Some unfavorable biochemical reactions require hydrolysis of ATP to ADP and inorganic phosphate to drive them, while other unfavorable biochemical reactions use the hydrolysis of ATP to AMP and pyrophosphate to drive them. Explain, thermodynamically, how these two hydrolysis reactions are different for a cell. In other words, why do some reactions hydrolyze to ADP while others hydrolyze to AMP, thermodynamically speaking?

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Elin HesselLv2

28 Sep 2019

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Creatine (Cr) is made in the liver and kidneys and then transported to the muscles, where it serves as a high energy storage compound via phosphorylation by creatine kinase. Two forms of this enzyme exist, mitochondrial and cytoplasmic. In mitochondria there is net synthesis of creatine phosphate (CrP). In the cytosol, the phosphate is transferred from CrP to ADP to supply ATP to power the muscles. Table 3.2 of your G&G text lists ÎGËÌ for hydrolysis of creatine phosphate: -43.3 kJ/mol at 25Â°C. creatine phosphate + H2O ----> creatine + Pi

a. Calculate the KeqÍ for this hydrolysis.

c. In mouse muscle cells at 25Â°C, [Cr] is 10 mM, and [CrP] is 20 mM. What concentration of Pi would be needed to maintain this level of phosphorylation by reversal of the hydrolysis reaction? Is this concentration of Pi a reasonable expectation? Why?

d. Coupling ATP hydrolysis (ÎGËÍ-35.7 kJ/mol at 25Â°C) to an unfavorable reaction is often used to drive biochemical reactions. Write the chemical equations for the CrP reverse hydrolysis and ATP hydrolysis and add them together to give the coupled reaction. Then calculate ÎGËÍfor the coupled reaction. Is this reaction favorable? Justify your answer.

e. Considering ÎGÍin the muscle cells rather than under 1M standard state conditions, what ratio of ATP/ADP would be needed inside mitochondria to make the coupled reaction for CrP synthesis produce the concentrations of Cr and CrP observed in mouse muscle? Is this ratio reasonable? Why?

crimsonduck531

Subject: Cell Biology

Why do some books state that the standard free energy for the hydrolysis of the gamma-phosphate group (the one furthest from the ribose) of ATP is different from the standard free energy change for the hydrolysis of the beta phosphate group (the middle phosphate group)? (my textbook shows the same standard free energy change for the hydrolysis of these two groups and that the textbook uses kcal/mol as the unit for free energy (some textbooks use kJ/mol)).

ultramarinecricket621

Subject: Cell Biology Why do some books state that the standard free energy for the hydrolysis of the gamma-phosphate group (the one furthest from the ribose) of ATP is different from the standard free energy change for the hydrolysis of the beta phosphate group (the middle phosphate group)? (my textbook shows the same standard free energy change for the hydrolysis of these two groups and that the textbook uses kcal/mol as the unit for free energy (some textbooks use kJ/mol)).

indigolouse638

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