tRNA is an adaptor molecule. It occurs in the cytoplasm.
Post-transcriptional modifications in eukaryotes
For activation of amino acids, \
Initiation
• In prokaryotes, initiation requires the large and small ribosome subunits, the mRNA, initiation tRNA and three initiation factors (IFs).
• Activation of amino acid: Amino acids become activated by binding with aminoacyl tRNA synthetase enzyme in the presence of ATP.
• Transfer of amino acid to tRNA: The AA–AMP–Enzyme complex formed reacts with specific tRNA to form aminoacyl-tRNA complex. AA–AMP–Enzyme complex + tRNA → AA–tRNA + AMP + Enzyme.
• The cap region of mRNA binds to the smaller subunit of ribosome.
• The ribosome has two sites, A-site and P-site.
• The smaller subunit first binds to the initiator mRNA and then binds to the larger subunit so that initiation codon (AUG) lies on the P-site.
• The initiation tRNA, i.e., methionyl tRNA then binds to the P-site.
