Final answer:
Amino acids are attached to their tRNA molecules by enzymes called aminoacyl-tRNA synthetases during the process known as 'charging' the tRNA.
Step-by-step explanation:
Amino acids are attached to their tRNA molecules by a group of enzymes called aminoacyl-tRNA synthetases. The process of linking an amino acid to a tRNA is termed "charging" the tRNA. Each of the 20 amino acids has at least one specific aminoacyl-tRNA synthetase. These enzymes function by first binding and hydrolyzing ATP to catalyze a high-energy bond between an amino acid and adenosine monophosphate (AMP); a pyrophosphate molecule is then expelled. Subsequently, the activated amino acid is transferred to the tRNA, making it ready for protein synthesis.