Ribonucleic acid. Linear, generally single-stranded polymer, composed of ribose nucleotides, that is synthesized by transcription of DNA or by copying of RNA. The three types of cellular RNA – mRNA, rRNA, and tRNA – play different roles in protein synthesis.
A class of organisms composed of one or more cells containing a membrane-enclosed nucleus and organelles. This class constitutes one of three distinct evolutionary lineages (eubacteria, eukaryotes & archaea) of modern-day organisms. Includes all organisms except viruses and prokaryotes (mostly bacteria).