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Quizzes > Science

Citric Acid Cycle Quiz: Check your Krebs cycle knowledge

Quick, free TCA cycle quiz with instant results and helpful explanations.

Editorial: Review CompletedCreated By: Christian KazanjianUpdated Aug 23, 2025
Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration for Citric Acid Cycle quiz on golden yellow background

This citric acid cycle quiz helps you review each step of the Krebs cycle and see how carbon, energy carriers, and ATP connect. Use it to check what you know before class or an exam, then deepen your practice with the glycolysis pathway quiz, explore a broader biochemistry quiz, or switch it up with a krebs cycle game.

Which cellular compartment houses the citric acid (Krebs) cycle in eukaryotic cells?
Nucleus
Endoplasmic reticulum lumen
Mitochondrial matrix
Cytosol
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The citric acid cycle begins when acetyl-CoA condenses with which four-carbon molecule to form citrate?
Malate
Oxaloacetate
Succinate
Fumarate
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Per turn of the citric acid cycle (from one acetyl-CoA), how many molecules of CO2 are released?
2
3
1
4
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In aerobic metabolism, most ATP derived from the citric acid cycle comes indirectly from which process?
Glycolysis payoff phase
Substrate-level phosphorylation in the cycle
Pentose phosphate pathway
Electron transport chain oxidative phosphorylation
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Which coenzyme is reduced to FADH2 during the citric acid cycle?
At citrate synthase
At malate dehydrogenase
At isocitrate dehydrogenase
At succinate dehydrogenase
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Per acetyl-CoA oxidized, how many NADH are generated in the citric acid cycle?
1
2
4
3
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Which enzyme catalyzes the isomerization of citrate to isocitrate via cis-aconitate?
Citrate synthase
Fumarase
Aconitase
Isocitrate dehydrogenase
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Which step of the citric acid cycle directly produces GTP (or ATP depending on tissue)?
Succinyl-CoA to succinate
alpha-Ketoglutarate to succinyl-CoA
Citrate to isocitrate
Malate to oxaloacetate
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Succinate dehydrogenase is uniquely associated with which component of the respiratory chain?
Complex II
Complex IV
Complex III
Complex I
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Which of the following is an irreversible step in the citric acid cycle?
Malate dehydrogenase reaction
Aconitase reaction
Citrate synthase reaction
Fumarase reaction
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Which molecule is a key activator of isocitrate dehydrogenase in muscle?
Citrate
Calcium ions (Ca2+)
NADH
ATP
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In mammals, succinyl-CoA synthetase can produce GTP in some tissues. Which enzyme converts this GTP to ATP?
Nucleoside diphosphate kinase
ATP synthase
Creatine kinase
Adenylate kinase
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The carbons released as CO2 in one turn of the cycle originate from which source during that turn?
They come from oxaloacetate-derived carbons
They come directly from the incoming acetyl-CoA carbons
They come from malate exclusively
They come from mitochondrial CO2 pool
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Which compound is a competitive inhibitor of succinate dehydrogenase?
Arsenite
Oligomycin
Fluoroacetate
Malonate
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Which enzyme of the citric acid cycle contains an iron-sulfur cluster required for its function?
Malate dehydrogenase
Fumarase
Aconitase
Citrate synthase
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Fluoroacetate toxicity arises because fluoroacetate is converted to which compound that traps citrate synthase flux?
Fluorocitrate
Fluorosuccinate
Fluoromalate
Fluoropyruvate
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The alpha-ketoglutarate dehydrogenase complex requires which cofactor also used by pyruvate dehydrogenase?
Biotin
Pyridoxal phosphate (PLP)
Cobalamin
Thiamine pyrophosphate (TPP)
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Which metabolite accumulation can inhibit prolyl hydroxylases, stabilizing HIF under certain pathological conditions?
Oxaloacetate
Citrate
Malate
Succinate
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Substrate channeling within the alpha-ketoglutarate dehydrogenase complex primarily enhances which property?
Membrane permeability
Catalytic efficiency and reduced diffusion of intermediates
Thermal stability
Light absorption
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Which statement about malate dehydrogenase in the cycle is correct?
It produces GTP
It oxidizes malate to fumarate
It reduces FAD and is highly exergonic
It reduces NAD+ and has a strongly positive delta G under matrix conditions
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Study Outcomes

  1. Recall Key Intermediates -

    Identify and memorize the main substrates and products in each step of the citric acid cycle quiz to reinforce your metabolic pathway knowledge.

  2. Explain Enzymatic Roles -

    Describe the function of critical enzymes in the TCA cycle quiz and how they facilitate energy production during cellular respiration.

  3. Analyze Regulatory Mechanisms -

    Examine the control points within the Krebs cycle quiz to understand how flux is adjusted in response to cellular energy demands.

  4. Apply Metabolic Integration -

    Connect the citric acid cycle game to glycolysis and the electron transport chain to see how carbon flow affects overall ATP yield.

  5. Predict Pathway Outcomes -

    Use quiz scenarios to anticipate changes in metabolite levels under varying conditions, such as high NADH or low oxygen.

  6. Evaluate Energy Yield -

    Calculate the net production of NADH, FADH₂, and GTP per cycle turn to gauge the efficiency of cellular respiration.

Cheat Sheet

  1. Entry of Acetyl-CoA and Citrate Formation -

    Acetyl-CoA condenses with oxaloacetate via citrate synthase to form citrate in a highly exergonic reaction (Nelson & Cox, Lehninger Principles). This committed step drives the TCA cycle forward and is tightly regulated to match cellular energy demand.

  2. Oxidative Decarboxylation Steps -

    Isocitrate dehydrogenase converts isocitrate to α-ketoglutarate, releasing CO₂ and reducing NAD❺ to NADH, followed by α-ketoglutarate dehydrogenase generating succinyl-CoA, another CO₂, and NADH (Alberts et al., Molecular Biology of the Cell). These two key steps account for two of the cycle's three NADH-producing oxidations.

  3. Substrate-Level Phosphorylation and GTP/ATP Generation -

    Succinyl-CoA synthetase catalyzes the conversion of succinyl-CoA to succinate, coupled to GTP (or ATP) formation via nucleoside diphosphate kinase, representing the sole substrate-level phosphorylation in the TCA cycle (Voet & Voet, Biochemistry). This step provides direct energy currency before further oxidation.

  4. Mnemonics for Cycle Intermediates -

    Use "Citrate Is Krebs' Starting Substrate For Making Oxaloacetate" to recall the eight intermediates in order: citrate, isocitrate, α-ketoglutarate, succinyl-CoA, succinate, fumarate, malate, oxaloacetate. This mnemonic is invaluable for quick recall during a citric acid cycle quiz or tca cycle quiz and boosts retention under pressure.

  5. Regulation by Key Enzymes -

    Citrate synthase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase are the primary control points, responding to ATP/ADP ratios, NADH levels, and availability of substrates (FDA Handbook on Metabolic Regulation). Allosteric activators like ADP enhance flux, while NADH and ATP act as feedback inhibitors to balance energy production with demand.

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