The accuracy of charging a tRNA with the correct amino acid is about 1.5 × 10-5, which is lower than the error rate of translation (which is about 2 to 5 × 10-4)
Aminoacyl-tRNA synthetases use both kinetic and chemical proofreading. What is the distinction between these two proofreading methods?
What will be an ideal response?
Ans: Kinetic proofreading does not involve the reversal of a chemical reaction. Instead, it relies on slowing a step so that the wrong substrate (which may bind less stably) dissociates before the chemical reaction has a chance to occur. An example is the conformational change that occurs if the aminoacyl-tRNA synthetase binds the correct tRNA, which accelerates the aminoacylation step. If the wrong tRNA binds, the conformational change does not occur and usually the wrong tRNA dissociates from the enzyme before the aminoacyl-adenylate is transferred. Chemical proofreading involves scrutinizing the product of a chemical reaction, and if incorrect, the reaction is reversed. Some tRNA synthetases will hydrolyze the aminoacyl-adenylate if the wrong amino acid is picked up by the synthetase, and other synthetases hydrolyze the aminoacyl bond after the amino acid has been transferred to the tRNA. The enzymes recognize wrong amino acids by the distortion of the active site of the enzyme.
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