Fate of Pyruvate

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Fate of Pyruvate Citric Acid Cycle

• Introduction of Glucose Metabolism
• Lecture-3

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Fate of pyruvate

• 1- Lactate (in cytosol)
• Enzyme lactate dehyrogenase (LDH)
• in anaerobic glycolysis
• 2- Acetyl CoA
• in mitochondria
• Enzyme pyruvate dehydrogenase
• occurs in aerobic glycolysis
• Acetyl CoA is required for citric acid
  cycle (CAC)
• 3- Oxalacetate
• in mitochondria
• Enzyme pyruvate carboxylase
• Oxalacetate is required for
• 1- Citric acid cycle (condenses with
  acetyl CoA) to yield energy ATP
• OR 2-Gluconeogenesis (to synthesize glucose)

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Fate of Pyruvate
Glucose
glycolysis
Gluconeogenesis
No Oxygen No Mitochondria OR BOTH
mitochondria
PYRUVATE
LACTATE
OXALACETATE
Oxygen Mitochondria
ACETYL CoA
CITRIC ACID CYCLE
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LACTATE DEHYDROGENASE
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FATES OF PYRUVATE
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OXIDATIVE DECARBOXYLATION OF PYRUVATE
Allosteric Regulation
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Formation of acetyl CoA from pyruvate

• Pyruvate (end product of aerobic glycolysis) is
  transported into the mitochondria.
• In the mitochondrial matrix, pyruvate is
  converted to acetyl CoA by
• pyruvate dehydrogenase complex
  (multienzyme complex)
• This reaction is irreversible
• Pyruvate dehydrogenase complex is composed of
  three enzymes five coenzymes
• Coenzymes of the complex are derived from water
  soluble vitamins
• 1- Thiamine pyruphosphate, TPP (derived
  from thiamine, vitamin B1)
• 2- NAD (derived from niacin)
• 3- FAD (derived from riboflavin)
• 4- Lipoic acid
• 5- Coenzyme A (derived from pantothenic
  acid)

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Pyruvate dehydrogenase complex
PYRUVATE
ACETYL CoA
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Citric acid cycle or,(Krebs cycle)
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Citric Acid Cycle

• Citric acid cycle
• is the final pathway where the oxidative
  metabolism of
• Carbohydrates (as glucose), proteins (amino
  acids) lipids (fatty acids)
• to yield energy (ATP)

Acetyl CoA is the end product for oxidation of
carbohydrates, lipids proteins Acetyl CoA
condenses with oxalacetate to form citrate
(first reaction of the cycle) 3 NADH are
produced 3 X 3 9 ATP (by oxidative
phosphorylation) One FADH2 is produced 1 X 2
2 ATP (by oxidative phosphorylation) One ATP is
produced (by substrate level phosphorylation) Net
12 ATP / one acetyl CoA
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Citric Acid Cycle CYCLE - SUMMARY
Acetyl CoA
3 NAD
3 NADH H
2 CO2
1 FAD
1 FADH2
1 ADP
1 ATP
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KREBS CYCLE REACTIONS (1)
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KREBS CYCLE REACTIONS (2)
Succinate Thiokinase
Substrate-Level Phosphorylation
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KREBS CYCLE REACTIONS (3)
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KREBS CYCLE ENERGY YIELD
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Citric acid cycle or,(Krebs cycle)