Although phosphoesters are generally not energetic enough to donate the phosphate to make a high energy bond (e.g., a phosphoanhydride), the phosphate in PEP is used to convert ADP to ATP in the pyruvate kinase reaction. Carefully explain the ‘quirk’ of this reaction that makes it energetically feasible.

Although phosphoesters are generally not energetic enough to donate the phosphate to make a high energy bond (e.g., a phosphoanhydride), the phosphate in PEP is used to convert ADP to ATP in the pyruvate kinase reaction. Carefully explain the ‘quirk’ of this reaction that makes it energetically feasible.

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter23: Fatty Acid Catabolism

Section: Chapter Questions

Problem 21P: Using the ActiveModel for enoyl-CoA dehydratase, give an example of a case in which conserved...

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Which reaction below in the glycolytic pathway has a highly unfavorable delta Gº' but a favorable delta G under physiological conditions? 1,3-Bisphosphoglycerate + ADP3-Phosphoglycerate + ATP O2-phosphoglyerate → phosphoenolpyruvate Ofructose-1,6-bisphosphate dihydroxyacetone phosphate + glyceraldehyde-3-phosphate Ofructose-6-phosphate → fructose-1,6-bisphosphate
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.
Hexokinase catalyzes the first step of glycolysis, in which glucose is phosphorylated to form glucose‑6‑phosphate. Give two reasons why a Mg2+ cation is required to facilitate this reaction.
During glycogen synthesis, glucose-1P is converted into a molecule called UDPG. This reaction also cleaves uridine triphosphate (UTP) forming uridine monophosphate and pyrophosphate (PPi). Provide four reasons why UTP can be used to power this reaction (no diagrams necessary).
the first two reactions in glycolysis associated with unfavorable ∆G° values, i.e., ∆G° > 0, both produce a product with high phosphoryl group transfer potential. (ATP formation is not considered here.) Compare the two reactions and describe what the driving force is for both reactions that allows glycolysis to proceed to formation of pyruvate.
phosphofructokinase is an allosteric enzyme that catalyzes the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate and represents the key control point in mammalian glycolysis. The enzyme is a homotetramer that is inhibited by ATP binding, activated by AMP binding, negatively regulated by phosphorylation, and competitively inhibited by 2,5-anhydro-D-glucitol-1,6-diphosphate. (a) Would you expect a plot of the initial rate of fructose 1,6-bisphosphate formation as a function of substrate concentration to show a sigmoidal or hyperbolic curve? (b) How would each of the regulators above affect the dynamics of the T state to R state equilibrium of phosphofructokinase? Briefly explain your reasoning. (c) If it were possible to isolate phosphofructokinase monomers in an active form, how would you expect the kinetics in (a) to be affected? How would the rate of the reaction be affected by ATP, AMP, and 2,5-anhydro-D-glucitol-1,6-diphosphate? Briefly explain your answers.
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.
The phosphorylation and oxidative decarboxylation of oxaloacetate by inorganic phosphate (Pi) to make phosphoenolpyruvate and carbon dioxide is endergonic under intracellular conditions. It is characterized by this equation: Oxaloacetate + Pi ←→ Phosphoenolpyruvate + H2O + CO2 ΔG’ = +24.6 kJ/mol The synthesis of GTP from GDP and inorganic phosphate (Pi) in solution is endergonic under intracellular conditions, and it is characterized by this equation: GDP + Pi ←→ GTP + H2O ΔG’ = +30.5 kJ/mol Write a new net thermodynamically coupled reaction equation that describes the synthesis of phosphoenolpyruvate from oxaloacetate using the hydrolysis of GTP to power the reaction and calculate the new net ΔG’ of this reaction. Show all of your work.
The high phosphoryl transfer potential of 1,3-bisphosphoglycerate is explained by the resonance stability of the product, 3-phosphoglycerate. The same explanation applies to the reaction that generates resonance stabilized pyruvate from phosphoenolpyruvate. Show the resonance structures for both products, 3-phosphoglycerate and pyruvate, and state why the reactant in both reactions is not resonance stabilized.
Based on the action of thiamine pyrophosphate in catalysis of the pyruvate dehydrogenase reaction, suggest a suitable mechanism for the fourth step in the pyruvate decarboxylase reaction in yeast:
Imagine a triglyceride comprised of (3) saturated C12 fatty acids. Calculate the number of ATP generated from the complete oxidation of one of these 12-carbon fatty acids to CO2 and water in the liver. Assume that each NADH = 2.5 ATP and each FADH2 = ETC generates 1.5 ATP. Any step that yields pyrophosphate as a product should be treated as an input (i.e. net loss) of (2) ATP.
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