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Biochem 2 (CHEM 441B) > Ch. 10 > Flashcards

Ch. 10 Flashcards

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1
Q

What does the citrate cycle accomplish for the cell?

A
  • Generate NADH and FADH2 for the ETS
  • Supplies metabolic intermediates for gluconeogenesis, amino acid synthesis, and porphoryn synthesis
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2
Q

What is the net reaction of the citrate cycle?

A

Acetyl-CoA + 3 NAD+ + FAD + GDP + Pi + 2 H2O –> CoA + 2 CO2 + 3 NADH + 3 H+ + FADH2 + GTP

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3
Q

What are the key enzymes in the citrate cycle?

A
  • Pyruvate dehydrogenase: converts pyruvate to acetyl-CoA and CO2
  • Citrate synthase: converts oxaloacetate to citrate and regenerate CoA
  • Isocitrate dehydrogenase: converts isocitrate to α-ketoglutarate, NADH, and CO2
  • α-Ketoglutarate dehydrogenase: α-ketoglutarate to succinyl-CoA
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4
Q

What does 1 round of the citrate cycle yield?

A
  • Transfer of 8 electrons
  • Generates 3 NADH x 2.5 = 7.5 ATP
  • Generates 1 FADH2 x 1.5 = 1.5 ATP
  • 1 GTP = 1 ATP
  • Each cycle results in production of 10 ATP
  • Mostly via oxidative phosphorylation of 3 NADH and 1 FADH2
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5
Q

What 5 coenzymes are required for the pyruvate dehydrogenase complex?

A
  • NAD+
  • FAD
  • CoA
  • Thiamine pyrophosphate (TPP)
  • Alpha-lipoic acid
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6
Q

What is NAD+ derived from?

A

Niacin (vitamin B3)

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7
Q

What is FAD derived from?

A

Riboflavin (vitamin B5)

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8
Q

What is CoA derived from?

A

Vitamin B5
- Generated by Pantothenic acid

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9
Q

What is thiamine pyrophosphate (TPP) derived from?

A

Vitamin B1
- Required for pyruvate dehydrogenase

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10
Q

What does α-lipoic acid do?

A
  • Provides reactive disulfide that participates in redox reactions
  • Accepts and transfers acetyl group to CoA
  • Not a vitamin
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11
Q

What are the 5 steps in the pyruvate dehydrogenase complex?

A

1.Pyruvate binds and is decarboxylated causing the formation of hydroxyethyl-TPP
2. Acetyl group transferred to lipoamide
3. Acetyl group transfered to CoA
4. Dihydroxylipoamide oxidized to lipoamide
5. FAD oxidized forming FADH2 which can reduce NAD+ to NADH

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12
Q

What are negative and positive regulators of PDH?

A

Positive:
- NAD+
- CoA
- ADP

Negative:
- NADH
- Acetyl- CoA
- ADP

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13
Q

What is step 1 of the citrate cycle?

A

Reaction: Condensation
Enzyme: Citrate synthase
Reactants: Oxaloacetate, Acetyl-CoA, and H2O
Product: Citrate

(Highly Favorable)

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14
Q

What is step 2 of the citrate cycle?

A

Reaction: dehydration-hydration
Enzyme: Aconitase
Reactants: Citrate and H2O
Product: (intermediate cis-aconitate) Isocitrate

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15
Q

What is step 3 of the citrate cycle?

A

Reaction: Oxidative decarboxylation
Enzyme: Isocitrate dehydrogenase
Reactants: Isocitrate, NADP+, and H+
Product: NADPH, (intermediate oxalosuccinate), CO2, and alpha ketoglutarate

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16
Q

Which step is the rate limiting reaction in the Citrate cycle?

A

Step 3 or isocitrate dehydrogenase

17
Q

What are positive and negative effectors of Step 3 in the Citrate cycle?

A

Positive:
- ADP and Ca2+

Negative:
- ATP and NADH

18
Q

What is step 4 of the citrate cycle?

A

Reaction: Decarboxylation
Enzyme: α-Ketoglutarate Dehydrogenase (E1, E2, E3)
Reactants: α-Ketoglutarate, CoA, and NAD+
Product: CO2, NADH +H+, and Succinyl-CoA

(Same reaction as Pyruvate dehydrogenase)
(Energetically favorable)

19
Q

What is step 5 in the citrate cycle?

A

Reaction: Substrate level phosphorylation
Enzyme: Succinyl-CoA synthetase
Reactants: Succinyl-CoA, Pi, and GDP
Product: CoA, GTP, and Succinate

20
Q

What is step 6 in the Citrate cycle?

A

Reaction: Oxidation
Enzyme: Succinate dehydrogenase
Reactants: Succinate and FAD
Product: FADH2 and Fumarate

(part of ETC)

21
Q

What is step 7 in the citrate cycle?

A

Reaction: Hydration
Enzyme: Fumarase
Reactants: Fumarate, OH-, and H+
Product: (carbanion intermediate) and Malate

(stereospecific L-isomer)

22
Q

What is step 8 in the Citrate Cycle?

A

Reaction: Oxidation
Enzyme: Malate dehydrogenase
Reactants: Malate and NAD+
Product: NADH + H+ and Oxaloacetate

Biochem 2 (CHEM 441B) (23 decks)

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