TCA
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Questions and Answers

What are the main products generated from one acetyl-CoA entering the TCA cycle?

  • 2 FADH2, 10 H+, and 2 CO2
  • 3 CO2, 2 NADH, and ADP
  • 6 CO2, 10 NADH, and 4 ATP
  • 2 CO2, 3 NADH, FADH2, CoASH, and ATP (correct)

    • In the complete oxidation of acetate, what role do electron carriers play?

  • They convert NAD+ into glucose.
  • They directly produce ATP without the need for further reactions.
  • They substitute the need for glucose metabolism.
  • They help conserve free energy by transporting electrons. (correct)

    • What effect does glycolysis have on the TCA cycle?

  • It decreases the overall energy yield of cellular respiration.
  • It generates pyruvate which is converted to acetyl-CoA for entry into the TCA cycle. (correct)
  • It eliminates the need for the TCA cycle.
  • It produces oxygen required for the TCA cycle.

    • During the complete oxidation of glucose through glycolysis and the TCA cycle, how many CO2 molecules are produced?

    <p>6 CO2</p> Signup and view all the answers

    Why is the oxidation of acetyl-CoA to CO2 significant in metabolism?

    <p>It releases energy that is stored in the form of ATP and electron carriers.</p> Signup and view all the answers

    What is the role of pyruvate dehydrogenase (E1) in the reaction?

    <p>It catalyzes the conversion of pyruvate to acetyl CoA.</p> Signup and view all the answers

    Which molecule participates first in the nucleophilic attack in the pyruvate dehydrogenase reaction?

    <p>Hydroxyethyl TPP</p> Signup and view all the answers

    What by-product is formed upon the departure of CO2 during the reaction?

    <p>Hydroxyethyl TPP</p> Signup and view all the answers

    What happens to TPP after the transfer of the hydroxyethyl group?

    <p>It is eliminated.</p> Signup and view all the answers

    Which compound is formed when the hydroxyethyl group is added to the lipoamide moiety?

    <p>Hydroxyethyl lipoamide</p> Signup and view all the answers

    What is the final product transferred to CoA in this reaction sequence?

    <p>Acetyl group</p> Signup and view all the answers

    During which step is the hydroxyethyl carbanion generated?

    <p>Nucleophilic attack</p> Signup and view all the answers

    What is the final role of dihydrolipoamide in the reaction sequence?

    <p>It captures the acetyl group.</p> Signup and view all the answers

    What spectral peak is observed when NAD+ is reduced to NADH?

    <p>340 nm</p> Signup and view all the answers

    What is the primary reason the Krebs cycle is referred to as the Tricarboxylic Acid (TCA) cycle?

    <p>It contains three carboxylic acid groups in citrate and isocitrate.</p> Signup and view all the answers

    Which enzyme of the TCA cycle is membrane-bound and what cofactor does it utilize?

    <p>Succinate dehydrogenase, FAD</p> Signup and view all the answers

    How many enzymes in the TCA cycle function far from equilibrium under physiological conditions?

    <p>3</p> Signup and view all the answers

    What is the primary function of the keto group in the decarboxylation process?

    <p>To act as an electron sink</p> Signup and view all the answers

    Which coenzyme is involved in the mechanism of the α-ketoglutarate dehydrogenase?

    <p>TPP</p> Signup and view all the answers

    Which of the following statements about the TCA cycle is incorrect?

    <p>It generates ATP directly in each cycle.</p> Signup and view all the answers

    What is produced alongside NADH during the oxidative decarboxylation of α-keto acids?

    <p>Succinyl-CoA</p> Signup and view all the answers

    Which enzyme is NOT part of the multienzyme complex involved in α-ketoglutarate dehydrogenase?

    <p>Pyruvate kinase (E4)</p> Signup and view all the answers

    How does Mn2+ interact with the carbonyl group during the dehydrogenase reaction?

    <p>It coordinates to polarize the electronic charge</p> Signup and view all the answers

    What effect does the oxidative decarboxylation have on cellular metabolism?

    <p>It increases the production of NADH and succinyl-CoA</p> Signup and view all the answers

    What pathway can NADH from the dehydrogenase reaction follow?

    <p>It can be routed through the electron transport chain</p> Signup and view all the answers

    What distinguishes the α-ketoglutarate dehydrogenase reaction from others in the citric acid cycle?

    <p>It involves a decarboxylation step releasing CO2</p> Signup and view all the answers

    What inhibits the activity of the pyruvate dehydrogenase complex (PDC)?

    <p>Acetyl-CoA and NADH</p> Signup and view all the answers

    Which of the following is an anaplerotic pathway for the TCA cycle?

    <p>Pyruvate carboxylase</p> Signup and view all the answers

    Through which compound do valine and isoleucine enter the TCA cycle?

    <p>Succinyl-CoA</p> Signup and view all the answers

    What is the DGo' value for the hydrolysis of the thioester bond of Acetyl-CoA?

    <p>-31.5 KJ/mol</p> Signup and view all the answers

    Which metabolic process is primarily responsible for generating precursor molecules for the TCA cycle?

    <p>Transamination</p> Signup and view all the answers

    Which two compounds are generated as intermediates in the TCA cycle through transamination?

    <p>Oxaloacetate and α-ketoglutarate</p> Signup and view all the answers

    Which compound is formed from the reversible conversion of glutamate in many tissues?

    <p>α-Ketoglutarate</p> Signup and view all the answers

    What platform does odd-chain fatty acid oxidation primarily feed into the TCA cycle?

    <p>Succinyl-CoA</p> Signup and view all the answers

    What is the primary function of FAD in the oxidation of alkanes?

    <p>To oxidize alkanes to alkenes</p> Signup and view all the answers

    Which molecule is oxidized by NAD+ during the metabolic processes described?

    <p>Alcohols</p> Signup and view all the answers

    What does FADH2 reduce in the electron transport chain?

    <p>Coenzyme Q</p> Signup and view all the answers

    Which enzyme is described as the only membrane-bound TCA cycle enzyme?

    <p>Succinate dehydrogenase</p> Signup and view all the answers

    What is the outcome when succinate is oxidized in the presence of FAD?

    <p>FADH2 is produced</p> Signup and view all the answers

    What type of reaction characterizes the process involving succinate and FAD?

    <p>Redox reaction</p> Signup and view all the answers

    What role does CoA-SH play in the context of succinate dehydrogenase?

    <p>It is involved in the citric acid cycle</p> Signup and view all the answers

    What is generated alongside NADH during the oxidation of succinate?

    <p>GTP</p> Signup and view all the answers

    What does the oxidation of an alkane to an alkene achieve in terms of energy change?

    <p>It is an exergonic process</p> Signup and view all the answers

    What is the fate of electrons during the oxidation of succinate?

    <p>They are transferred to FAD</p> Signup and view all the answers

    Study Notes

    Tricarboxylic Acid (TCA) Cycle

    • The TCA cycle, also known as the Krebs cycle or citric acid cycle, is a crucial metabolic pathway.

    • It's a central part of cellular respiration, oxidizing acetyl-CoA to carbon dioxide.

    • The cycle involves eight steps, each catalyzed by a specific enzyme.

    • Acetyl-CoA enters the cycle by combining with oxaloacetate, forming citrate.

    • The seven subsequent steps decompose citrate back to oxaloacetate, creating a cyclical process.

    • NADH and FADH2 are produced during the cycle, crucial for electron transport.

    • The cycle relays electrons extracted from food to the electron transport chain.

    • The cycle provides a way to cleave a two-carbon compound such as acetate to carbon dioxide.

    • A common type of C-C cleavage is a-cleavage.

    • Neither cleavage strategies are suitable for acetate. Instead, living things use the clever chemistry of condensing acetate to oxaloacetate and undergoing a B-cleavage.

    • The TCA cycle combines this B-cleavage reaction with oxidation to form CO2, regenerate oxaloacetate, and capture the liberated metabolic energy in NADH and ATP.

    • Important intermediates for biosynthetic processes are produced by the Citric Acid Cycle including carbohydrates, amino acids, lipids and other molecules such as porphyrins.

    • Pyruvate carboxylase and glutamate are two major anaplerotic pathways.

    • The pyruvate dehydrogenase complex links glycolysis to the TCA cycle.

    • The Pyruvate Dehydrogenase Multienzyme Complex (PDC) is a cluster of three enzymes catalyzing the conversion of pyruvate to acetyl-CoA.

    • PDC requires five cofactors including thiamine pyrophosphate (TPP), lipoic acid, coenzyme A, flavin adenine dinucleotide (FAD), and NAD+.

    • The reaction occurs in the mitochondrial matrix.

    • The dihydrolipoyl transacetylase is the core of the complex.

    • The 24 subunits of the E₂ form a particle having cubic symmetry.

    • The 24 pyruvate dehydrogenase subunits form dimers and associate with the E₂ core at the centers of the 12 edges.

    • The 12 dihydrolipoyl dehydrogenase form dimers and attach to the E2 cube at the centers of the 6 faces.

    • The coenzymes and prosthetic groups for the PDC include thiamine pyrophosphate (TPP), lipoic acid, coenzyme A (CoA), flavin adenine dinucleotide (FAD), and nicotinamide adenine dinucleotide (NAD+).

    • In the TCA cycle, carbons come from acetyl-CoA and are oxidized to CO2, the cycle regenerates oxaloacetate, and captures energy in NADH and ATP.

    • Key enzymes and their roles in the TCA cycle are detailed (including their enzyme-bound cofactors & the reactions they catalyze).

    • The regulation of the TCA cycle includes product inhibition (e.g., citrate inhibits citrate synthase) and control by ADP, NADH and Ca2+.

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    Lecture 3- TCA Cycle PDF

    Description

    Explore the Tricarboxylic Acid (TCA) Cycle, a vital metabolic pathway known for its role in cellular respiration. This quiz covers the cycle's eight steps, enzyme interactions, and the production of NADH and FADH2. Understand how acetyl-CoA transforms into carbon dioxide through this intricate process.

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