-mRNA molecule to produce a mature mRNA molecule containing only exons. Spliceosomes are ribonucleoprotein complexes that carry out splicing of introns from pre-mRNA molecules. Afterwards, the mature mRNA molecule leaves the nucleus and reaches the ribosomes in the cytoplasm for translation. Ribosomes are the cellular organelles that carry out protein synthesis from mRNA molecules. Both spliceosomes and ribosomes are multimolecular complexes that contain both RNA and proteins.
