Krebs Cycle: The Powerhouse of Cellular Respiration

Question 1

What enzyme kickstarts the Krebs cycle by combining acetyl-CoA and oxaloacetate to form citrate?

Accepted Answer

Citrate synthase

Answer

Fumarase

Answer

Succinate dehydrogenase

Answer

Isocitrate dehydrogenase

Question 2

Which enzyme in the Krebs cycle catalyzes the removal of a carbon dioxide molecule from isocitrate, resulting in the formation of alpha-ketoglutarate?

Accepted Answer

Isocitrate dehydrogenase

Answer

Citrate synthase

Answer

Succinate dehydrogenase

Question 3

What is the primary role of the Krebs cycle in cellular respiration?

Accepted Answer

Providing NADH and FADH2 to the electron transport chain for ATP production

Answer

Directly generating a significant amount of ATP

Answer

Occurring in the cytoplasm and solely using NADH as an electron carrier

Answer

Releasing carbon dioxide as a waste product, concluding cellular respiration

Question 4

Which reaction initiates the Krebs cycle?

Accepted Answer

Condensation of oxaloacetate with acetyl-CoA

Answer

Isomerization of citrate to isocitrate

Answer

Dehydrogenation of succinate to fumarate

Answer

Hydration of fumarate to malate

Question 5

Isocitrate dehydrogenase catalyzes which reaction in the Krebs cycle?

Accepted Answer

Oxidation of isocitrate to α-ketoglutarate

Answer

Conversion of citrate to isocitrate

Answer

Decarboxylation of α-ketoglutarate to succinyl-CoA

Answer

Conversion of succinyl-CoA to succinate

Question 6

What is the primary function of NADH and FADH2 in the Krebs cycle?

Accepted Answer

Electron carriers for the electron transport chain

Answer

Substrates for ATP synthesis

Answer

Regulators of enzyme activity

Answer

Coenzymes for substrate binding

Question 7

Which molecule is NOT a direct product of the Krebs cycle?

Accepted Answer

Acetyl-CoA

Answer

ATP

Answer

NADH

Answer

FADH2

Question 8

In which cellular compartment does the Krebs cycle occur?

Accepted Answer

Mitochondrial matrix

Answer

Nucleus

Answer

Cytoplasm

Answer

Endoplasmic reticulum

Question 9

What is the central importance of the Krebs cycle in cellular metabolism?

Accepted Answer

Generation of energy through ATP production

Answer

Provision of building blocks for macromolecules

Answer

Detoxification of harmful substances

Answer

Storage of genetic information

Question 10

Which enzyme catalyzes the initial step of the Krebs cycle, converting citrate to isocitrate?

Accepted Answer

Citrate synthase

Answer

Aconitase

Answer

Isocitrate dehydrogenase

Answer

α-Ketoglutarate dehydrogenase

Question 11

Which intermediate of the Krebs cycle directly enters the electron transport chain?

Accepted Answer

Succinate

Answer

Malate

Answer

Fumarate

Answer

Citrate

Question 12

In which cellular compartment does the Krebs cycle take place?

Accepted Answer

Mitochondrial matrix

Answer

Cytoplasm

Answer

Nucleus

Answer

Golgi apparatus

Question 13

Which enzyme is responsible for the oxidative decarboxylation of α-ketoglutarate to succinyl-CoA?

Accepted Answer

α-Ketoglutarate dehydrogenase

Answer

Citrate synthase

Answer

Isocitrate dehydrogenase

Answer

Succinyl-CoA synthetase

Question 14

To determine the rate of NADH production in the Krebs cycle, which experimental technique is most appropriate?

Accepted Answer

Spectrophotometry (measuring NADH absorbance at 340 nm)

Answer

Fluorometry (measuring NADH fluorescence)

Answer

Mass spectrometry (measuring NADH mass)

Answer

pH measurement (measuring reaction mixture pH)

Question 15

Examine the unique mechanisms of aconitase and fumarase in the Krebs cycle. Discuss their stereospecificity and the roles of iron-sulfur clusters in their catalytic functions.

Accepted Answer

Both aconitase and fumarase exhibit stereospecificity and utilize iron-sulfur clusters in their mechanisms.

Answer

Aconitase is stereospecific, while fumarase is not. Both enzymes utilize iron-sulfur clusters.

Answer

Aconitase utilizes iron-sulfur clusters, while fumarase does not. Both enzymes are stereospecific.

Answer

Neither enzyme exhibits stereospecificity, and they do not utilize iron-sulfur clusters.

Question 16

In the conversion of succinyl-CoA to succinate, what is the main function of GTP hydrolysis?

Accepted Answer

Provides energy for the reaction

Answer

Produces NADH

Answer

Releases CO2

Answer

Inhibits succinyl-CoA synthetase

Question 17

Which molecule initiates the citric acid cycle?

Accepted Answer

Acetyl-CoA

Answer

Pyruvate (converts to Acetyl-CoA)

Answer

Oxaloacetate (combines with Acetyl-CoA)

Answer

Glucose

Question 18

Which enzyme catalyzes the isomerization of citrate to isocitrate in the citric acid cycle?

Accepted Answer

Aconitase

Answer

Succinate dehydrogenase (oxidizes succinate to fumarate)

Answer

Citrate synthase (condenses Acetyl-CoA with oxaloacetate)

Answer

Alpha-ketoglutarate dehydrogenase (converts alpha-ketoglutarate to succinyl-CoA)

Question 19

Which intermediate of the citric acid cycle has a four-carbon structure?

Accepted Answer

Succinate

Answer

Citrate (has six carbons)

Answer

Oxaloacetate (has four carbons, but regenerates and doesn't get consumed)

Answer

Isocitrate (has six carbons)

Question 20

What is the primary function of NADH and FADH2 produced in the citric acid cycle?

Accepted Answer

Electron carriers

Answer

Energy storage molecules

Answer

Substrate-level phosphorylation

Answer

Coenzymes for enzymatic reactions

Question 21

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

Accepted Answer

Carbon dioxide

Answer

Pyruvate (converts to Acetyl-CoA before entering the cycle)

Answer

Glycerol (not produced in the citric acid cycle)

Question 22

What is the main function of the citric acid cycle?

Accepted Answer

Generates electron carriers, carbon dioxide, and precursors for other metabolic pathways

Answer

Breaks down glucose completely into carbon dioxide and water

Answer

Produces most of the ATP in cellular respiration (occurs in oxidative phosphorylation)

Question 23

Which disease results from a deficiency in an enzyme of the citric acid cycle?

Accepted Answer

Leigh syndrome

Answer

Sickle cell anemia (hemoglobin disorder)

Answer

Huntington's disease (neurodegenerative disorder)

Answer

Phenylketonuria (amino acid metabolism disorder)