Unit 7 Pt. 1 (PD Complex) Flashcards

(27 cards)

1
Q

What converts pyruvate to acetyl-CoA?

A

Pyruvate dehydrogenase complex (PDH complex)

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2
Q

Where in the cell is the PDH complex located?

A

In the mitochondrial matrix

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3
Q

What is the overall reaction of the PDH complex?

A

Pyruvate is decarboxylated (and oxidized) into acetate, followed by the formation of acetyl-CoA (a thioester)

*note that free acetate never actually forms

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4
Q

What is E1 of the PDH?

A

Pyruvate dehydrogenase

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5
Q

What is e2 of PDH?

A

Dihydrolipoyltransacetylase

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6
Q

What is E3 of the PDH?

A

dihydrolipoyldehydrogenase

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7
Q

What are the cofactors involved with the PDH complex and where are they found?

A

Thiamine pyrophosphate (TPP) - bound to E1

Lipoamide/lipolysine - bound to E2

FAD - Bound to E3

NAD+ - Free

CoA(SH) - Free

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8
Q

What molecules make up Coenzyme A?

A

ADP, Vitamin B5 (pantothenate) and ß-mercaptoethylamine

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9
Q

What is the function of acetyl-CoA?

A

Carries the acyl group by forming a high energy thioester bond. “Primes” acetate for metabolism.

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10
Q

What is TPP?

A

Thiamin pyrophosphate

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11
Q

What is thiamin pyrophosphate derived from?

A

Derived from vitamin B1 (Thiamine)

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12
Q

What is special about TPP?

A

It can easily form a reactive carbanion

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13
Q

What is this molecule?

A
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14
Q

What is this molecule?

A

Coenzyme A

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15
Q

What is lipoic aside attached to?

A

It is attached to a lysine side chain on E2, forming lipoylysine

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16
Q

What is the function of lipoylysine?

A

Oxidizes hydroxyethyl to acyl groups and attaches in to one of the two sulphur atoms on lipoic acid (breaks disulphide bridge in process)

Acts as a “robotic arm” that carries acetyl group between reactions

17
Q

What is the first step of the PDH mechanism?

A

TPP carbanion attacks pyruvate and decarboxylates it, forming the hydroxyethyl-TPP intermediate

18
Q

What is the second step of the PDH mechanism?

A

2a) Lipoylysine from E2 swings toward E1
2b) Hydroxyethyl-TPP group is oxidize to acetyl group and transferred to lipoylysine arm

19
Q

What is the third step of the PDH mechanism?

A

3a) Lipoylysine arms swings into E2
3b) Acetyl group is transfered to CoASH, forming Acetyl-CoA. Lipoylysine become reduced in the process
3c) Acetyl-CoA leaves PDH complex

20
Q

What is the fourth step of the PDH mechanism?

A

4a) Lipoylysine arms swings to E3
4b) Lipoylysine arm gets oxidized (specifically, the lipoic acid) by FAD, reducing it to FADH2

21
Q

What happens in step 5 of the PDH mechanism?

A

NAD+ enters E3 and oxidizes FADH2 back into FAD. NAD+ gets reduced to NADH + H+ and leaves E3

22
Q

How does Acetyl-CoA affect the PDH complex?

A

It will INHIBIT E2 (product inhibition)

23
Q

How does NADH affect the PDH complex?

A

Will inhibit E3 (Product Inhbition)

24
Q

Where does the majority of PDH complex regulation occur, and how?

A

On E1; through phosphorylation

25
How is E1 of PDH phosphorylated? How is it dephosphorylated?
Phosporylation by PDH Kinase (since it adds phosphoryl groups) Dephosphorylation by PDH phosphatase
26
What molecules allosterically inhibit/activate PDH Kinase?
NAD+ (inhibits), ADP (inhibits) Acetyl CoA (activate), ATP (activates), NADH (activates) Recall that PDH kinase activation will STOP/SLOW DOWN PDH activity, so PDH kinase will be activated when there is HIGH amounts of energy
27
What molecules allosterically inhibit/activate PDH phosphatase?
Insulin (activates), Ca2+ (activates) Recall that PDH phosphatase activation will PROMOTE PDH activity, so PDH phosphatase will be activated when there is LOW amounts of energy Note that Ca2+ is released during muscle contraction, indicating usage of energy (and that more energy is req'd)