Lecture 20

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Questions and Answers

Where does the citric acid cycle occur in eukaryotes?

  • Mitochondrial inner membrane
  • Plasma membrane
  • Cytoplasm
  • Mitochondrial matrix (correct)

Which of the following leads to the production of Acetyl CoA?

  • Glycolysis
  • Oxidative phosphorylation
  • Electron Transport Chain (ETC)
  • Fatty acid oxidation (correct)

What is the main role of the pyruvate dehydrogenase complex (PDH) in cellular respiration?

  • Production of ATP
  • Formation of NAD+
  • Reduction of Acetyl CoA
  • Conversion of pyruvate to Acetyl CoA (correct)

In which stage of cellular respiration does the conversion of pyruvate to Acetyl CoA occur?

<p>Stage 1: Production of Acetyl-CoA (C)</p> Signup and view all the answers

Which statement about the respiratory chain in oxidative phosphorylation is correct?

<p>It ultimately reduces O2 to H2O (C)</p> Signup and view all the answers

What drives the production of ATP in oxidative phosphorylation?

<p>Electron flow through the respiratory chain (B)</p> Signup and view all the answers

What is responsible for the reduction of the alkane to alkene in the Electron Transport Chain?

<p>FADH2 (A)</p> Signup and view all the answers

Which enzyme catalyzes the hydration of fumarate to malate?

<p>Fumarase (D)</p> Signup and view all the answers

What type of bond does fumarase always create during the hydration of fumarate to malate?

<p>L-sugars (D)</p> Signup and view all the answers

Which of the following is NOT a reason why intermediates react quickly in the Citrate Synthase and Malate DHase metabolon?

<p>They are protected from cellular degradation pathways (C)</p> Signup and view all the answers

Which of the following statements about the citric acid cycle is NOT true?

<p>It has a net gain of carbon atoms (C)</p> Signup and view all the answers

In which step(s) of the citric acid cycle is energy conserved by electron transfer to FAD or NAD+, forming FADH2 or NADH + H+?

<p>Steps 3, 4, and 6 (A)</p> Signup and view all the answers

Which of the following statements about the reversibility of steps in the citric acid cycle is true?

<p>Steps 1, 3, and 4 are irreversible, while all other steps are reversible (C)</p> Signup and view all the answers

Which of the following statements about the product of step 5 in the citric acid cycle is true?

<p>The product may be either ATP or GTP, depending on the isozyme catalyst (D)</p> Signup and view all the answers

What is the main similarity between the reaction converting α-ketoglutarate to succinyl-CoA and the pyruvate dehydrogenase reaction?

<p>Both reactions result in the generation of NADH. (B)</p> Signup and view all the answers

Which complex is similar in structure and function to the pyruvate dehydrogenase complex?

<p>α-Ketoglutarate dehydrogenase complex (C)</p> Signup and view all the answers

What is a key feature of the oxidative decarboxylation process catalyzed by the α-Ketoglutarate dehydrogenase complex?

<p>Net full oxidation of all carbons of glucose (D)</p> Signup and view all the answers

Which statement accurately describes succinyl-CoA?

<p>It is a higher-energy thioester bond. (A)</p> Signup and view all the answers

What role does product inhibition play in the regulation of the α-Ketoglutarate dehydrogenase complex?

<p>Stops the enzyme activity when enough product is formed (B)</p> Signup and view all the answers

What is the purpose of the oxidative decarboxylation reaction catalyzed by isocitrate dehydrogenase?

<p>To generate NADH and remove a carbon as CO2 from the citric acid cycle (A)</p> Signup and view all the answers

What is the purpose of the aconitase enzyme in the citric acid cycle?

<p>Aconitase catalyzes the conversion of citrate to cis-aconitate, which is then converted to isocitrate (B)</p> Signup and view all the answers

Which statement is true about the carbon atoms lost as CO2 during the oxidative decarboxylation of isocitrate?

<p>The carbon atoms lost as CO2 come from the breakdown of isocitrate, not from the acetyl-CoA or pyruvate (D)</p> Signup and view all the answers

What is the primary function of the lipoyl-lysine residue in the pyruvate dehydrogenase complex (PDC)?

<p>To act as a carrier of both hydrogen and an acetyl group (B)</p> Signup and view all the answers

Which of the following statements accurately describes the role of the lipoyl-lysine residue in the transfer of the acetyl group to coenzyme A?

<p>The lipoyl-lysine residue accepts the acetyl group from TPP and transfers it to dihydrolipoyl transacetylase (E2) (D)</p> Signup and view all the answers

Which of the following statements accurately describes the role of the lipoyl-lysine residue in the oxidation-reduction reactions of the pyruvate dehydrogenase complex?

<p>The lipoyl-lysine residue cycles between oxidized (disulfide) and reduced (dithiol) forms, facilitating the transfer of electrons (C)</p> Signup and view all the answers

What is the purpose of the long, flexible arms formed by cofactors like lipoate, biotin, and the combination of β-mercaptoethylamine and pantothenate?

<p>To act as tethers that move intermediates from one active site to the next (A)</p> Signup and view all the answers

How does the lipoyllysyl moiety contribute to the pyruvate dehydrogenase complex?

<p>Participating in the transfer of active aldehyde groups (C)</p> Signup and view all the answers

In the pyruvate decarboxylation process, what is the role of the dihydrolipoyl transacetylase enzyme?

<p>Facilitating the formation of acetyl CoA (B)</p> Signup and view all the answers

What is the significance of the oxidized form of the lipoyl residue in accepting the acetyl group?

<p>Enables the oxidation of the active aldehyde group (B)</p> Signup and view all the answers

How does the lipoyl group act as a carrier during the pyruvate decarboxylation process?

<p>Transfers hydrogen and an acetyl group simultaneously (C)</p> Signup and view all the answers

What is the primary role of the lipoyl-lysine residue in the pyruvate dehydrogenase complex (PDC)?

<p>To accept the acetyl group from the oxidative decarboxylation of pyruvate and transfer it to coenzyme A. (A)</p> Signup and view all the answers

What is the role of FAD in the reoxidation of the lipoamide cofactor in the pyruvate dehydrogenase complex?

<p>FAD acts as an electron acceptor, becoming reduced to FADH2 as the reduced lipoamide is reoxidized. (B)</p> Signup and view all the answers

What is the primary role of the dihydrolipoyl dehydrogenase (E3) enzyme in the pyruvate dehydrogenase complex?

<p>To reoxidize the reduced lipoamide cofactor by transferring electrons to FAD, which is then reoxidized by NAD+. (A)</p> Signup and view all the answers

What is the role of thiamine pyrophosphate (TPP) in the pyruvate dehydrogenase complex?

<p>TPP catalyzes the decarboxylation of pyruvate, forming the acetyl group that is then transferred to the lipoyl-lysine residue. (C)</p> Signup and view all the answers

What is the primary role of the dihydrolipoyl transacetylase (E2) enzyme in the pyruvate dehydrogenase complex?

<p>To transfer the acetyl group from the lipoyl-lysine residue to coenzyme A, forming acetyl-CoA. (C)</p> Signup and view all the answers

In the pyruvate dehydrogenase complex, which enzyme is responsible for the decarboxylation of pyruvate?

<p>Pyruvate dehydrogenase (E1) (A)</p> Signup and view all the answers

What is the role of the lipoyl-lysine residue in the pyruvate dehydrogenase complex?

<p>It transfers the acetyl group from TPP to coenzyme A. (A)</p> Signup and view all the answers

What is the function of dihydrolipoyl dehydrogenase (E3) in the pyruvate dehydrogenase complex?

<p>It oxidizes the reduced lipoyl groups of E2 using NAD+. (D)</p> Signup and view all the answers

What is the role of thiamine pyrophosphate (TPP) in the pyruvate dehydrogenase complex?

<p>It acts as a cofactor for the decarboxylation of pyruvate. (A)</p> Signup and view all the answers

Which enzyme in the pyruvate dehydrogenase complex catalyzes the transfer of the acetyl group from the lipoyl-lysine residue to coenzyme A?

<p>Dihydrolipoyl transacetylase (E2) (B)</p> Signup and view all the answers

What is the primary role of the dihydrolipoyl dehydrogenase (E3) enzyme in the pyruvate dehydrogenase complex?

<p>To reoxidize the reduced lipoamide cofactor using NAD+ as the electron acceptor (B)</p> Signup and view all the answers

What is the primary function of the lipoyl-lysine residue in the pyruvate dehydrogenase complex (PDC)?

<p>To act as a flexible arm that shuttles the acetyl group from the pyruvate dehydrogenase (E1) enzyme to the dihydrolipoyl acetyltransferase (E2) enzyme (B)</p> Signup and view all the answers

What is the role of thiamine pyrophosphate (TPP) in the pyruvate dehydrogenase complex?

<p>To remove a carbon in the form of CO2 and create a 2-carbon acetyl group during the decarboxylation of pyruvate (B)</p> Signup and view all the answers

What is the main similarity between the reaction converting α-ketoglutarate to succinyl-CoA and the pyruvate dehydrogenase reaction?

<p>Both reactions involve the removal of a carboxyl group as CO2 (C)</p> Signup and view all the answers

What is the role of the lipoyl-lysine residue in the transfer of the acetyl group to Coenzyme A?

<p>The lipoyl-lysine residue acts as a flexible arm that shuttles the acetyl group from the pyruvate dehydrogenase (E1) enzyme to the dihydrolipoyl acetyltransferase (E2) enzyme (A)</p> Signup and view all the answers

What is the primary role of the dihydrolipoamide acetyltransferase (E2) enzyme in the pyruvate dehydrogenase complex?

<p>To transfer the acetyl group from the lipoyl-lysine residue to coenzyme A (A)</p> Signup and view all the answers

How does the lipoyl-lysine residue contribute to the function of the pyruvate dehydrogenase complex?

<p>The lipoyl-lysine residue serves as a flexible arm that shuttles the acetyl group between the enzymes in the complex (C)</p> Signup and view all the answers

What is the primary role of the pyruvate dehydrogenase complex (PDC) in cellular respiration?

<p>Conversion of pyruvate to acetyl-CoA (C)</p> Signup and view all the answers

Which of the following statements accurately describes the regulation of the pyruvate dehydrogenase complex (PDC)?

<p>PDH phosphatase stimulates the complex by removing the phosphate group (C)</p> Signup and view all the answers

What is the primary role of the lipoyl-lysine residue in the pyruvate dehydrogenase complex (PDC)?

<p>To transfer the acetyl group from pyruvate to coenzyme A (A)</p> Signup and view all the answers

Which enzyme in the pyruvate dehydrogenase complex catalyzes the transfer of the acetyl group from the lipoyl-lysine residue to coenzyme A?

<p>Dihydrolipoyl transacetylase (E2) (C)</p> Signup and view all the answers

What is the primary function of the dihydrolipoyl dehydrogenase (E3) enzyme in the pyruvate dehydrogenase complex?

<p>To reoxidize the lipoamide cofactor using FAD (B)</p> Signup and view all the answers

Which of the following statements accurately describes the role of the lipoyl-lysine residue in the transfer of the acetyl group to coenzyme A?

<p>The lipoyl-lysine residue first transfers the acetyl group to dihydrolipoyl transacetylase (E2), which then transfers it to coenzyme A (C)</p> Signup and view all the answers

How is the pyruvate dehydrogenase complex regulated?

<p>Through phosphorylation by PDH kinase (C)</p> Signup and view all the answers

Pyruvate is converted into which compound by the pyruvate dehydrogenase complex, as stated in the text?

<p>Acetyl CoA (A)</p> Signup and view all the answers

What role does PDH kinase play in relation to the pyruvate dehydrogenase complex based on the text?

<p>Inhibiting the complex by phosphorylation (B)</p> Signup and view all the answers

What molecules are generated for each cycle involving two pyruvate molecules in the pyruvate dehydrogenase complex?

<p>2 CO2, 2 acetyl coa, 2 FADH2, and 2 NADH (B)</p> Signup and view all the answers

What is the role of pyruvate dehydrogenase kinase in the regulation of the pyruvate dehydrogenase complex?

<p>Inhibits enzyme activity (C)</p> Signup and view all the answers

Which molecules can influence the activity of the pyruvate dehydrogenase complex, other than ATP and NADH?

<p>Calcium ions and insulin (A)</p> Signup and view all the answers

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