In elongation, where is energy used?

• A. Steps 1 and 3
• B. Step 2
• C. Step 4
• D. All steps

Answer: (A)

In elongation, energy is used during the two GTP-dependent parts of each cycle: getting the correct aminoacyl-tRNA to the A site and moving the ribosome along the mRNA after the peptide bond forms. The delivery of the charged tRNA to the A site is driven by a GTP‑bound elongation factor that hydrolyzes GTP, helping ensure correct pairing and readiness for peptide bond formation. After the bond forms, another GTP‑dependent step uses energy to translocate the ribosome, shifting the tRNAs and advancing to the next codon. The actual peptide bond formation itself does not consume GTP in this cycle. So the energy use is tied to tRNA delivery and translocation, which corresponds to the energy-requiring parts of the elongation process.