Chapter 18- Citric Acid Cycle Prep (PDH)

Question 1

What is the pyruvate dehydrogenase complex reaction?
Three enzymes used?
5 cofactors (coenzymes/prosthetic groups)?

Answer 1

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Pyruvate is converted to acetyl CoA (energy source for citric acid cycle)
Enzymes:
Pyruvate dehydrogenase (E1), dihyrdolipoyl transacetylase (E2), highdrolipoyl dehydrogenase (E3)
Cofactors:
Thiamine pyrophosphate (TPP) (prosthetic group)
Lipoic Acid (prosthetic group)
Coenzyme A
Flavin adenine dinucleotode (FAD) (prosthetic group)
Nicotinamide adenine dinucleotide (NAD+)

Question 2

What is the structure (components) of Coenzyme A?

Slide 5

Answer 2

β-mercaptoethylanine
Panthothenic acid
3’-phosphoadenosine diphosphate

Question 3

What is the prosthetic group of each of the 3 enzymes:
Pyruvate dehydrogenase component (PDH)
Dihydrolipoyl transacetylase (DHT)
Dihydrolipoyl dehydrogenase (DHDH)

Answer 3

PDH- TPP (thiamine pyrophosphate)
DHT- lipoamide
DHDH- FAD (flavin adenine dinucleotide)

Question 4

What are the 6 reactions in converting pyruvate to acetyl CoA?
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Answer 4

Remember the three enzymes and their prosthetic groups

Question 5

What is the overall simple reaction from glucose to acetyl CoA?

Answer 5

Glucose -> 2 pyruvate -> 2 Acetyl CoA + 2 NADH + 2CO2

Question 6

What are the jobs of the 3 enzymes of PDH?

Answer 6

E1 (Pyruvate Dehydrogenase component)- decarboxylation of pyruvate and transfer 2 carbon unit to E2
E2 (dihydrolipoyl transacetylase)- transfer of acetyl moiety to CoA to synthesize acetyl CoA
E3 (dihydrolipoyl dehydrogenase)- regenerates oxidized lipoyl group of E2 and transfers protons and electrons first to FAD and then to NAD complete the reaction cycle

Question 7

What is high energy charge and low energy charge
Slides 9-10
What inhibit and activate PDH?

Answer 7

High energy- don’t need reaction of PDH, so you inhibit it
NADH, ATP, And Acetyl CoA can inhibit
Low energy- need reaction, so activate it
Pyruvate and ADP activate

Question 8

How does PDH cycle between inactive and active form?

Which form is phosphorylated?

Answer 8

Enzyme kinase inactivates PDH
Enzyme phosphatase activates PDH
Active PDH- dephosphorylated
Inactive PDH- phosphorylated

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