II.

Cellular RNA

In cellular organisms, RNA is a single-stranded polynucleotide chain, a strand of many nucleotides linked together. There are three types of RNA. Ribosomal RNA (rRNA) is found in the cell's ribosomes, the specialized structures that are the sites of protein synthesis). Transfer RNA (tRNA) carries amino acids to the ribosomes for incorporation into a protein. Messenger RNA (mRNA) carries the genetic blueprint copied from the sequence of bases in a cell's DNA. This blueprint specifies the sequence of amino acids in a protein. All three types of RNA are formed as needed, using specific sections of the cell's DNA as templates.