The enzyme that charges RNA molecules with appropriate amino acids is aminoacyl-tRNA synthetase.

Here's how it works:

1. Recognition: Each aminoacyl-tRNA synthetase is specific for a particular amino acid and its corresponding tRNA.

2. Activation: The enzyme binds the amino acid and ATP, using the energy from ATP to activate the amino acid.

3. Attachment: The activated amino acid is then attached to the 3' end of the specific tRNA molecule.

This process, called aminoacylation, ensures that the correct amino acid is attached to the correct tRNA, which is essential for accurate protein synthesis.