Describe the function of ribosomes in protein synthesis.

Ribosomes, which are made up of rRNA, are instrumental in the translation of mRNA into proteins. The ribosome has a large and a small subunit, which sandwich around a strand of mRNA. This mRNA attaches to the ribosome. The ribosome provides binding sites for two tRNA molecules. As each triplet codon of the mRNA moves through the ribosome, a specific tRNA is recruited, which has its own anticodon, complementary to certain mRNA codons. Attached to each tRNA is a specific amino acid. The two tRNA molecules which bind to the ribosome are in close proximity and their amino acids are held close together. A peptide bond is then formed between the amino acids by pepitdyl transferase.

As the mRNA moves through the ribosome, a growing chain of polypeptides is synthesised, which forms the primary protein structure. When the ribosome encounters a stop codon, the ribosome dissociates and no more amino acids are added to the polypeptide chain.