Transfer RNA (tRNA) is a ribonucleic acid about 50-60 nucleotides long. When a tRNA gets "charged" by covalent addition of its cognate amino acid, to which end of the tRNA is the amino acid attached?

The C-C-A tail at the 3' end of the tRNA molecule.

Explanation:

The tRNA is a molecule that is also involved in the process of translation. It does this by bringing amino acids to the ribosomes for polypeptide synthesis. Before this, the tRNA has to be charged with the amino acid to be transported with the help of aminoacyl tRNA synthetases.

One end of the tRNA binds to a specific amino acid at its attachment region and the other end contains an anticodon that binds to the mRNA codon. The attachment region is at the C-C-A tail; a cytosine-cytosine-adenine sequence found at the 3' end of the tRNA molecule with the amino acid being covalently bonded to the 3' hydroxyl end of this tail.