. Briefly describe the biological rationale for cach of the following allosteric phenomena: (a) activation of pyruvate carboxylase by acetyl-CoA; (b) acti- vation of pyruvate dehydrogenase kinase by NADH; (c) inhibition of isoci- trate dehydrogenase by NADH; (d) activation of isocitrate dehydrogenase by ADP; (e) inhibition of a-ketoglutarate dehydrogenase by succinyl-CoA; (f) activation of pyruvate dehydrogenase phosphatase by Ca*.

. Briefly describe the biological rationale for cach of the following allosteric phenomena: (a) activation of pyruvate carboxylase by acetyl-CoA; (b) acti- vation of pyruvate dehydrogenase kinase by NADH; (c) inhibition of isoci- trate dehydrogenase by NADH; (d) activation of isocitrate dehydrogenase by ADP; (e) inhibition of a-ketoglutarate dehydrogenase by succinyl-CoA; (f) activation of pyruvate dehydrogenase phosphatase by Ca*.

Biochemistry

6th Edition

ISBN:9781305577206

Author:Reginald H. Garrett, Charles M. Grisham

Publisher:Reginald H. Garrett, Charles M. Grisham

Chapter19: The Tricarboxylic Acid Cycle

Section: Chapter Questions

Problem 22P: Study Figure 19.18 and decide which of the following statements is false. Pyruvate dehydrogenase is...

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Ethanol as a Source of Metabolic Energy (Integrates with Chapters 19 and 20.) Acetate produced in ethanol metabolism can be transformed into acetyl-COA by the acetyl thiokinase reaction: Acetate+ATP+CoASHacetyleCoA+AMP+PPiAcetyle-CoA then can enter the citric acid cycle and undergo oxidation to 2 CO2by this route, assuming oxidative phosphorylation is part of the process? (Assume all reactions prior to acetyl-CoA entering the citric acid cycle occur outside the mitochondrion). Per carbon atom, which is a better metabolic fuel, ethanol or glucose? That is, how many ATP equivalents per carbon atom are generated by combustion of glucose versus ethanol to CO2?
Study Figure 19.18 and decide which of the following statements is false. Pyruvate dehydrogenase is inhibited byÂ· NIADH. Pyruvate dehydrogenase is inhibited by AÎ¤Î¡. Citrate synthase is inhibited by NADH. Succinyl-CoA activates citrate synthase. Acetyl-CoA activates pyruvate carboxylase.
Briefly describe the biological rationale for each of the following allosteric phenomena: (a) activation of pyruvate carboxylase by acetyl-CoA; (b) activation of pyruvate dehydrogenase kinase by NADH; (c) inhibition of isocitrate dehydrogenase by NADH; (d) activation of isocitrate dehydrogenase by ADP; (e) inhibition of a-ketoglutarate dehydrogenase by succinyl-CoA; (f) activation of pyruvate dehydrogenase phosphatase by Ca2+.
Briefly describe the biological rationale for each of the following allosteric phenomena: (a) activation of pyruvate carboxylase by acetyl-CoA; (b) activation of pyruvate dehydrogenase kinase by NADH; (c) inhibition of isocitrate dehydrogenase by NADH; (d) activation of isocitrate dehydrogenase by ADP; (e) inhibition of α-ketoglutarate dehydrogenase by succinyl-CoA; (f) activation of pyruvate dehydrogenase phosphatase by Ca2 +.
The pyruvate dehydrogenase (PDH) complex catalyzes the oxidative decarboxylation of pyruvate to acetyl‑CoA and CO2.CO2. Multiple copies of pyruvate dehydrogenase (E1), dihydrolipoyl transacetylase (E2), and dihydrolipoyl dehydrogenase (E3) along with five cofactors form the PDH complex. Biochemists have studied the PDH complex for decades, in part due to its interesting use of substrate channeling during catalysis. What is the benefit of substrate channeling? A. Intermediates of a multistep reaction sequence do not dissociate from the enzyme complex. B. Every intermediate or product made by the PDH complex enters the citric acid cycle as a substrate. C. The PDH complex sequesters excess substrate to use at later time. D. Reaction progress is not limited by the diffusion constant. E.The PDH active site forms in the hydrophobic core of the complex instead of a surface‑exposed region.
The pyruvate dehydrogenase (PDH) complex catalyzes the oxidative decarboxylation of pyruvate to acetyl‑CoA and CO2.CO2. Multiple copies of pyruvate dehydrogenase (E1), dihydrolipoyl transacetylase (E2), and dihydrolipoyl dehydrogenase (E3) along with five cofactors form the PDH complex. Biochemists have studied the PDH complex for decades, in part due to its interesting use of substrate channeling during catalysis. What is the molecular mechanism of substrate channeling in the PDH complex? A. The swinging lipoyllysyl arm of E2 carries electrons and an acetyl group from E1 to E2. B.The active sites of E1, E2, and E3 undergo conformational changes that move products of one reaction to their next position without solvent exposure. C.Electrons and an acetyl group travel between E1 and E2 through a tunnel in E2. D. Metal ions coordinated with thiamine pyrophosphate (TPP) in E1 shield the electrons and acetyl group from scavenging by other enzymes until they reach E3.
Discuss the metabolic control for HMG CoA reductase synthesis and activity
For the pyruvate dehydrogenase complex, please identify the oxidation states of every atom and prove whether the reaction is oxidized or not Pyruvate --> Hydroxyethyl TPP B. Hydroexythl TPP --> Acetyl Lipoylysine C. Acetyl Lipoylysine --> Acetyl-CoA
Describe the common characteristic among the reactions catalyzed by pyruvate dehydrogenase (PDH), isocitrate dehydrogenase (ID), and alpha-ketoglutarate dehydrogenase (KD) based on reversibility.
The oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate by glyceraldehyde 3-phosphate dehydrogenase has an unfavourable equilibrium constant (K'eq= 0.08; G′° = 6.3 kJ/mol), yet the flow at this point in the glycolytic pathway is smooth. How does the cell get out of the unfavourable equilibrium?
The oxidation of glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate, catalyzed by glyceraldehyde 3- phosphate dehydrogenase, proceeds with an unfavorable equilibrium constant ( K'eq= 0.08; ΔG′° = 6.3 kJ/mol), yet the flow through this point in the glycolytic pathway proceeds smoothly. How does the cell overcome the unfavorable equilibrium?
Draw a plausible mechanism for the oxidation of dihydrolipoamide to lipoamide by the E3 subunit (dihydrolipoamide dehydrogenase) of pyruvate dehydrogenase complex.