Enzymes normally enhance the rates of biochemical reactions by preferentially binding and stabilizing the transition states rather than either the substrates or the products of a reaction. The F|-subunit of ATP synthase does not fit this norm so well as tight binding to ATP rather than a transition state is employed to make ATP. Explain the binding-change model of the mechanism of ATP-synthase. How and why is the proton-motive force used in the reaction cycle of ATP synthase

Enzymes normally enhance the rates of biochemical reactions by preferentially binding and stabilizing the transition states rather than either the substrates or the products of a reaction. The F|-subunit of ATP synthase does not fit this norm so well as tight binding to ATP rather than a transition state is employed to make ATP. Explain the binding-change model of the mechanism of ATP-synthase. How and why is the proton-motive force used in the reaction cycle of ATP synthase

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter27: Metabolic Integration And Organ Specialization

Section: Chapter Questions

Problem 20P: Figure 27.3 illustrates the response of R (ATP-regenerating) and U (ATP-utilizing) enzymes to energy...

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ATP Synthase is known to catalyze the synthesis of ATP with a ΔG°’ close to zero, and a Keq' close to. Why is the value of ΔG°’ different from the known value which is 30.5 kJ/mol (the energy for the reverse of ATP hydrolysis)? If the Keq' value is close to one, how is it ensured that the reaction is driven to the product side and more ATP is obtained?
Coupled reactions occur where a nonspontaneous reaction is enabled by coupling it to a spontaneous reaction. This approach is common in biological settings. Determine if ATP could be generated by this biochemical reaction. You have calculated that cell potential is +0.637V. An example of a coupled reaction is the first step of glycolysis, the phosphorylation of glucose to form glucose-6-phosphate shown below. The net ∆Gº for this reaction is
A direct measurement of the standard free-energy change associated with the hydrolysis of ATP is technically demanding because the minute amount of ATP remaining at equilibrium is difficult to measure accurately. The value of ΔG′° can be calculated indirectly, however, from theequilibrium constants of two other enzymatic reactions having less favorable equilibrium constants:Using this information for equilibrium constants determined at 25 °C, calculate the standard free energy of hydrolysis of ATP.
Describe the conformational changes (including substrates that bind to the different conformations) that occur in the F1 domain of ATP Synthase that result from protons flowing through the Fo domain down their concentration gradient:
V-class proton pumps run backward relative to the F-class ATP synthase. Consider the cartoon, which shows the conformations of the beta-subunits and ATPIADP + Pj of the F-class synthase. Which of the following associations between the conformation of the beta subunit and ATP/ADP + P¡ is correct for V- Binding Change Mechanism loose binding ADP+P ATP ATP class pumps? C repeat ADP + P, ADP АТР tight binding АТР +P оpen АТР O The open conformation releases ATP. Hydrolysis of ATP to ADP + P¡ drives the change from tight to loose. O Binding of ADP + P¡ drives change from open to loose. Hydrolysis of ATP to ADP + Pj drives the change from open to loose.
Otto Warburg made an interesting observation in the 1930s about cancer cells using the fermentation pathway to catabolize pyruvate even when the oxygen supply seemed sufficient for oxidative phosphorylation. One modern explanation for this “Warburg Effect” is that it protects the cancer cells from damage from free radicals. Provide a biochemical rationale for this explanation.
In a biochemical pathway, three ATP molecules are hydrolyzed. The endergonic reactions in the pathway require a total of 17.3 kcal/mole of energy to drive the reactions of the pathway. What is the overall change in free energy of the biochemical pathway? Is the overall pathway endergonic or exergonic?
Back in 1962, Gerhart and Pardee developed a model for the regulation of the activity of the ATCase enzyme by CTP and ATP, using the pathway given in Figure 1. Describe that model, using information presented here as well as what you have learned about allosteric enzymes. Be sure to include a sentence explaining the physiological significance of your model.
The electron-transport chain consists of a number of multi protein complexes, which work in conjunction to pass electrons from an electron carrier, such as NADH, to O2. What is the role of these complexes in ATP synthesis? It has been demonstrated that respiration supercomplexes contain all the protein components necessary for respiration. Why is this beneficial for ATP synthesis, and what is one way that the existence of super complexes has been demonstrated experimentally? Coenzyme Q (CoQ) is not a protein, but a small, hydrophobic molecule. Why is it important for the functioning of the electron transport chain that CoQ is a hydrophobic molecule?
When enzyme solutions are heated, there is a progessive loss of catalytic activty over time due to denaturation of the enzyme. A solution of the enzyme hexokinase incubated at 45 degrees Celsius lost 50% of its activity in 12 minutes, but when incubated at 45 degrees Celsius in the presence of a very large concentration of one of its substrates, it lost only 3% of its activity in 12 minutes. Suggest why thermal denaturation of hexokinase was retarded in the presence of one substrates.
In working skeletal muscle under anaerobic conditions, glyceraldehyde 3-phosphate is converted to pyruvate (the payoff phase of glycolysis), and the pyruvate is reduced to lactate. Write balanced biochemical equations for all the reactions in this process, with the standard free-energy change for eachreaction. Then write the overall or net equation for the payoff phase of glycolysis (with lactate as the end product), including the net standard free-energy change.
The reaction catalyzed by citrate syn- thase, shown on the right, is the first step of the TCA cycle. In glycolysis, two key reactions to produce ATP occur because an unfavorable reaction is coupled to another reaction that is thermodynamically favorable. The reaction catalyzed by citrate synthase, shown on the right, is similarly coupled to an unfavorable reac- tion in the TCA cycle. Write the unfavorable reaction using structural formulas and write the key step that drives the two coupled reactions forward. What is the overall AG'o of the coupled reactions? CH3-C >=0 + S-COA Acetyl-CoA 0-C-COO- CH₂-COO Oxaloacetate H₂O COA-SH J citrate synthase CH₂-C HỌ—C—COO SO CH₂-COO Citrate AG'= -32.2 kJ/mol