Energetics of Biological Reactions and ATP - MCAT Chemical and Physical Foundations of Biological Systems

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Question

ATP stores energy through its ability to lose a phosphate group to form ADP in the following reaction

At body temperature, the thermodynamic values for ATP hydrolysis are as follow.
ΔG = –30kJ/mol
ΔH = –20kJ/mol
ΔS = 34kJ/mol

Glycolysis is an energy-liberating process (ΔG = –218kJ/mol, ΔH = –20 kJ/mol) that is coupled with the conversion of two ADP molecules into two ATP molecules according to the following reaction.

The formation of peptide bonds requires 17kJ/mol of energy. It also requires the energy of three ATP molecules. How many ATP molecules are required to synthesize a protein containing 550 peptide bonds?

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Answer

Since we know that three ATP molecules per bond are required, 1,650 ATP molecules are needed. However, we also know that 17kJ/mol of additional energy is required for each bond. This energy must come from ATP molecules. The only choice that is greater than 1,650 is 1,962.

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