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Biochemistry

9th Edition

ISBN:9781319114671

Author:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Publisher:Lubert Stryer, Jeremy M. Berg, John L. Tymoczko, Gregory J. Gatto Jr.

Chapter1: Biochemistry: An Evolving Science

Section: Chapter Questions

Problem 1P

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The formation of acetyl-CoA from acetate is an ATP-driven reaction:

Acetate + ATP + CoA ⇌ Acetyl CoA + AMP + PPi

Calculate ΔG°' for this reaction given that the ΔG°' for the hydrolysis of acetyl CoA to acetate and CoA is −31.4 kJ mol⁻¹ (−7.5 kcal mol⁻¹) and that the ΔG°' for hydrolysis of ATP to AMP and PPi is −45.6 kJ mol⁻¹ (−10.9 kcal mol⁻¹).

ΔG°'reaction = ________ kJ mol⁻¹

The PPi formed in the preceding reaction is rapidly hydrolyzed in vivo because of the ubiquity of inorganic pyrophosphatase. The ΔG°' for the hydrolysis of pyrophosphate (PPi) is −19.2 kJ mol⁻¹ (−4.665 kcal mol⁻¹). Calculate the ΔG°' for the overall reaction, including pyrophosphate hydrolysis.

ΔG°'reaction with PPi hydrolysis = ________ kJ mol⁻¹

What effect does the presence of pyrophosphatase have on the formation of acetyl CoA?

- [ ] It does not affect the overall reaction.
- [ ] It brings the overall reaction closer to equilibrium.
- [ ] It makes the overall reaction even more exergonic.
- [ ] It makes the overall reaction even more endergonic.

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