12 Questions
The reaction of pyruvate dehydrogenase, forming acetyl-CoA, is reversible.
False
The enzyme to reverse the reaction catalyzed by pyruvate dehydrogenase (forming pyruvate from Acetyl-CoA) has been identified in humans.
False
Acetyl-CoA can be used as a substrate for gluconeogenesis.
False
Fatty acids with an odd number of carbon atoms yield acetyl-CoA as the final product of β-oxidation.
False
Lactate produced in anaerobic glycolysis can be used as a substrate for gluconeogenesis.
True
Amino acids that give rise to acetyl-CoA are referred to as glucogenic.
False
What is the fate of acetyl-CoA derived from substrates that yield it?
Enters the citric acid cycle
Which of the following can be a substrate for gluconeogenesis?
Propionyl-CoA from odd-number fatty acids
What is the key reason why acetyl-CoA cannot be used as a substrate for gluconeogenesis?
Enters the citric acid cycle irreversibly
Which substrates can potentially be used as a substrate for gluconeogenesis?
Propionyl-CoA
What product is yielded by fatty acids with an odd number of carbon atoms in the final cycle of beta-oxidation?
Propionyl-CoA (3C)
What makes an amino acid ketogenic?
Yields acetyl-CoA
Study Notes
Pyruvate Oxidation
- Pyruvate in the mitochondrial matrix is oxidized to acetyl-CoA and CO2 by the pyruvate dehydrogenase (PDH) complex, producing NADH+H.
Irreversible Reaction
- The reaction of pyruvate dehydrogenase, forming acetyl-CoA, is irreversible and requires an allosteric enzyme.
- Allosteric enzymes only work in one direction, and an opposite allosteric enzyme is needed to reverse the reaction.
Gluconeogenesis
- Substrates degraded into acetyl-CoA (e.g. even-number fatty acids, lysine, leucine) cannot be used as a substrate for gluconeogenesis.
- However, substrates yielding propionyl-CoA (e.g. fatty acids with an odd number of carbon atoms) or glycerol (3C) can be used as a substrate for gluconeogenesis.
- Lactate (3C) produced in anaerobic glycolysis can also be a substrate for gluconeogenesis.
Ketogenic Amino Acids
- Amino acids that give rise to acetyl-CoA are referred to as ketogenic.
Test your knowledge on the conversion of pyruvate to acetyl-CoA by the pyruvate dehydrogenase (PDH) complex in the mitochondrial matrix. Understand the irreversibility of this reaction and the role of allosteric enzymes in the process.
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