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Regulation of Pyruvate Dehydrogenase Flashcards

(20 cards)

1
Q

True or false: The conversion of pyruvate to acetyl CoA by pyruvate dehydrogenase is reversible.

A

False; it is irreversible.

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2
Q

Which compounds are competitive inhibitors of pyruvate dehydrogenase?

A

NADH and acetyl-CoA (the products of the reaction)

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3
Q

True or false: NAD+ is a competitive inhibitor of pyruvate dehydrogenase.

A

False; NADH is a competitive inhibitor (competes for NAD+ binding site)

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4
Q

True or false: Acetyl-CoA is a competitive inhibitor of pyruvate dehydrogenase.

A

True

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5
Q

What two molecules actually drive the E2 and E3 reactions of pyruvate dehydrogenase in reverse?

A

NADH and acetyl-CoA

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6
Q

What is the effect of high ratios of [NADH]/[NAD+] and [acetyl-CoA]/[CoA]?

A

Maintains E2 in acetylated form, making it incapable of accepting hydroxyethyl group from TTP

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7
Q

Which part of pyruvate dehydrogenase reaction is inhibited by NADH?

A

The dihydrolipoyl dehydrogenase (E3).

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8
Q

Which part of pyruvate dehydrogenase reaction is inhibited by acetyl-CoA?

A

The transacetylase component (E2), because acetyl-CoA binds to it.

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9
Q

To what fate does the oxidative carboxylation of pyruvate to acetyl-CoA commit the carbon atoms derived from glucose?

A

Either oxidation to CO2 by the TCA cycle and generation of energy or incorporation into lipid (because acetyl-CoA is a precursor for lipid synthesis).

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10
Q

What are the two key means of regulating pyruvate dehydrogenase?

A

1) Competitive inhibition by NADH and acetyl CoA

2) Covalent modification of E1 by pyruvate dehydrogenase kinase that inactivates the enzyme.

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11
Q

Which hormone reverses the inactivation of pyruvate dehydrogenase kinase by activating pyruvate dehydrogenase phosphatase?

A

Insulin

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12
Q

What activates pyruvate dehydrogenase kinase?

A

NADH and acetyl-CoA

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13
Q

When activated, what does pyruvate dehydrogenase kinase do to pyruvate dehydrogenase?

A

It causes phosphorylation that inactivates the multi-enzyme complex.

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14
Q

Which enzyme, when activated by insulin, reverses the effects of pyruvate dehydrogenase kinase? How does it do this?

A

Pyruvate dehydrogenase phosphatase; it removes phosphoryl groups, reactivating pyruvate dehydrogenase and allowing the TCA Cycle to continue.

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15
Q

What causes insulin to promote the synthesis of acetyl-CoA and glycogen?

A

Increased [glucose].

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16
Q

True or false: the phosphorylated E1 enzyme is active.

A

False; the dephosphorylated E1 enzyme is active.

17
Q

What causes the deactivation of the E1 enzyme?

A

Phosphorylation by pyruvate dehydrogenase kinase, which is activated by increase concentrations of NADH and Acetyl-CoA

18
Q

What inhibits pyruvate dehydrogenase kinase?

A

Pyruvate, ADP, and Ca+

19
Q

True or false: pyruvate dehydrogenase is activated by cAMP.

A

False; it is unaffected by cAMP.

20
Q

True or false: Ca2+ (released in response to hormones) activates pyruvate dehydrogenase kinase and inhibits pyruvate dehydrogenase phosphatase.

A

False; Ca2+ inhibits pyruvate dehydrogenase kinase and activates pyruvate dehydrogenase phosphatase.