AAT Bioquest

What are the steps of protein synthesis?

Posted February 24, 2023


There are five major steps of protein synthesis. The first step is the activation of the amino acids. For amino acids to become activated, tRNA must be charged through an aminoacyl RNA synthetase enzyme. This assists in the creation of the aminoacyl-AMP-enzyme complex, and results in the necessary ATP. The second step of protein synthesis is the transfer of amino acids to tRNA. During this step, the aminoacyl-AMP-enzyme complex becomes charged by reacting with a unique tRNA molecule. The amino acid is then transferred to a unique amino acid. Aminoacyl tRNA synthetase and the AMP molecule catalyze the esterification of tRNA and activate the molecule. The third step is the initiation of the polypeptide chain. The newly activated tRNA moves to the large subunit of the ribosome, which is attached to the mRNA transcript. Then, mRNA is bound to the 70S subunit and reads the codon on the mRNA. The charged tRNA molecule then moves into the aminoacyl site of the ribosome. Next, there is peptide formation between amino acids at the A-site and P-site. The amino acid at the P-site becomes removed from the tRNA and the formation of the peptide chain begins. The tRNA at the P-site moves to the exit site to leave the ribosome, and this process is repeated until mRNA is read until the termination codon stops it. In the fourth step (chain termination), a ribosome reaches one of the three termination codons (UAA, UAG, and UGA) and detaches from the mRNA. Once this occurs, translation is stopped. If there are errors in translation, mutations may arise leading to cancers. The last step in protein synthesis is protein translocation. Free poly-ribosomes directly release the growing peptide chain into the cytoplasm after the protein has been synthesized. Membrane-bound polyribosomes do not exit into the protein chain directly, and instead move into the lumen of ER for post-translational modifications.   

Additional resources

Protein Synthesis

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