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Hydrolysis of ATP to ADP + Pi

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For problems 6-8, assume standard conditions of pH 7 and 25C, unless otherwise stated, and assume equilibrium constants in which any [H+] and [H2O] terms have been incorporated into the constant, i.e., you don't have to use [H+] in any of the calculations.

6. The equilibrium constant for the reaction of ADPS and 1,3-diphosphoglycerate to give ATPS and 3-phosphoglycerate is 400. What is the G´ for this reaction?

7. Muscles are powered by the hydrolysis of ATP to ADP + Pi. The G´ for hydrolysis of ATP is -8500 cal mol-1. At the beginning of exercise the G for the reaction is -13,200 cal mol-1, and the ATP concentration is 10 times that of ADP. How much will this differ from the G for the reaction when exercise has reduced the ATP to 10-4 M and ADP is10-3 M with Pi at 0.04 M?

8. An amino acid binding protein involved in transport of the amino acid across membranes was isolated from E. coli. Equilibrium dialysis measurements at 25 and 37C yielded dissociation constant (Ks) values of 8.8 x 10-6 M and 3.0 x 10-5 M, respectively, for the protein-ligand complex. Calculate
(a) G´ values for the binding reaction at 25C and 37C,
(b) H´ and S´ for the binding reaction assuming they are constant over this temperature range, and
(c) expected Ks at 30C.

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Stepwise explnation given to problems related to thermodynamics and equilibrium constant for biochemical reactions

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Energies Associated With Movement of Ca2+ Across Sarcoplasmic Reticulum using Membrane Potentials and Calculations involving Calsequestrin

Problem:
(a) In skeletal muscle the Ca+2 concentration is controlled by the SR (sarcoplasmic reticulum). At rest, the Ca+2 pump of the SR can maintain a concentration gradient of 0.5 mM inside SR / 0.1 µM cytoplasm (aka, outside the SR). How much energy is stored in this gradient; ignore the effects of charge.

(b) The pump can be summarized by these two equations:

2 Ca+2 outside ---> 2 Ca+2 inside

ATP ---> ADP + Pi

Given the resting concentration of Ca+2 above and ATP= 2.5mM, ADP= 0.5 mM and Pi= 0.5 mM, how much energy is required to move the 2 Ca+2 ions into the SR per cycle and how much energy is released by ATP hydrolysis. ( deltaG' ATP = -7,700 cal/mol)

(c) The SR also contains a Ca+2 binding protein "calsequestrin" which reduces the actual SR free [Ca+2] from 20 mM, which it would be without the presence of the protein, to 0.5 mM; the figure given above. From the info given, total SR Ca+2 and free SR Ca+2, and an estimate of 90% saturation of binding sites under these conditions, estimate the Ka of calsequestrin for Ca+2.

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