Pyruvate Dehydrogenase Complex Quiz

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Questions and Answers

The reaction of pyruvate dehydrogenase, forming acetyl-CoA, is reversible.

False (B)

The enzyme to reverse the reaction catalyzed by pyruvate dehydrogenase (forming pyruvate from Acetyl-CoA) has been identified in humans.

False (B)

Acetyl-CoA can be used as a substrate for gluconeogenesis.

False (B)

Fatty acids with an odd number of carbon atoms yield acetyl-CoA as the final product of β-oxidation.

<p>False (B)</p> Signup and view all the answers

Lactate produced in anaerobic glycolysis can be used as a substrate for gluconeogenesis.

<p>True (A)</p> Signup and view all the answers

Amino acids that give rise to acetyl-CoA are referred to as glucogenic.

<p>False (B)</p> Signup and view all the answers

What is the fate of acetyl-CoA derived from substrates that yield it?

<p>Enters the citric acid cycle (B)</p> Signup and view all the answers

Which of the following can be a substrate for gluconeogenesis?

<p>Propionyl-CoA from odd-number fatty acids (C)</p> Signup and view all the answers

What is the key reason why acetyl-CoA cannot be used as a substrate for gluconeogenesis?

<p>Enters the citric acid cycle irreversibly (B)</p> Signup and view all the answers

Which substrates can potentially be used as a substrate for gluconeogenesis?

<p>Propionyl-CoA (B)</p> Signup and view all the answers

What product is yielded by fatty acids with an odd number of carbon atoms in the final cycle of beta-oxidation?

<p>Propionyl-CoA (3C) (B)</p> Signup and view all the answers

What makes an amino acid ketogenic?

<p>Yields acetyl-CoA (B)</p> Signup and view all the answers

Flashcards

Pyruvate Dehydrogenase Reaction: Reversible?

The pyruvate dehydrogenase reaction, which forms acetyl-CoA, is irreversible.

Reversal enzyme of Pyruvate Dehydrogenase in humans?

No, the enzyme to reverse the reaction catalyzed by pyruvate dehydrogenase (forming pyruvate from Acetyl-CoA) hasn't been identified in humans.

Acetyl-CoA for Gluconeogenesis?

No, acetyl-CoA cannot be directly converted into glucose via gluconeogenesis.

Odd-chain fatty acids final product.

False, fatty acids with an odd number of carbon atoms yield propionyl-CoA, not acetyl-CoA, in the final beta-oxidation cycle.

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Lactate for Gluconeogenesis?

True, lactate can be converted back into glucose via the Cori cycle.

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Ketogenic Amino Acids

These amino acids yield ketone bodies or fatty acids.

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Fate of Acetyl-CoA

It enters the citric acid cycle for oxidation.

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Gluconeogenesis Substrate

Propionyl-CoA, which can be converted to succinyl-CoA.

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Why Acetyl-CoA Can't Be Used for Gluconeogenesis

The entry into the citric acid cycle is essentially irreversible, leading to the loss of carbon atoms as CO2, preventing net synthesis of glucose.

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Odd Number Fatty Acids Produce?

Yields propionyl-CoA (3C).

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Ketogenic Amino Acid Defined

An amino acid that yields acetyl-CoA or acetoacetyl-CoA during its catabolism, contributing to ketone body formation.

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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.

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