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Quizzes > Science > Biology

Put Your Glycolysis & Krebs Cycle Knowledge to the Test!

Think you can ace this glycolysis game? Take on the citric acid cycle challenge!

Difficulty: Moderate
2-5mins
Learning OutcomesCheat Sheet
Paper art illustration of glycolysis and Krebs cycle quiz with stylized enzymes pathways on teal background.

Ready to dive into the heart of cellular energy production? Our Ace the Glycolysis & Krebs Cycle Quiz is the ultimate krebs cycle quiz - perfect for biochemistry buffs eager to explore glycolysis and krebs in action! Whether you want to sharpen your skills with a glycolysis game or tackle the tca cycle game, this interactive challenge helps you track your score, master each step in the citric acid cycle game, and reinforce key metabolic checkpoints. Ready to jump in? Try our Glycolysis Quiz to warm up, then delve into the krebs cycle and electron transport chain . Don't wait - uncover the secrets of metabolism now!

What is the net yield of ATP molecules per glucose molecule during glycolysis?
2
4
1
3
Glycolysis invests two ATP in its preparatory phase and produces four ATP in the payoff phase, for a net yield of two ATP per glucose molecule. Wikipedia Glycolysis
In which cellular compartment does glycolysis occur?
Cytosol
Mitochondrial matrix
Endoplasmic reticulum
Golgi apparatus
All enzymes of glycolysis are located in the cytosol, while the Krebs cycle and oxidative phosphorylation occur in the mitochondria. NCBI Glycolysis
Under anaerobic conditions in muscle cells, what is the end product of glycolysis?
Pyruvate
Lactate
Acetyl-CoA
Ethanol
In anaerobic muscle, pyruvate is reduced to lactate by lactate dehydrogenase to regenerate NAD+ for continued glycolysis. Wikipedia Lactic Acid Fermentation
Which enzyme catalyzes the phosphorylation of glucose to glucose-6-phosphate in the first step of glycolysis?
Hexokinase
Phosphofructokinase-1
Pyruvate kinase
Aldolase
Hexokinase uses ATP to phosphorylate glucose to glucose-6-phosphate, trapping glucose inside the cell. Wikipedia Hexokinase
How many ATP molecules are consumed in the preparatory phase of glycolysis per molecule of glucose?
2
4
1
3
Two ATP molecules are invested in the preparatory phase: one to phosphorylate glucose and one to phosphorylate fructose-6-phosphate. NCBI Glycolysis Overview
Which enzyme catalyzes the rate-limiting step of glycolysis?
Hexokinase
Phosphofructokinase-1
Glyceraldehyde-3-phosphate dehydrogenase
Enolase
Phosphofructokinase-1 is the major regulatory enzyme of glycolysis, controlling pathway flux in response to cellular energy status. Wikipedia PFK-1
In the Krebs cycle, which molecule donates electrons to the electron transport chain after its production?
ATP
NADH
GTP
CO2
NADH carries high-energy electrons from dehydrogenase reactions to the electron transport chain, driving ATP synthesis. Wikipedia NADH
In the Krebs cycle, acetyl-CoA combines with which molecule to form citrate?
Alpha-ketoglutarate
Oxaloacetate
Succinate
Malate
Citrate synthase catalyzes the condensation of acetyl-CoA with oxaloacetate to form citrate, the first step of the cycle. Wikipedia Citrate Synthase
How many CO2 molecules are released per acetyl-CoA molecule oxidized in the Krebs cycle?
1
2
3
4
Two CO2 are released: one during isocitrate to alpha-ketoglutarate, and one during alpha-ketoglutarate to succinyl-CoA. NCBI Krebs Cycle
Which step in glycolysis generates the first NADH molecule?
Conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate
Phosphorylation of fructose-6-phosphate
Dehydration of 2-phosphoglycerate
Conversion of phosphoenolpyruvate to pyruvate
Glyceraldehyde-3-phosphate dehydrogenase oxidizes glyceraldehyde-3-phosphate, producing NADH and 1,3-bisphosphoglycerate. Wikipedia GAPDH
What is the role of phosphoglucose isomerase in glycolysis?
Converts glucose to glucose-6-phosphate
Converts glucose-6-phosphate to fructose-6-phosphate
Converts fructose-1,6-bisphosphate to glyceraldehyde-3-phosphate
Converts 2-phosphoglycerate to phosphoenolpyruvate
Phosphoglucose isomerase isomerizes glucose-6-phosphate into fructose-6-phosphate in a reversible step of glycolysis. Wikipedia PGI
Which enzyme in the Krebs cycle directly generates GTP (or ATP) through substrate-level phosphorylation?
Succinate dehydrogenase
Succinyl-CoA synthetase
Citrate synthase
Alpha-ketoglutarate dehydrogenase
Succinyl-CoA synthetase converts succinyl-CoA to succinate, coupling this reaction to GTP formation via substrate-level phosphorylation. Wikipedia Succinyl-CoA Synthetase
How many NADH molecules are produced per acetyl-CoA oxidized in the Krebs cycle?
1
2
3
0
Three NADH are produced at isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase, and malate dehydrogenase steps per acetyl-CoA. Wikipedia Krebs Cycle
Which enzyme catalyzes the final step of glycolysis, converting phosphoenolpyruvate to pyruvate?
Enolase
Pyruvate kinase
Lactate dehydrogenase
Pyruvate dehydrogenase
Pyruvate kinase transfers a phosphate from PEP to ADP, producing pyruvate and ATP in glycolysis's final step. Wikipedia Pyruvate Kinase
Which enzyme of the Krebs cycle is embedded in the inner mitochondrial membrane and feeds electrons directly into the electron transport chain?
Aconitase
Succinate dehydrogenase
Isocitrate dehydrogenase
Citrate synthase
Succinate dehydrogenase (complex II) is membrane-bound and transfers electrons from succinate to ubiquinone in the ETC. Wikipedia Succinate Dehydrogenase
Which cofactor is essential for the pyruvate dehydrogenase complex to decarboxylate pyruvate?
Biotin
Thiamine pyrophosphate
Pyridoxal phosphate
FAD
Thiamine pyrophosphate (vitamin B1) binds to E1 and aids decarboxylation of pyruvate, forming a hydroxyethyl-TPP intermediate. Wikipedia Pyruvate Dehydrogenase
What intermediate links glycolysis to the Krebs cycle after pyruvate oxidation?
Oxaloacetate
Pyruvate
Acetyl-CoA
Citrate
Pyruvate is converted by PDH into acetyl-CoA, which then enters the Krebs cycle by combining with oxaloacetate. Wikipedia Acetyl-CoA
How many ATP molecules (theoretical) are produced by the oxidation of one NADH molecule via oxidative phosphorylation?
1
2
3
4
Traditionally, each NADH yields about three ATP through the electron transport chain, though modern estimates are closer to 2.5. Wikipedia Proton-motive Force
In gluconeogenesis, which enzyme bypasses the irreversible pyruvate kinase step of glycolysis by converting oxaloacetate to phosphoenolpyruvate?
Pyruvate carboxylase
Phosphoenolpyruvate carboxykinase
Pyruvate kinase
Enolase
PEP carboxykinase converts oxaloacetate to PEP, circumventing pyruvate kinase, a key regulatory step in gluconeogenesis. Wikipedia PEPCK
Which enzyme in the Krebs cycle is allosterically activated by ADP?
Citrate synthase
Aconitase
Isocitrate dehydrogenase
Succinate dehydrogenase
Isocitrate dehydrogenase is activated by ADP, signaling low energy and increasing the cycle’s throughput. Wikipedia Isocitrate Dehydrogenase
During intense exercise, which process allows ATP generation independent of oxygen?
Pentose phosphate pathway
Lactic acid fermentation
Beta-oxidation
Gluconeogenesis
Under anaerobic conditions, lactic acid fermentation regenerates NAD+ to sustain glycolysis and ATP production without oxygen. Wikipedia Lactic Acid Fermentation
A deficiency in pyruvate dehydrogenase would most likely cause accumulation of which metabolite?
Citrate
Lactate
Oxaloacetate
Succinate
If PDH is impaired, pyruvate cannot form acetyl-CoA and is diverted to lactate, leading to lactic acidosis. NCBI PDH Deficiency
Which Krebs cycle intermediate can be transaminated to form the amino acid glutamate?
Succinyl-CoA
Fumarate
Alpha-ketoglutarate
Oxaloacetate
Alpha-ketoglutarate accepts an amino group via transamination to form glutamate, linking carbon and nitrogen metabolism. Wikipedia ?-Ketoglutarate
What is the principal function of the malate-aspartate shuttle?
Generate NADPH for biosynthesis
Transport reducing equivalents from cytosolic NADH into mitochondria
Export ATP from mitochondria to cytosol
Convert lactate to pyruvate
The malate-aspartate shuttle transfers cytosolic NADH electrons into mitochondria by interconverting malate and oxaloacetate. Wikipedia Malate-Aspartate Shuttle
The complete oxidation of one glucose molecule via glycolysis, the Krebs cycle, and oxidative phosphorylation produces approximately how many ATP molecules (theoretical)?
28
30
32
36
Classical bioenergetics estimates about 32 ATP per glucose: 2 from glycolysis, 2 GTP from the cycle, and ~28 from NADH/FADH2 oxidation. NCBI Bioenergetics
Which enzyme catalyzes the reversible hydration of fumarate to malate in the Krebs cycle?
Fumarase
Enolase
Malate dehydrogenase
Aconitase
Fumarase adds water across the double bond of fumarate to form malate, a reversible reaction in the cycle. Wikipedia Fumarase
The activation of phosphofructokinase-1 by fructose-2,6-bisphosphate is an example of which type of regulation?
Competitive inhibition
Allosteric activation
Covalent modification
Feedback inhibition
Fructose-2,6-bisphosphate binds to an allosteric site on PFK-1, increasing its activity and enhancing glycolysis. Wikipedia Fructose-2,6-BP
The lipoamide prosthetic group on the E2 subunit of the pyruvate dehydrogenase complex facilitates which key reaction?
It transfers the acetyl group from TPP to CoA
It decarboxylates pyruvate to form acetaldehyde
It oxidizes NADH to NAD+
It carboxylates pyruvate to oxaloacetate
Lipoamide swings between E1 and E2, accepting the hydroxyethyl moiety from TPP to form acetyllipoamide, which then transfers the acetyl group to CoA. Wikipedia Pyruvate Dehydrogenase
In the glyoxylate cycle, which enzyme bypasses the decarboxylation steps of the Krebs cycle to conserve carbon skeletons?
Isocitrate lyase
Malate dehydrogenase
Aconitase
Succinate dehydrogenase
Isocitrate lyase cleaves isocitrate into succinate and glyoxylate, bypassing CO?-producing steps and conserving carbon for gluconeogenesis. Wikipedia Glyoxylate Cycle
The large negative ?G°' for the glyceraldehyde-3-phosphate dehydrogenase reaction in glycolysis is primarily due to which intracellular condition?
High ATP/ADP ratio
High NAD+/NADH ratio
High concentration of 3-phosphoglycerate
Low concentration of glyceraldehyde-3-phosphate
A high NAD?/NADH ratio drives the oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, making the reaction strongly exergonic under physiological conditions. Wikipedia GAPDH Reaction
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Study Outcomes

  1. Calculate ATP Yield -

    Determine the number of ATP molecules produced at key steps of glycolysis and the citric acid cycle using our interactive quiz format.

  2. Identify Key Enzymes -

    Recognize and recall the main enzymes that catalyze each reaction in the glycolysis game and Krebs cycle quiz.

  3. Differentiate Critical Intermediates -

    Distinguish important metabolites, such as fructose-1,6-bisphosphate and citrate, within the pathways of our TCA cycle game.

  4. Analyze Regulatory Points -

    Evaluate major control sites and allosteric regulators that govern metabolic flux during the quiz challenges.

  5. Apply Mechanistic Knowledge -

    Use your understanding of enzyme functions and reaction steps to solve citric acid cycle practice problems accurately.

  6. Assess Pathway Integration -

    Connect how glycolysis and the Krebs cycle interlink to overall cellular energy production in our metabolism mastery quiz.

Cheat Sheet

  1. Glycolysis Overall Reaction & Net ATP Yield -

    Glycolysis converts one glucose molecule into two pyruvates with a net gain of 2 ATP and 2 NADH per glucose (Lehninger Principles of Biochemistry, 7th ed.). Remember the overall equation: C₆Hâ‚â‚‚O₆ + 2 NAD⺠+ 2 ADP + 2 Pi → 2 CH₃COCOOâ» + 2 NADH + 2 H⺠+ 2 ATP + 2 Hâ‚‚O. This foundation is critical for any krebs cycle quiz or glycolysis game challenge.

  2. Key Regulatory Enzymes in Glycolysis -

    Three enzymes - hexokinase, phosphofructokinase-1 (PFK-1), and pyruvate kinase - act as major control points (Harvard Biochemistry Department). PFK-1, the rate-limiting step, is allosterically activated by AMP and inhibited by ATP and citrate. Understanding these controls is essential when playing a citric acid cycle game or tca cycle game to anticipate metabolic shifts.

  3. Mnemonic for Glycolytic Intermediates -

    Use "Goodness Gracious, Father Franklin Did Go By Picking Pumpkins (to) Prepare Pies" to recall Glucose, Glucose-6-phosphate, Fructose-6-phosphate, Fructose-1,6-bisphosphate, DHAP, G3P, 1,3-Bisphosphoglycerate, 3PG, 2PG, PEP, Pyruvate (University of Cambridge Biochemistry Dept.). This vivid phrase helps cement the 10-step pathway in memory for any glycolysis and krebs quiz. Pair it with flashcards showing structures to boost retention.

  4. TCA Cycle Energy Yield per Acetyl-CoA -

    Each acetyl-CoA entering the Krebs cycle produces 3 NADH, 1 FADHâ‚‚, and 1 GTP (or ATP) through eight enzymatic steps (Voet & Voet, Biochemistry, 4th ed.). This translates roughly to 10 ATP equivalents after oxidative phosphorylation. Mastering these yields will give you an edge in any krebs cycle quiz or citric acid cycle game.

  5. Link Reaction & Pyruvate Dehydrogenase Complex -

    The pyruvate dehydrogenase complex (PDC) bridges glycolysis and the TCA cycle, converting pyruvate into acetyl-CoA while requiring five cofactors: TPP, lipoate, CoA, FAD, and NAD⺠(National Institutes of Health). PDC is tightly regulated by phosphorylation (inhibitory) and dephosphorylation (activating) mechanisms. Grasping this control is key for any tca cycle game or krebs cycle quiz scenario.

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