Overview rRNA ribosomal rRNA + protein = ribosome most abundant of all RNA types clinical importance shiga- and verotoxins bind to 28S rRNA inhibit eukaryotic protein synthesis tRNA transfer covalently attached to amino acids provides link between genetic code and a particular amino acid mRNA messenger carries DNA message from chromosome to translation by ribosome hnRNA or pre-mRNA heteronuclear present only in eukaryotes mRNA transcript prior to splicing contains introns and exons snRNA small nuclear present only in eukaryotes functions in splicing of mRNA in the nucleus Ribozymes present in eukaryotes and prokaryotes have intrinsic enzymatic activity miRNA micro ↓ translation by binding to 3'-UTR of target mRNA double-stranded RNA signals for degradation uses Dicer and RISC enzymes in processing often coded for in intron segments RNAi is a synthetic lab technique that takes advantage of miRNA pathway see Biochemical Model Systems topic