An Important Difference Between a Class I and Class II

Question

An important difference between a class I and class II aminoacyl-tRNA synthetase is:
A) The two classes proceed through different aminoacyl-AMP intermediates.
B) Class I synthetases first attach the amino acid to the 2'-hydroxyl on ribose, whereas class II attach them to the 3'-hydroxyl.
C) Class I synthetases attach amino acids to the 5'-end of the tRNA, whereas class II attach them to the 3'-end.
D) The 5'-end of the tRNA molecule is phosphorylated only for those tRNAs recognized by class I synthetases.
E) None are true.

Accepted Answer

Class I aminoacyl-tRNA synthetases attach the amino acid to the 2'-hydroxyl group of the ribose in the tRNA, whereas class II enzymes attach it to the 3'-hydroxyl group. This difference is fundamental in the mechanism of how tRNAs are charged with their respective amino acids.