Energy cost of adding one amino acid
How many high-energy phosphate bonds are used, in total, to add one amino acid to a growing polypeptide, counting tRNA charging and elongation?
Answer C: explanation for every choice
A
This counts only one GTP.
B
This counts only the two elongation GTPs, for delivering the tRNA and moving the ribosome.
C
Correct. Charging the tRNA converts ATP to AMP (2 bonds), and elongation uses 2 GTP.
D
This double-counts the charging step.
TakeawayAbout 4 high-energy bonds per amino acid: 2 for charging, 2 for elongation.
See your set score →
Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID bb185.