30 Questions
What is the primary role of the citric acid cycle in metabolism?
To generate energy through the oxidation of carbohydrates, lipids, and proteins
Which of the following enzymes catalyzes an irreversible reaction that produces substrates for gluconeogenesis?
Pyruvate Carboxylase
How does pyruvate enter the mitochondria?
It diffuses through the outer mitochondrial membrane and is transported into the matrix by an H+-coupled symporter
What is the primary function of the pyruvate dehydrogenase complex?
To convert pyruvate to acetyl-CoA, which can then enter the citric acid cycle
What is the role of pyruvate carboxylase in gluconeogenesis?
It catalyzes the irreversible carboxylation of pyruvate to oxaloacetate, providing a substrate for gluconeogenesis
What is the relationship between the citric acid cycle and gluconeogenesis?
The citric acid cycle provides intermediates that can be used for gluconeogenesis
What role does oxaloacetate play in the citric acid cycle?
Acting as a catalyst and being regenerated at the end of the cycle
Where are the enzymes of the citric acid cycle located?
Mitochondrial matrix
Which enzyme connects the citric acid cycle to the Electron Transport Chain (ETC)?
Succinate dehydrogenase
What happens when the withdrawal of cycle intermediates for biosynthesis lowers their concentrations?
Cycle intermediates are replenished by anaplerotic reactions
What is the most important anaplerotic reaction in mammalian liver?
Reversible carboxylation of pyruvate to form oxaloacetate
What is the primary function of pyruvate carboxylase in cellular metabolism?
Catalyzing the carboxylation of pyruvate to form oxaloacetate
Which of the following is the most accurate description of the second stage of respiration?
The acetyl groups are oxidized to CO2 in the citric acid cycle.
What is the primary purpose of the electron transfer in the third stage of respiration?
To conserve energy in the form of ATP
Which of the following is NOT a mechanism of control in the TCA cycle?
Covalent modifications
Which of the following enzymes in the citric acid cycle is NOT regulated by covalent modifications?
All of the above
What is the main reason the citric acid cycle is active in both the fasted and fed states?
The citric acid cycle is an amphibolic process that includes both anabolic and catabolic reactions.
Which of the following is NOT a regulator enzyme of the citric acid cycle?
Malate dehydrogenase
What is the role of acetyl-CoA in the regulation of pyruvate carboxylase and pyruvate dehydrogenase?
Acetyl-CoA acts as an allosteric activator of pyruvate carboxylase and an inhibitor of pyruvate dehydrogenase.
What is the purpose of the anaplerotic reaction catalyzed by pyruvate carboxylase?
To produce substrates for gluconeogenesis.
What is the role of the pyruvate dehydrogenase complex?
To catalyze the conversion of pyruvate to acetyl-CoA, which can then be used in the citric acid cycle or for lipogenesis.
What is the significance of the location of pyruvate dehydrogenase and pyruvate carboxylase within the cell?
Both pyruvate dehydrogenase and pyruvate carboxylase are located in the mitochondria.
What is the role of the cofactors required for the activity of the pyruvate dehydrogenase complex?
The cofactors are necessary for the catalytic activity of the complex.
How does the phosphorylation state of the pyruvate dehydrogenase complex affect its activity?
Phosphorylation of the complex inhibits its activity, while dephosphorylation activates it.
What is the most important negative allosteric effector for the pyruvate dehydrogenase complex (PDH)?
Acetyl-CoA
Which of the following cofactors is NOT required for the activity of the pyruvate dehydrogenase complex?
ATP
What is the fate of acetyl-CoA produced by the pyruvate dehydrogenase complex?
It enters the citric acid cycle
Which of the following statements about the pyruvate dehydrogenase complex (PDH) is correct?
It is an allosteric enzyme that works in one direction
Which of the following substrates can be used for gluconeogenesis?
Odd-numbered fatty acids and glycerol
What is the role of insulin in the regulation of the pyruvate dehydrogenase complex (PDH)?
Insulin activates PDH by dephosphorylation
Test your knowledge on the citric acid cycle as the final common pathway for carbohydrate, lipid, and protein oxidation, along with the entrance of pyruvate into mitochondria. Explore its role in various metabolic processes like gluconeogenesis, lipogenesis, and amino acid interconversion.
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