Question

During translation initiation in prokaryotes, GTP is required for

• A. Formation of formyl met-tRNA
• B. Binding of 30S subunit of ribosome with mRNA
• C. Association of 30S mRNA with formyl-met-tRNA
• D. Association of 50S subunit of ribosome with initiation complex

Answer 1

Answer: (C)

Association of 30S mRNA with formyl-met-tRNA

Formyl-met-tRNA is formed by the addition of methionine to tRNAfMet (formyl-methionine specific-tRNA) by the fMet-tRNA synthetase to produce methionine tRNA and then the transfer of formyl group from N(10)-formyltetrahydrofolate to the amino group of the Met residue to produce N-formyl methionine tRNA. Option A is wrong. The first step in translation initiation is binding of 30S ribosomal subunit to two initiation factors, IF-1 and IF-3. Factor IF-3 prevents the 30S and 50S subunits from combining prematurely. The mRNA then binds to the 30S subunit. This makes option B wrong. This is followed by binding of complex consisting of the 30S ribosomal subunit, IF-3, and mRNA with both GTP-bound IF-2 and the initiating formyl met-tRNA. Thus, option C is correct. The pairing of the anticodon of tRNA with the mRNAs initiation codon induces binding of 50S ribosomal subunit. This makes option D incorrect. Binding of 30S ribosomal subunit with fmet-tRNA requires GTP; option C is correct.

Thus, the correct answer is option C.