The ribosomal RNA (rRNA) is large macromolecular complex and main component of ribosomes that assemble the amino acids to form the protein whose sequence is encoded by a particular mRNA (messenger ribonucleic acid). The ribosomes act as workhorses in the process of translating the mRNA into protein. Protein synthesis commence at a start codon near 5' end of mRNA.
The primary enzymatic function of the ribosome is forming peptide bonds between adjacent amino acids in protein synthesis by the enzyme peptidyl transferase. The enzyme activity is not mediated by any ribosomal proteins. In eukaryotic cells the 28S component of the 60S ribosome subunit and in bacteria the 23S component of 50S ribosome subunits contains the peptidyl transferase and acts as ribozyme. Recent studies show that both the decoding center in 30S subunit and peptidyl transferase in 50S subunits is composed completely of rRNA.
Ribosomes are almost two-third of their mass in RNA and one-third in protein. Ribosomal RNAs are assumed to function as framework essential for the exact gathering of the ribosomal proteins and are only responsible for carrying out the significant steps in protein synthesis.