Biology

Cellular Respiration and Enzymes

1,721 Questions

Explore key concepts of cellular respiration, including glycolysis, the Krebs cycle, and the electron transport chain. These questions also cover ATP production, anaerobic respiration, and essential metabolic pathways. This topic forms a core part of the biology syllabus for many competitive examinations.

Glycolysis and metabolic pathwaysKrebs cycle processesElectron transport chainATP production countAnaerobic respiration products

Cellular Respiration and Enzymes Questions

Multiple choice

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
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

Multiple choice

How many stages make up the Krebs Cycle?

  1. 6

  2. 8

  3. 10

  4. 12
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

Multiple choice

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

  1. Acetyl CoA

  2. Glucose

  3. Pyruvate

  4. Citrate
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

Multiple choice

What is the final product of the Krebs Cycle?

  1. Oxaloacetate

  2. Malate

  3. Fumarate

  4. Succinate
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

Multiple choice

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
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

Multiple choice

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
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

Multiple choice

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
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

Multiple choice

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

  1. 2

  2. 4

  3. 6

  4. 8
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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

Multiple choice

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

  1. Acetyl CoA

  2. Isocitrate

  3. FADH2

  4. Succinyl CoA
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

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

Multiple choice

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
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

Multiple choice

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
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

Multiple choice

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
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

Multiple choice

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

  1. Acetyl CoA

  2. Fumarate

  3. Malate

  4. Oxaloacetate
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

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

Multiple choice

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

  1. 2

  2. 4

  3. 6

  4. 8
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

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

Multiple choice

Which of the following is NOT a mechanism of drug metabolism?

  1. Phase I reactions

  2. Phase II reactions

  3. Excretion

  4. Biotransformation
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Excretion is the process of eliminating drugs and their metabolites from the body, not a mechanism of drug metabolism.