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 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.

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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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.
Identify the Krebs cycle enzyme that consumes a 3-carbon substrate molecule, producing a 2- carbon product molecule (attached to acetyl-CoA), along with NADH, and one molecule of CO2. succinyl CoA synthetase a-ketoglutarate dehydrogenase pyruvate dehydrogenase isocitrate dehydrogenase malate dehydrogenase
The pyruvate dehydrogenase complex catalyzes the oxidative decarboxylation of pyruvate to form acetyl‑CoA. E1E1 , E2E2 , and E3E3 are abbreviations for the enzymes of the complex. Classify the enzyme names, prosthetic groups, and reactions as E1E1 , E2E2 , or E3E3 .
Complete the following description of the mechanism of the pyruvate dehydrogenase complex by using words provided. Not all words will be used. Each word will be used only one time. 5 Three enzymes of the pyruvate dehydrogenase complex work together to catalyze the production of Acetyl CoA from Pyruvate. First, a 2-carbon unit composed of Carbons # Pyruvate are added to the co-enzyme and whereas Carbon # of leaves as CO» The C-2 unit together with the co-enzyme is called transferred to the 2nd co-enzyme 11 12 The C-2 unit is then which is initially in its state. The enzyme that catalyzes this step is From here, the C-2 unit is transferred to form a linkage with CoA-SH to generate Acetyl COA Oxidized Hydroxyethyl TPP Phosphodiester Reduced Hydroxypropiony! TPP Lipoamide E-1 NADH 3 Dihydrolipoyl dehydrogenase Thioester 2 HydroxyacetyITPp Dihydropipoyl Transacetylase Type the words in the correct order separated by commas. Example: 1, 3, E-1, Thioester, Lipoamide ...
Coenzyme A (CoA-SH) plays an important role in the Pyruvate Dehydrogenase Complex reaction. Which is correct? Coenzyme A serves as an electron acceptor in this reaction. The hydrolysis of a CoA thioester has a positive AG", the hydrolysis is endergonic and unfavorable. Coenzyme A is derived from thiamine, a vitamin. Coenzyme A contains -SH group and can serve as an acyl group carrier.
The diagram on the right compares the O2 uptake activity of mitochondria isolated from cultures of (wt) STHdhQ7/Q7 and mutant STHDHQ111/Q111 striatal neuronal progenitor cells, as introduced in Question 1. Panels A and B be- long to wt mitochondria and Panels C and D be- long to HD mitochondria. The isotonic medium was buffered to pH 7.4 with inorganic phosphate. Respiration is supported initially by addition of py- ruvate (+ malate) at t = 0, followed by additions of ADP (sufficient to consume all of the O2 in the incubation medium), R (rotenone), S (succinate), and O (oligomycin). For Panels A and C, Ca2+ had been added to a concentration of 0.9 µM, Ca2+ 2. B A WT 400 ADP ADP 450 300 - 300 200 Ca2 10 uM 150 100 - C HD 400 ADP R ADP R SO 450 300 - V s Ca2 10 uM 300 200 - 150 100 - while for mitochondria in Panels B and D, had been added to the medium to a final concen- Time 20 min tration of 10 µM, sufficient to require translocation into the mitochondrial matrix by the Ca2+…
Each of the following enzymes are similar in that they are all regulation points for the pathway/cycle they operate in ... except for one enzyme. Which of the following is not a regulated enzyme? Pyruvate carboxylase Transketolase Glycogen phosphorylase Citrate Synthase Phosphofructokinase Acetyl CoA carboxylase 888888
The synthesis of the activated form of acetate (acetyl-CoA) is carried out in an ATP-dependent process: Acetate + CoA + ATP → acetyl-CoA + AMP + PPi (a) The ∆G’o for the hydrolysis of acetyl-CoA to acetate and CoA is - 32.2 kJ/mol and that for hydrolysis of ATP to AMP and PPi is - 30.5 kJ/mol. Calculate ∆G’o for the ATP-dependent synthesis of acetyl-CoA. (b) Almost all cells contain the enzyme inorganic pyrophosphatase, which catalyzes the hydrolysis of PPi to Pi. What effect does the presence of this enzyme have on the synthesis of acetyl-CoA? Explain.
The mechanism for the conversion from alpha kytoglutarate into succinyl CoA by alpha-ketoglutare dehydrogenase is analogous to the pyruvate dehydrogenase mechanism. Draw and show the major intermediates and arrow pushing for the enzyme-catalyze process for the conversion of alpha-ketoglutarate to succinyl CoA. Note: the carbanion of thiamine pyrophosphate nucleophillically attacks C-2 of the alpha-ketoglutarate, i.e., the carbonyl carbon of that substrate.
The same E1-Ez-E3 multienzyme structure found in the pyruvate dehydro- genase and the a-ketoglutarate dehydrogenase complexes is also used in the branched-chain a-ketoacid dehydrogenase complex, which participates in the catabolism of branched chain amino acids. Draw the reaction product when the following substrate is acted on by the branched chain a-keto acid dehydrogenase complex. H,C -C-COo- H,C
The citric acid cycle is a critical sequence of reactions for energy production, which take place in the matrix of the mitochondria. The reaction cycle requires materials from the cytosol to be converted into acetyl CoA, which represents the starting point of a new cycle. Which of the following statements about acetyl CoA is true? (a) Acetyl CoA is recycled at the end of every cycle. (b) Oxaloacetate is attached to acetyl CoA to feed the citric acid cycle. (c) Triacylglycerol molecules are transported into the mitochondrial matrix and cleaved by lipases to produce acetyl CoA. (d) Oxaloacetate is converted directly into acetyl CoA to feed the citric acid cycle
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