Table 1

Types, size and function of RNA

Protein coding or non-coding	Type of RNA	Size (number of nucleotides)	Function
Coding	Messenger RNA (3%–5% of total)19	Variable	Translated into proteins by ribosomes.
Non-coding structural and catalytic	Ribosomal RNA (80% of total)19	Four subunits (120, 160, 1900 and 4700 nucleotides)	Facilitates mRNA translation into protein.
Non-coding structural and catalytic	Transfer RNA19	80	Collects amino acids and delivers to ribosome to make protein.
Non-coding	Small nuclear and small nucleolar RNA (snRNA/snoRNA)20	60–300	Control mRNA and rRNA splicing.
Regulatory non coding	MicroRNA (miRNA)12	19–24	Regulate gene expression at a post-transcription level by translational repression or mRNA degradation.
	Piwi-interacting RNA19	>23	Gene silencing of transposons and repetitive sequences.
	Long non-coding RNAs12	>200	Many and broad functions including: gene regulation, chromosomal dynamics and telomere biology.