The ribosome is a key component to life; it is found in every living cell, and is responsible for translation of genetic information from messenger RNA to coded protein. Each ribosome consists of several large ribosomal RNA molecules, over fifty ribosomal proteins. A ribosome contains over 300,000 atoms. Many of core functional regions of the ribosome are nearly identical in structure and sequence in all living organisms. Comparison of ribosomal components reveals information about phylogeny and evolution.
Ribosomal RNA (rRNA) and ribosomal proteins (rProteins) associate to form two assemblies, the large (LSU) and small (SSU) subunits, both of which have highly conserved cores (Lake, et al., 1982; Noller, et al., 1981; Woese and Fox, 1977). The rProteins play critical roles in ribosomal assembly and function (Klein, et al., 2004).
Ribosomes are the workhorses of protein biosynthesis, the process of translating mRNA into protein. The mRNA comprises a series of codons that dictate to the ribosome the sequence of the amino acids needed to make the protein. Using the mRNA as a template, the ribosome traverses each codon (3 nucleotides) of the mRNA, pairing it with the appropriate amino acid provided by an aminoacyl-tRNA. aminoacyl-tRNA contains a complementary anticodon on one end and the appropriate amino acid on the other. The small ribosomal subunit binds to an AUG codon on the mRNA and recruits the large ribosomal subunit. The ribosome contains three RNA binding sites, designated A, P and E. The A site binds an aminoacyl-tRNA; the P site binds a peptidyl-tRNA (a tRNA bound to the peptide being synthesized); and the E site binds a free tRNA before it exits the ribosome. Protein synthesis begins at a start codon AUG near the 5' end of the mRNA. mRNA binds to the P site of the ribosome first.