24 Questions
What is another name for the citric acid cycle?
Tricarboxylic acid cycle
Where does the citric acid cycle occur in the cell?
Mitochondria
Which molecule is the major source of acetyl CoA for the citric acid cycle?
Pyruvate
What is the final electron acceptor in the citric acid cycle?
Oxygen (O2)
Which of the following is converted to CO2 in the citric acid cycle?
Carbon skeletons of carbohydrates, amino acids, and fatty acids
What is the overall importance of the citric acid cycle in metabolism?
Oxidative catabolism of carbohydrates, amino acids, and fatty acids
What is the role of the pyruvate dehydrogenase complex (PDH complex)?
To convert pyruvate to acetyl CoA in the mitochondria
Which coenzyme is required for the enzyme pyruvate carboxylase (E1) in the PDH complex?
Thiamine pyrophosphate (TPP)
What is the role of citrate synthase in the citric acid cycle?
To catalyze the condensation of acetyl CoA and oxaloacetate to form citrate
Which statement about aconitase is correct?
It isomerizes citrate to isocitrate
What is the primary means of regulation for citrate synthase?
Substrate availability
Which of the following is NOT a coenzyme required by the PDH complex?
Adenosine triphosphate (ATP)
What is the role of aconitase in the TCA cycle?
Aconitase is inhibited by the plant toxin fluoroacetate.
What is the role of isocitrate dehydrogenase in the TCA cycle?
Isocitrate dehydrogenase catalyzes the irreversible oxidative decarboxylation of isocitrate.
What is the role of the α-ketoglutarate dehydrogenase complex in the TCA cycle?
The α-ketoglutarate dehydrogenase complex is inhibited by its products, NADH and succinyl CoA.
What is the role of succinate thiokinase in the TCA cycle?
Succinate thiokinase is a substrate-level phosphorylation reaction in the TCA cycle.
What is the role of succinate dehydrogenase in the TCA cycle?
Succinate dehydrogenase catalyzes the oxidation of succinate to fumarate.
Which statement about the TCA cycle is true?
The TCA cycle releases three CO2 molecules.
What is the role of fumarase in the citric acid cycle?
It catalyzes the hydration of fumarate to malate
How many pairs of electrons are transferred during one turn of the citric acid cycle?
Four pairs, three reducing $NAD^+$ and one reducing $FAD$
What is the primary factor that regulates the citric acid cycle?
The supply of oxidized cofactors ($NAD^+$ and $FAD$)
Which of the following enzymes is NOT mentioned as being important for the regulation of the citric acid cycle?
Malate dehydrogenase
What is the fate of the two carbon atoms that enter the citric acid cycle as acetyl-CoA?
They are released as $CO_2$
What is the primary factor that determines the rate of ATP utilization, which in turn regulates the citric acid cycle?
The rate of chemical and physical work in the cell
Learn about the reactions, importance, and regulation of the citric acid cycle in this quiz prepared by Dr. Shymaa Ahmed Maher and presented by Dr. Nora Hosny Ahmed. Understand how the cycle contributes to the production of reducing equivalents and serves as a pathway for both catabolism and synthesis of amino acids and fatty acids.
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