Here is the question: How many GTP are necessary to synthesize 2 linear peptides of 11 amino acids each using an in vitro prokaryotic system? Assume the tRNAs provided are already loaded with their proper amino acids. All 3 steps of the protein synthesis reaction must be completed.
My answer was 46. I thought that translation initiation uses 2 GTPs (the GTPs on eIF2 and eIF5B are hydrolyzed). Elongation involves 2 GTPs for each amino acid after the first methionine (the GTPs on EF1𝛂 and EF2 are hydrolyzed) - there are 10 amino acids left, so 2x10=20 GTPs are used. Termination involves 1 GTP (the GTP on eRF3 is hydrolyzed). So for one linear chain of 11 amino acids, 2+20+1=23 GTPs are used, and for 2 chains, 46 GTPs are used.
The correct answer is 44. I'm not sure where in my reasoning I went wrong. In what steps were there less GTPs used, and which proteins instead did not actually have GTP hydrolysis? Thank you.