Acetyl Coa & Tca Cycle

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| By Iyanna Peppers
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Iyanna Peppers
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  • 1/14 Questions

    Pyruvate dehydrogenase complex catalyzes the:

    • Oxidative decarboxylation of pyruvate to CO2 and acetyl CoA
    • Citrate to isocitrate reaction
    • Addition of a carboxylic acid to pyruvate, forming oxaloacetate
    • Formation of fumarate and FADH2 from succinate
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About This Quiz

This quiz on 'Acetyl CoA & TCA Cycle' evaluates understanding of key biochemical reactions, including the role of pyruvate dehydrogenase and the production of NADH. It tests knowledge on enzyme subunits, cofactors, and their vitamin derivatives, crucial for students and professionals in biochemistry.

Acetyl Coa & Tca Cycle - Quiz

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  • 2. 

    Catabolic action yields:

    • High energy metabolites

    • New material (ie, amino acids, porphyrins)

    Correct Answer
    A. High energy metabolites
    Explanation
    Catabolic action refers to the breakdown of complex molecules into simpler ones. This process releases energy, which is stored in high energy metabolites. These metabolites, such as ATP, can be used by the cell for various energy-requiring processes. Additionally, catabolic action also produces new materials like amino acids and porphyrins, which can be used for the synthesis of proteins and other essential molecules in the cell.

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  • 3. 

    ____ and _____ inhibit key steps of the TCA cycle.

    • ATP; NADH

    • NAD+; ADP

    • Succinyl CoA; ADP

    • ATP: NAD+

    Correct Answer
    A. ATP; NADH
    Explanation
    ATP and NADH inhibit key steps of the TCA cycle. ATP is a high-energy molecule that is produced during cellular respiration and is used as a source of energy for various cellular processes. When ATP levels are high, it indicates that the cell has sufficient energy and can inhibit the TCA cycle to prevent excessive production of ATP. NADH, on the other hand, is an electron carrier molecule that is generated during the breakdown of glucose. High levels of NADH indicate that the cell has sufficient energy and can also inhibit the TCA cycle to prevent excessive production of NADH.

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  • 4. 

    ______ is complex II of the mitochondrial electron transport chain.

    • Succinate dehydrogenase

    • Malate dehydrogenase

    • α-ketoglutarate dehydrogenase

    • Aconitase

    Correct Answer
    A. Succinate dehydrogenase
    Explanation
    Succinate dehydrogenase is complex II of the mitochondrial electron transport chain. It is responsible for transferring electrons from succinate to ubiquinone, which is a crucial step in the production of ATP. This enzyme is embedded in the inner mitochondrial membrane and plays a key role in the oxidation of succinate, a substrate derived from the citric acid cycle.

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  • 5. 

    1 mole of pyruvate to acetyl-CoA yields ___ mole(s) of NADH.

    • 1

    • 2

    • 4

    • 3

    Correct Answer
    A. 1
    Explanation
    When 1 mole of pyruvate is converted into acetyl-CoA, it produces 1 mole of NADH. This is because during the conversion process, one molecule of NAD+ is reduced to NADH. Therefore, the correct answer is 1.

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  • 6. 

    Molecules with ____, such as dihydrolipoamide, are targets for covalent modification by arsenite.

    • Proximal thiols

    • Distal thiols

    • Proximal hydroxyls

    • Distal hydroxyls

    Correct Answer
    A. Proximal thiols
    Explanation
    Molecules with proximal thiols, such as dihydrolipoamide, are targets for covalent modification by arsenite. This means that arsenite can form a covalent bond with the proximal thiols in dihydrolipoamide, leading to a chemical modification of the molecule. Proximal thiols are sulfur-containing groups that are located close to the active site of the molecule, making them susceptible to interaction with arsenite. This interaction can have various effects on the function and structure of the molecule, potentially leading to biological consequences.

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  • 7. 

    The TCA cycle is considered to be anapleurotic. This describes:

    • That there are multiple points around the cycle where reactants feed in.

    • The circular, regenerative nature of the TCA cycle.

    • That malate is the only TCA cycle product that can be shunted through the mitochondrial membrane.

    • That the TCA cycle is reversible when needed.

    Correct Answer
    A. That there are multiple points around the cycle where reactants feed in.
    Explanation
    The TCA cycle is considered to be anapleurotic because there are multiple points around the cycle where reactants can enter. This means that the cycle can be replenished with intermediates from other metabolic pathways, ensuring a constant supply of reactants for energy production. This flexibility allows the TCA cycle to adapt to changing metabolic demands and maintain its function as a central hub in cellular metabolism.

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  • 8. 

    Which pyruvate dehydrogenase cofactors are acyl group carriers?

    • Coenzyme A

    • Lipoamide

    • FAD

    • NAD+

    • TPP

    Correct Answer(s)
    A. Coenzyme A
    A. Lipoamide
    Explanation
    Coenzyme A and lipoamide are the acyl group carriers in the pyruvate dehydrogenase complex. Coenzyme A carries the acetyl group, while lipoamide carries the other acyl groups, such as the succinyl and propionyl groups. FAD and NAD+ are electron carriers, and TPP (thiamine pyrophosphate) is a coenzyme involved in decarboxylation reactions. Therefore, the correct answer is Coenzyme A and lipoamide.

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  • 9. 

    Which cofactors of the pyruvate dehydrogenase reaction are permanently bound?

    • Thiamine pyrophosphate

    • Lipoamide

    • Flavin adenine dinucleotide

    • Nicotinamide adenine dinucleotide

    • Coenzyme A

    Correct Answer(s)
    A. Thiamine pyrophosphate
    A. Lipoamide
    A. Flavin adenine dinucleotide
    Explanation
    Thiamine pyrophosphate, lipoamide, and flavin adenine dinucleotide are permanently bound cofactors in the pyruvate dehydrogenase reaction. This means that they are tightly bound to the enzyme and participate in the reaction without being released or consumed. These cofactors play essential roles in catalyzing the conversion of pyruvate to acetyl-CoA, which is an important step in cellular respiration. Thiamine pyrophosphate is involved in decarboxylation reactions, lipoamide acts as a carrier of acetyl groups, and flavin adenine dinucleotide is a redox cofactor.

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  • 10. 

    Which PRODUCTS are not formed when there is an excess of ATP and NADH?

    • Acetyl CoA

    • α-ketoglutarate

    • Succinyl-CoA

    • Isocitrate

    • Pyruvate

    Correct Answer(s)
    A. Acetyl CoA
    A. α-ketoglutarate
    A. Succinyl-CoA
    Explanation
    When there is an excess of ATP and NADH, the citric acid cycle (also known as the Krebs cycle) slows down. Acetyl CoA, α-ketoglutarate, and succinyl-CoA are all intermediates in the citric acid cycle, which means they are produced and consumed during the cycle. However, when there is an excess of ATP and NADH, the cycle slows down and fewer intermediates are formed. Therefore, Acetyl CoA, α-ketoglutarate, and succinyl-CoA are not formed in sufficient quantities when there is an excess of ATP and NADH.

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  • Current Version
  • Mar 21, 2023
    Quiz Edited by
    ProProfs Editorial Team
  • Aug 05, 2020
    Quiz Created by
    Iyanna Peppers
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