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The Krebs Cycle: The Central Hub of Energy Metabolism

Description: The Krebs Cycle Quiz: Test Your Understanding of the Central Hub of Energy Metabolism
Number of Questions: 14
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Tags: krebs cycle citric acid cycle energy metabolism biochemistry
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What is the primary role of the Krebs Cycle in cellular metabolism?

  1. Generation of ATP

  2. Synthesis of amino acids

  3. Production of NADH and FADH2

  4. Breakdown of glucose


Correct Option: C
Explanation:

The Krebs Cycle, also known as the Citric Acid Cycle, is primarily responsible for generating NADH and FADH2, which are high-energy electron carriers used in the electron transport chain for ATP production.

How many stages make up the Krebs Cycle?

  1. 6

  2. 8

  3. 10

  4. 12


Correct Option: B
Explanation:

The Krebs Cycle consists of eight distinct stages, each involving specific enzymatic reactions that transform various intermediates.

Which molecule serves as the initial substrate for the Krebs Cycle?

  1. Acetyl CoA

  2. Glucose

  3. Pyruvate

  4. Citrate


Correct Option: A
Explanation:

Acetyl CoA is the starting molecule for the Krebs Cycle, derived from the breakdown of carbohydrates, fats, and proteins during cellular respiration.

What is the final product of the Krebs Cycle?

  1. Oxaloacetate

  2. Malate

  3. Fumarate

  4. Succinate


Correct Option: A
Explanation:

The Krebs Cycle completes a full cycle when oxaloacetate, the final product, is regenerated, ready to accept another acetyl CoA molecule and initiate the cycle again.

Which enzyme catalyzes the conversion of citrate to isocitrate in the Krebs Cycle?

  1. Aconitase

  2. Isocitrate dehydrogenase

  3. α-Ketoglutarate dehydrogenase

  4. Succinate dehydrogenase


Correct Option: A
Explanation:

Aconitase is the enzyme responsible for the isomerization of citrate to isocitrate, a crucial step in the Krebs Cycle.

What is the name of the enzyme complex that catalyzes the oxidative decarboxylation of α-ketoglutarate to succinyl CoA?

  1. Pyruvate dehydrogenase complex

  2. α-Ketoglutarate dehydrogenase complex

  3. Succinate dehydrogenase complex

  4. Citrate synthase


Correct Option: B
Explanation:

The α-Ketoglutarate dehydrogenase complex is the enzyme responsible for the conversion of α-ketoglutarate to succinyl CoA, releasing carbon dioxide as a byproduct.

Which step in the Krebs Cycle involves the substrate-level phosphorylation of GDP to GTP?

  1. Conversion of succinyl CoA to succinate

  2. Conversion of isocitrate to α-ketoglutarate

  3. Conversion of malate to oxaloacetate

  4. Conversion of citrate to isocitrate


Correct Option: A
Explanation:

The conversion of succinyl CoA to succinate is coupled with the substrate-level phosphorylation of GDP to GTP, generating a high-energy GTP molecule.

How many molecules of NADH are produced per glucose molecule during the Krebs Cycle?

  1. 2

  2. 4

  3. 6

  4. 8


Correct Option: C
Explanation:

During the complete oxidation of one glucose molecule through the Krebs Cycle, a total of six molecules of NADH are produced.

Which intermediate in the Krebs Cycle is directly involved in the electron transport chain?

  1. Acetyl CoA

  2. Isocitrate

  3. FADH2

  4. Succinyl CoA


Correct Option: C
Explanation:

FADH2, generated during the oxidation of succinate to fumarate, directly participates in the electron transport chain, transferring electrons to the ubiquinone pool.

What is the role of oxaloacetate in the Krebs Cycle?

  1. Acceptor of acetyl CoA

  2. Electron carrier

  3. Regulator of cycle activity

  4. Final product of the cycle


Correct Option: A
Explanation:

Oxaloacetate serves as the acceptor of acetyl CoA, initiating the Krebs Cycle and allowing for the continuous oxidation of acetyl groups.

Which enzyme catalyzes the conversion of malate to oxaloacetate in the Krebs Cycle?

  1. Malate dehydrogenase

  2. Isocitrate dehydrogenase

  3. Succinate dehydrogenase

  4. α-Ketoglutarate dehydrogenase


Correct Option: A
Explanation:

Malate dehydrogenase is the enzyme responsible for the reversible conversion of malate to oxaloacetate, a crucial step in the Krebs Cycle.

What is the name of the enzyme that catalyzes the decarboxylation of citrate to form α-ketoglutarate?

  1. Aconitase

  2. Isocitrate dehydrogenase

  3. α-Ketoglutarate dehydrogenase

  4. Succinate dehydrogenase


Correct Option: B
Explanation:

Isocitrate dehydrogenase catalyzes the oxidative decarboxylation of isocitrate to form α-ketoglutarate, releasing carbon dioxide as a byproduct.

Which intermediate in the Krebs Cycle is directly involved in the urea cycle?

  1. Acetyl CoA

  2. Fumarate

  3. Malate

  4. Oxaloacetate


Correct Option: B
Explanation:

Fumarate is an intermediate in the Krebs Cycle that is also involved in the urea cycle, where it is converted to argininosuccinate.

What is the overall yield of ATP molecules generated per glucose molecule during the Krebs Cycle?

  1. 2

  2. 4

  3. 6

  4. 8


Correct Option: A
Explanation:

The Krebs Cycle directly generates two molecules of ATP per glucose molecule through substrate-level phosphorylation.

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