A process of protein biosynthesis occurs on ribosomes, involves mRNA, tRNA, enzymes, translation factors, and includes the steps of amino acid activation, translation initiation, elongation, and termination.
Free amino acids are activated with enzymes (aminoacyl-tRNA synthetase). They are attached to specific tRNA molecules resulting in the formation of aminoacyl-tRNA complexes.
At the stage of translation initiation, mRNA is attached to the small subunit of the ribosome. Initiation factors recognize the initial end of mRNA. The start codon (AUG) is placed in the P-region of the ribosome, while the large subunit of the ribosome completes the active site.
At the elongation stage, protein biosynthesis occurs. After the initiation step, methionine-tRNA is located in the P region of the ribosome. The next tRNA enters the A region of the ribosome. Its anticodon is complementary to the mRNA codon located next to the start codon and carries this tRNA amino acid corresponding to this codon. Next, the ribosome provides the formation of a peptide bond between amino acids located in A and P sites.
The elongation continues until one of the three stop codons occurs on the mRNA. Particular termination factors recognize these codons, attach to the ribosome, and facilitate ribosome dissociation.