tRNA is responsible for reading the codon of messenger RNA and insertion of codon specific amino acids during translation. The structure consists of hydrogen bonded stems and associated loops, which often contain nucleotides with modified bases (e.g. inosine[I], ribothymidine [T], pseudouridine[Ψ], methylguanosine[D]). It is localized in cytoplasm. rRNA is the RNA component of the ribosome, and is essential for protein synthesis in all living organisms.The ribosomal RNAs form two subunits, the large subunit and small subunit. For prokaryotes, the three Escherichia coli rRNA molecules are used as size standards; they have sedimentation coefficients of 5S, 16S, and 23S. Eukaryotic rRNA molecules are generally larger and there are four of them. Rat liver rRNA molecules are used as standards; the S values and the average number of nucleotides in parentheses are 5S (120), 5.8S (150), 18S (2100), and 28S (5050), respectively. It is localized in ribosome.