(N/A) The concept of an adapter molecule that could read the genetic code and bind to specific amino acids during translation was proposed by Francis Crick in $1961$.
$tRNA$ was known before the genetic code was deciphered and was initially called $sRNA$ (soluble $RNA$),but later its role as an adapter molecule was established.
Structure of $tRNA$:
$1$. The $tRNA$ has a secondary structure that resembles a clover leaf.
$2$. Its three-dimensional structure is an inverted $L$-shaped molecule.
$3$. $tRNA$ contains specific regions:
$(i)$ Anticodon loop: It contains bases complementary to the codon on $mRNA$.
$(ii)$ Amino acid acceptor end: This end binds to the specific amino acid.
$(iii)$ $T\psi C$-loop ($T$-loop): It helps in binding to the ribosome.
$(iv)$ $D$-loop: It helps in binding to aminoacyl-tRNA synthetase.
$(v)$ Variable loop: It varies in both nucleotide composition and length.
$tRNAs$ are specific for each amino acid. For initiation,there is a specific $tRNA$ referred to as the initiator $tRNA$. There are no $tRNAs$ for stop codons.