Expansion
Messenger carries, transfer delivers, ribosomal builds
Expansion
The three classical types, in order of abundance:
- rRNA, about 80 per cent - structural and catalytic component of the ribosome. It is a ribozyme: the peptidyl transferase activity is RNA, not protein
- tRNA, about 15 per cent - the adaptor, with an anticodon at one end and the amino acid at the 3’ CCA end. Cloverleaf secondary structure
- mRNA, about 5 per cent - carries the code, and is the least abundant but most heterogeneous
“rRNA builds, tRNA brings, mRNA is the blueprint.”
Regulatory RNAs
- microRNA (miRNA) - binds mRNA to repress translation or trigger degradation. Dysregulated in cancer
- small interfering RNA (siRNA) - mediates RNA interference, and the basis of a class of therapeutics
- snRNA - part of the spliceosome, removing introns
- lncRNA - includes XIST, which silences one X chromosome in females
Eukaryotic mRNA processing, which prokaryotes lack: a 5’ cap, 3’ poly-A tail, and splicing to remove introns. Alternative splicing lets one gene produce many proteins, which is why humans have far more proteins than genes.
Clinical relevance: mRNA vaccines exploit this directly, and thalassaemia can result from splice site mutations rather than coding mutations.