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Quizzes > High School Quizzes > Science

Glycolysis and Krebs Cycle Practice Quiz

Master metabolic pathways with engaging POGIL review

Difficulty: Moderate
Grade: Grade 11
Study OutcomesCheat Sheet
Paper art illustrating Metabolic Mayhem trivia challenge for high school biology students.

Easy
In which part of the cell does glycolysis occur?
Mitochondria
Endoplasmic reticulum
Nucleus
Cytoplasm
Glycolysis takes place in the cytoplasm where glucose is broken down into pyruvate. This process occurs outside the mitochondria, making it independent of oxygen availability.
What is the net ATP gain produced during glycolysis from one molecule of glucose?
2 ATP
4 ATP
8 ATP
10 ATP
Glycolysis generates a total of 4 ATP molecules but uses 2 ATP in the initial steps. This results in a net gain of 2 ATP per glucose molecule.
What is the end product of glycolysis?
Citrate
Lactate
Acetyl-CoA
Pyruvate
Glycolysis converts one glucose molecule into two molecules of pyruvate. Under aerobic conditions, pyruvate is further converted into Acetyl-CoA for the Krebs cycle.
What is the primary function of the Krebs cycle?
To break down proteins into amino acids
To store energy in the form of fatty acids
To oxidize Acetyl-CoA and generate high-energy electron carriers
To synthesize glucose from pyruvate
The Krebs cycle oxidizes Acetyl-CoA to produce NADH and FADH2, which are essential for ATP production in the electron transport chain. This cycle is central to cellular respiration and energy production.
In which cellular organelle does the Krebs cycle take place?
Endoplasmic reticulum
Cytoplasm
Mitochondrial matrix
Nucleus
The Krebs cycle occurs within the mitochondrial matrix where the enzymes and substrates necessary for the cycle are located. This environment supports the efficient production of electron carriers for further energy generation.
Medium
Which enzyme catalyzes the rate-limiting step in glycolysis, converting fructose-6-phosphate to fructose-1,6-bisphosphate?
Phosphofructokinase
Hexokinase
Aldolase
Pyruvate kinase
Phosphofructokinase (PFK) is the key regulatory enzyme that catalyzes an irreversible step in glycolysis. This reaction commits the cell to breaking down glucose for energy.
Under aerobic conditions, what transformation does pyruvate undergo before entering the Krebs cycle?
Formation of ethanol
Direct entry into the Krebs cycle
Conversion to lactate
Conversion into Acetyl-CoA
In the presence of oxygen, pyruvate is converted into Acetyl-CoA by the pyruvate dehydrogenase complex. This conversion is essential for linking glycolysis to the Krebs cycle.
Which intermediate is directly produced by the cleavage of fructose-1,6-bisphosphate in glycolysis?
Citrate
Acetyl-CoA
Glyceraldehyde-3-phosphate
Pyruvate
The enzyme aldolase cleaves fructose-1,6-bisphosphate into two three-carbon molecules, one of which is glyceraldehyde-3-phosphate (GAP). GAP continues through glycolysis to contribute to energy production.
Which molecule is regenerated at the end of the Krebs cycle to enable the continuation of the cycle?
NADH
Acetyl-CoA
Oxaloacetate
ATP
Oxaloacetate is the molecule that reacts with Acetyl-CoA to start the Krebs cycle and is regenerated by the cycle's end. Its continuous regeneration is vital for the cyclical nature of this metabolic pathway.
In the Krebs cycle, which reaction is responsible for a direct substrate-level phosphorylation event producing GTP (or ATP)?
Conversion of α-ketoglutarate to Succinyl-CoA
Conversion of isocitrate to α-ketoglutarate
Conversion of Succinyl-CoA to Succinate
Conversion of citrate to isocitrate
The step converting Succinyl-CoA to Succinate is coupled with substrate-level phosphorylation that produces GTP (or ATP). This reaction is unique in directly generating a high-energy phosphate compound in the cycle.
Which high-energy electron carrier is produced during both the glycolytic pathway and the Krebs cycle?
FADH2
NADH
ATP
GTP
NADH is produced in glycolysis during the conversion of glyceraldehyde-3-phosphate and is also generated at multiple steps during the Krebs cycle. It plays a critical role in transferring electrons to the electron transport chain for ATP synthesis.
What is the impact of elevated ATP concentrations on the enzyme phosphofructokinase in glycolysis?
It has no effect on phosphofructokinase
It inhibits phosphofructokinase activity
It converts phosphofructokinase into an inactive form
It stimulates phosphofructokinase activity
High ATP levels signal that the cell has sufficient energy, leading to the inhibition of phosphofructokinase by allosteric regulation. This inhibition slows glycolysis, preventing overproduction of ATP.
What is the molecule that condenses with oxaloacetate to form citrate in the Krebs cycle?
Succinyl-CoA
NADH
Pyruvate
Acetyl-CoA
Acetyl-CoA combines with oxaloacetate to form citrate in the first, irreversible step of the Krebs cycle. This condensation reaction, catalyzed by citrate synthase, marks the entry point into the cycle.
Which specific step in glycolysis results in the direct production of NADH?
Conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate
Conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate
Conversion of phosphoenolpyruvate to pyruvate
Conversion of glucose to glucose-6-phosphate
The oxidation of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate is coupled with the reduction of NAD+ to NADH. This reaction is a pivotal step linking substrate-level phosphorylation with the cell's redox processes.
How many enzymatic steps are involved in the complete glycolytic pathway?
14 steps
8 steps
12 steps
10 steps
Glycolysis consists of 10 enzyme-catalyzed reactions that systematically break down glucose into pyruvate. This number of steps reflects the complexity and regulation of the pathway.
Hard
Which cofactor is essential for the function of the enzyme that catalyzes the oxidative decarboxylation of α-ketoglutarate to succinyl-CoA in the Krebs cycle?
Thiamine pyrophosphate
Riboflavin
NADH
Biotin
Thiamine pyrophosphate (TPP) is a critical cofactor for the α-ketoglutarate dehydrogenase complex, which facilitates the conversion of α-ketoglutarate to succinyl-CoA. This cofactor stabilizes the reaction intermediate during the decarboxylation process.
Why does NADH produced in the cytosol during glycolysis often yield less ATP when it enters the electron transport chain compared to NADH generated in the mitochondrial matrix?
Because cytosolic NADH requires shuttle mechanisms that reduce its ATP yield
Because cytosolic NADH bypasses the electron transport chain entirely
Because cytosolic NADH is more efficient at donating electrons
There is no difference in ATP yield between cytosolic and mitochondrial NADH
NADH produced in the cytosol must be transported into the mitochondria via shuttle systems, which can lead to a reduced ATP yield. In contrast, mitochondrial NADH directly enters the electron transport chain, enabling a more efficient production of ATP.
Which metabolite, when accumulated, can inhibit phosphofructokinase as part of the regulation of glycolysis?
Oxaloacetate
Citrate
Fructose-1,6-bisphosphate
Lactate
Citrate accumulation signals that the cell's energy needs are met, and it acts as an allosteric inhibitor of phosphofructokinase. This feedback mechanism helps coordinate the flux of glycolysis with the energy demands of the cell.
Which enzyme catalyzes the irreversible condensation reaction between Acetyl-CoA and oxaloacetate to form citrate in the Krebs cycle?
Citrate synthase
Aconitase
Succinate dehydrogenase
Isocitrate dehydrogenase
Citrate synthase catalyzes the first committed and irreversible step of the Krebs cycle by condensing Acetyl-CoA with oxaloacetate to form citrate. This reaction is a major regulatory point in cellular metabolism.
In glycolysis, how does the energy investment phase compare to the energy payoff phase in terms of ATP molecules?
The investment phase consumes 2 ATP and the payoff phase produces 4 ATP, resulting in a net gain of 2 ATP
The investment phase consumes 2 ATP and the payoff phase produces 6 ATP, resulting in a net gain of 4 ATP
The investment phase consumes 4 ATP and the payoff phase produces 6 ATP, resulting in a net gain of 2 ATP
The investment phase consumes 2 ATP and the payoff phase produces 2 ATP, resulting in no net gain
Glycolysis begins with an investment of 2 ATP molecules, which are later surpassed by the production of 4 ATP in the energy payoff phase. This results in a net gain of 2 ATP per glucose molecule, which is fundamental to the pathway's efficiency.
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Study Outcomes

  1. Analyze the step-by-step processes of glycolysis.
  2. Explain the key reactions and intermediates of the Krebs cycle.
  3. Compare the roles and outcomes of glycolysis and the Krebs cycle.
  4. Apply knowledge of enzyme regulation to metabolic pathways.
  5. Evaluate the energy yields produced during metabolic processes.
  6. Synthesize concepts to predict metabolic responses under different conditions.

Glycolysis & Krebs Cycle POGIL Cheat Sheet

  1. Glycolysis - This anaerobic pathway breaks down glucose into two pyruvate molecules in the cytoplasm, producing a net gain of 2 ATP and 2 NADH. It's like the cell's quick cash withdrawal at the energy ATM! Understanding this kickstart is key to mastering how cells fuel up. Glycolysis - Wikipedia
  2. Citric Acid Cycle - The Krebs cycle turns acetyl‑CoA into CO₂ while generating 3 NADH, 1 FADH₂, and 1 ATP (or GTP) per turn in the mitochondrial matrix. This cyclical dance is the powerhouse of aerobic energy production and a hub for biosynthesis. Getting comfy with its steps helps you see the big picture of cellular respiration. Citric Acid Cycle - Wikipedia
  3. Pyruvate Oxidation - Acting as the bridge between glycolysis and the Krebs cycle, pyruvate oxidation converts pyruvate into acetyl‑CoA while releasing CO₂ and making NADH. Without this gatekeeper step, the aerobic party can't go on! Remembering this conversion keeps your energy flow on track. Glycolysis & Krebs Cycle Breakdown
  4. Enzyme Regulation - Hexokinase and phosphofructokinase are the traffic cops of glycolysis, throttling the pathway based on ATP levels. When energy is abundant, they slam the brakes; when energy is low, they give a green light. This dynamic regulation ensures cells only produce what they need. Glycolysis - Wikipedia
  5. Amphibolic Nature - The Krebs cycle moonlights as both a catabolic and anabolic pathway, breaking molecules down for energy and building blocks simultaneously. It's like a Swiss Army knife in your metabolism toolkit! Appreciating this dual role reveals why the cycle is so versatile and vital. Krebs Cycle - BYJU'S
  6. Substrate‑Level Phosphorylation - In glycolysis and the Krebs cycle, ATP is directly made when enzymes transfer phosphate groups to ADP. This fast‑track method supplies immediate energy without waiting for the electron transport chain. It's your cell's instant gratification system! Glycolysis - Wikipedia
  7. Electron Carriers - NADH and FADH₂ literally carry the charges from glycolysis and the Krebs cycle over to the electron transport chain, where even more ATP is generated. Think of them as VIP passes into the ultimate energy concert. Without these carriers, the ETC can't rock on. Citric Acid Cycle - Wikipedia
  8. Krebs Regulation - High levels of ATP and NADH inhibit key Krebs cycle enzymes like citrate synthase and isocitrate dehydrogenase to prevent overproduction. This feedback ensures metabolic harmony and stops cells from wasting resources. It's like an internal thermostat that keeps energy production in check. Krebs Cycle - Biology Notes Online
  9. Mnemonic Magic - Use a catchy phrase like "Citrate Is Krebs' Starting Substrate For Making Oxaloacetate" to lock in the order: Citrate, Isocitrate, α‑Ketoglutarate, Succinyl‑CoA, Succinate, Fumarate, Malate, Oxaloacetate. Turning complex lists into fun slogans makes memory a breeze! Mnemonics are your best study buddies. Krebs Cycle - BYJU'S
  10. Pathway Integration - Glycolysis, the Krebs cycle, and the electron transport chain form a seamless relay to turn glucose into ATP. Picture it as a high‑energy baton pass where efficiency is everything. Grasping this connection ties all your respiration studies together in an epic grand finale! Glycolysis & Krebs Cycle Breakdown
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