How does aminoacyl-tRNA synthetase charge tRNA with its amino acid?

• A. ATP energy is used by aminoacyl-tRNA synthetase to attach the amino acid to tRNA, releasing two phosphates
• B. GTP directly attaches amino acid to tRNA
• C. The tRNA attaches amino acid by itself
• D. The ribosome attaches amino acid to tRNA

Answer: (A)

Charging tRNA with its amino acid relies on an energy-dependent, two-step process carried out by aminoacyl-tRNA synthetase. First, the amino acid is activated by reacting with ATP to form an aminoacyl-AMP intermediate, and pyrophosphate (two phosphate groups) is released. This activation step uses ATP’s high-energy phosphate bonds to create a highly reactive intermediate. Next, the amino acid from aminoacyl-AMP is transferred to the 3′ end of the tRNA, producing aminoacyl-tRNA and releasing AMP. The overall energy input comes from ATP hydrolysis, and the ribosome isn’t involved in the charging step. Because of this reliance on ATP to drive the activation and transfer, the option stating that ATP energy is used to attach the amino acid to tRNA, releasing two phosphates, is the correct description.