Citric Acid Cycle Quiz

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Questions and Answers

What is the name of the enzyme that catalyzes the reaction between acetyl CoA and oxaloacetate?

  • α-ketoglutarate dehydrogenase
  • Citrate synthase (correct)
  • Isocitrate dehydrogenase
  • Pyruvate dehydrogenase

What is the net effect of the reaction shown in the diagram?

  • The conversion of oxaloacetate to citrate
  • The removal of a two-carbon unit from oxaloacetate
  • The conversion of citrate to oxaloacetate
  • The addition of a two-carbon unit to oxaloacetate (correct)

What is the role of CoA in the reaction shown in the diagram?

  • CoA acts as a catalyst for the reaction
  • CoA acts as a carrier of the acetyl group (correct)
  • CoA is a product of the reaction
  • CoA is a substrate of the reaction

What is the name of the six-carbon molecule that is formed in the reaction shown in the diagram?

<p>Citrate (C)</p> Signup and view all the answers

What is the product of the next reaction in the citric acid cycle, catalyzed by aconitase?

<p>Isocitrate (B)</p> Signup and view all the answers

What is the immediate product of the oxidation of isocitrate?

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

What molecule is oxidized during the conversion of isocitrate to α-ketoglutarate?

<p>Isocitrate (D)</p> Signup and view all the answers

During the conversion of isocitrate to α-ketoglutarate, what molecule is reduced?

<p>NAD+ (A)</p> Signup and view all the answers

What is the primary function of isocitrate dehydrogenase in the citric acid cycle?

<p>To catalyze the oxidation of isocitrate (C)</p> Signup and view all the answers

What is the net change in the number of carbon atoms in the molecule during the conversion of isocitrate to α-ketoglutarate?

<p>The number of carbon atoms decreases by 1. (C)</p> Signup and view all the answers

What is the primary function of the Krebs cycle (Citric Acid Cycle)?

<p>To produce ATP, NADH, and FADH2 for later use in oxidative phosphorylation (D)</p> Signup and view all the answers

How many molecules of ATP are produced directly during the Krebs cycle per molecule of glucose?

<p>2 (D)</p> Signup and view all the answers

What molecule is produced by the combination of acetyl-CoA (2C) and oxaloacetate (4C)?

<p>Citrate (6C) (B)</p> Signup and view all the answers

What are the primary products of the Krebs cycle?

<p>ATP, NADH, and FADH2 (D)</p> Signup and view all the answers

What type of reaction occurs during the Krebs cycle when carbon dioxide molecules are released?

<p>Decarboxylation (A)</p> Signup and view all the answers

Which of the following is NOT a synonym for the Krebs cycle?

<p>Glycolysis (B), Electron Transport Chain (C)</p> Signup and view all the answers

What role does oxygen play in the Krebs cycle?

<p>Oxygen is not directly involved in the Krebs cycle but is essential for the electron transport chain. (B)</p> Signup and view all the answers

Where does the Krebs cycle take place within the cell?

<p>Mitochondrial matrix (D)</p> Signup and view all the answers

What is the fate of the NADH and FADH2 produced in the Krebs cycle?

<p>They are passed to the Electron Transport Chain for further energy production. (B)</p> Signup and view all the answers

How many molecules of pyruvate are produced from a single molecule of glucose?

<p>2 (D)</p> Signup and view all the answers

What is the main function of the electron transport chain (ETC) in cellular respiration?

<p>To generate a proton gradient across the mitochondrial membrane (C)</p> Signup and view all the answers

In the citric acid cycle, what molecule is oxidized by malate dehydrogenase?

<p>Malate (D)</p> Signup and view all the answers

What is the ultimate fate of NADH and FADH2 produced in the citric acid cycle?

<p>They are used to generate ATP through oxidative phosphorylation (B)</p> Signup and view all the answers

Which of the following molecules contributes to the formation of the proton gradient in the intermembrane space?

<p>NADH (A), FADH2 (D)</p> Signup and view all the answers

What is the name of the process that uses the proton gradient to synthesize ATP?

<p>Chemiosmosis (D)</p> Signup and view all the answers

Where does oxidative phosphorylation occur?

<p>Inner membrane of mitochondria (A)</p> Signup and view all the answers

Where does the energy come from that drives the pumping of protons across the mitochondrial membrane?

<p>The transfer of electrons down the ETC (A), The oxidation of NADH and FADH2 (C)</p> Signup and view all the answers

What is the role of GDP and Pi in the citric acid cycle?

<p>They are used to generate GTP (B)</p> Signup and view all the answers

What is the net gain of ATP per glucose molecule from glycolysis, the citric acid cycle, and oxidative phosphorylation?

<p>38 ATP (A)</p> Signup and view all the answers

What is the role of ATP synthase in the process of oxidative phosphorylation?

<p>To synthesize ATP from ADP and inorganic phosphate (C)</p> Signup and view all the answers

Which of the following is NOT a component of the electron transport chain in cellular respiration?

<p>ATP synthase (A)</p> Signup and view all the answers

What is the role of CoA in the citric acid cycle?

<p>It is used to carry acetyl groups (D)</p> Signup and view all the answers

How many ATP molecules are produced by the ETC from the oxidation of one molecule of NADH?

<p>3 (D)</p> Signup and view all the answers

How many molecules of CO2 are produced per glucose molecule during the complete oxidation of glucose?

<p>6 (A)</p> Signup and view all the answers

Which of the following molecules is directly involved in the production of ATP through oxidative phosphorylation?

<p>NADH (D)</p> Signup and view all the answers

What is the final electron acceptor in the electron transport chain?

<p>Oxygen (B)</p> Signup and view all the answers

Which molecule is directly regenerated by the reduction of NAD+?

<p>Oxaloacetate (A)</p> Signup and view all the answers

Which enzyme catalyzes the conversion of malate to oxaloacetate?

<p>Malate dehydrogenase (D)</p> Signup and view all the answers

Which molecule is directly produced from the decarboxylation of α-ketoglutarate?

<p>Succinyl CoA (B)</p> Signup and view all the answers

Where in the cell does the citric acid cycle occur?

<p>Mitochondrial matrix (A)</p> Signup and view all the answers

Which molecule directly donates electrons to the electron transport chain?

<p>Both B and C (C)</p> Signup and view all the answers

Which molecule is a key intermediate in both glycolysis and the citric acid cycle?

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

From which substrate does the citric acid cycle begin?

<p>Acetyl CoA (B)</p> Signup and view all the answers

Which molecule is a substrate for the enzyme succinate dehydrogenase?

<p>Succinate (D)</p> Signup and view all the answers

Which molecule is directly produced when citrate is isomerized?

<p>Isocitrate (D)</p> Signup and view all the answers

Which of the following molecules is a product of the citric acid cycle?

<p>ATP (C)</p> Signup and view all the answers

Which molecule is directly involved in the conversion of succinyl CoA to succinate?

<p>GDP (B)</p> Signup and view all the answers

What is the net gain of ATP molecules per glucose molecule that is completely oxidized through glycolysis and the citric acid cycle?

<p>36 (D)</p> Signup and view all the answers

Which molecule acts as an electron acceptor in the reaction catalyzed by succinate dehydrogenase?

<p>FAD (C)</p> Signup and view all the answers

What are the major products of the citric acid cycle that contribute to ATP production?

<p>NADH, FADH2, and ATP (C)</p> Signup and view all the answers

Which of the following is NOT a direct product of the citric acid cycle?

<p>Acetyl CoA (D)</p> Signup and view all the answers

Which molecule acts as a key regulator of the citric acid cycle?

<p>All of the above (D)</p> Signup and view all the answers

Flashcards

Citrate

A compound that loses a CH2 and CO2 during the reaction.

Isocitrate

The compound formed after citrate loses a CH2 and CO2 and is oxidized to reduce NAD+.

NAD+

A coenzyme that is reduced to NADH during the metabolism of isocitrate.

α-Ketoglutarate

The compound that results after isocitrate undergoes oxidation and loses another CO2.

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Dehydrogenase

Enzymes that facilitate the oxidation of substrates while reducing NAD+ to NADH.

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Acetyl CoA

A molecule that donates a two-carbon acetyl group to metabolic reactions.

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Citrate Synthase

An enzyme that catalyzes the reaction between Acetyl CoA and oxaloacetate to form citrate.

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Oxaloacetate

A four-carbon molecule that combines with Acetyl CoA to initiate the citric acid cycle.

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Citric Acid Cycle

A series of enzymatic reactions that produce energy through the oxidation of Acetyl CoA.

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Krebs Cycle

A series of 8 enzyme-catalyzed reactions crucial for energy production.

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FADH2

Another electron carrier produced in the Krebs cycle, also used in the ETC.

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ATP

Energy currency of the cell, produced in glycolysis and Krebs cycle.

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Glycolysis

The first step of cellular respiration that breaks down glucose to pyruvate.

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Electron Transport Chain

Final stage of cellular respiration where NADH and FADH2 are used to produce ATP.

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Decarboxylation

The process of removing a carbon atom from a molecule, producing CO2.

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Oxidation of Pyruvate

The conversion of pyruvate to acetyl CoA before entering the Krebs cycle.

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Fermentation

Alternate process for energy production when oxygen is absent, breaking down glucose.

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Electron Transport Chain (ETC)

A series of proteins that transfer electrons, generating ATP through oxidative phosphorylation.

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ATP Production from NADH

Each NADH results in the production of approximately 3 ATP during the ETC.

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ATP Production from FADH2

Each FADH2 results in about 2 ATP when it donates electrons to the ETC.

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Chemiosmosis

Process of synthesizing ATP using the energy from a proton gradient established by the ETC.

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Proton Gradient

A difference in H+ ion concentration across a membrane, used to generate ATP.

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ATP Synthase

An enzyme that synthesizes ATP from ADP and Pi using the energy of the proton gradient.

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Malate Dehydrogenase

An enzyme that oxidizes malate to oxaloacetate, reducing NAD+ to NADH.

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Oxidative Phosphorylation

The process where NADH and FADH2 are oxidized in the electron transport chain to generate ATP.

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Overall Stoichiometry

The balanced equation representing the total inputs and outputs of the citric acid cycle.

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Acetyl-CoA Inputs

The reactants in the citric acid cycle including Acetyl-CoA, NAD+, FAD, GDP, Pi, and H2O.

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NADH Production

Generated during the oxidation of substrates in the citric acid cycle, crucial for ATP production.

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FADH2 Role

An electron carrier produced in the citric acid cycle that enters the electron transport chain.

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GTP Formation

A molecule formed during the citric acid cycle, similar to ATP and used in energy transfer.

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Carbon Dioxide Outputs

The byproducts of the citric acid cycle, released for every acetyl unit oxidized.

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Malate

A four-carbon compound formed from the reduction of oxaloacetate.

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Fumarate

A four-carbon compound formed in the citric acid cycle.

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Succinate

A four-carbon compound that is oxidized to form fumarate.

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Succinyl CoA

A four-carbon intermediate formed during the citric acid cycle.

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Coenzyme A (CoA)

A helper molecule that transports acetate into the citric acid cycle.

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Alpha-ketoglutarate

A five-carbon compound formed after isocitrate loses CO2.

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Study Notes

Cellular Respiration

  • Cellular respiration is the process of harvesting energy from glucose in the presence of oxygen.

Stages of Cellular Respiration

  • Glycolysis: Glucose is broken down into two pyruvate molecules, producing a net gain of 2 ATP molecules and 2 NADH. This occurs in the cytoplasm.

  • Oxidation of Pyruvate (Link Reaction): Pyruvate is transported into the mitochondria, decarboxylated (CO2 is removed), and combined with coenzyme A to form acetyl CoA. Two NADH molecules are also produced.

  • Krebs Cycle (Citric Acid Cycle): Acetyl CoA enters the Krebs cycle, where it is further oxidized, producing 2 ATP, 6 NADH and 2 FADH2. The cycle also releases 4 CO2. This takes place within the mitochondrial matrix.

  • Electron Transport Chain (ETC): High-energy electrons from NADH and FADH2 are passed down a chain of protein complexes. This process pumps H+ ions into the intermembrane space, creating a proton gradient. Oxygen is the final electron acceptor, combining with H+ ions to form water. ATP is synthesized via chemiosmosis (proton gradient provides energy) to create the bulk of the ATP produced during cellular respiration. This stage occurs in the inner mitochondrial membrane.

Fermentation

  • Fermentation is an anaerobic process that occurs when oxygen is not available. It involves the breakdown of glucose, but produces fewer ATP molecules compared to aerobic respiration.

  • Alcoholic Fermentation: Pyruvate is converted into ethanol and carbon dioxide, regenerating NAD+. Examples include baking and winemaking.

  • Lactic Acid Fermentation: Pyruvate is converted into lactic acid (lactate), regenerating NAD+. This is common in muscle cells during intense exercise.

ATP Production Summary

  • The overall process of aerobic cellular respiration generates a net yield of 38 ATP molecules.

  • The exact number can vary slightly based on cell type and transport mechanisms.

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