The Citric Acid Cycle
Lesson Learning Outcomes
Upon the completion of this chapter, students should be able to: Explain the steps of the citric acid cycle. Differentiate between citric acid cycle and glyoxylate cycle. Relate citric acid cycle as energy source.
The Central Role of the Citric Acid Cycle
3 processes play central roles in aerobic metabolism.
The citric acid cycle. Electron transport . Oxidative phosphorylation.
Metabolism consists of:
Catabolism: the oxidative breakdown of nutrients. Anabolism: the reductive synthesis of biomolecules.
•
The citric acid cycle is amphibolic that is, it plays a role in both catabolism and anabolism. It is the central metabolic pathway.
Relationship of TCA Cycle to Catabolism
Amino acids, fatty acids and glucose can all produce acetyl-CoA in stage 1 of catabolism. In stage 2, acetyl-CoA enters the citric acid cycle. Stage 1 and 2 produce reduced electron carriers. In stage 3, the electrons enter the electron transport chain, which then produces ATP.
Where does the Citric Acid Cycle Take Place?
In eukaryotes, the cycle takes place in the mitochondrial matrix.
Features of Citric Acid Cycle
• Pyruvate produced by glycolysis is transformed by oxidative decarboxylation into acetyl-CoA in the presence of coenzyme A.
• Acetyl-CoA enters citric acid cycle by react with oxaloacetate to produce citrate.
• The reactions of the citric acid cycle include two other oxidative decarboxylation, which transform citrate into succinate. • The cycle is complete by regenaration of oxaloacetate from succinate in a multistep process that includes two other oxidation reactions. Pyruvate + 4NAD+ + FAD + GDP + Pi + 2H2O 3CO2 + 4NADH + FADH2 + GTP + 4H+
• The cycle is strongly exergonic.
Pyruvate is Converted to Acetyl-CoA
Pyruvate dehydrogenase complex is responsible for the conversion of pyruvate to CO2 and the acetyl portion of acetyl-CoA. Five enzymes in complex:
1. 2. 3. 4. 5.
Upon the completion of this chapter, students should be able to: Explain the steps of the citric acid cycle. Differentiate between citric acid cycle and glyoxylate cycle. Relate citric acid cycle as energy source.
The Central Role of the Citric Acid Cycle
3 processes play central roles in aerobic metabolism.
The citric acid cycle. Electron transport . Oxidative phosphorylation.
Metabolism consists of:
Catabolism: the oxidative breakdown of nutrients. Anabolism: the reductive synthesis of biomolecules.
•
The citric acid cycle is amphibolic that is, it plays a role in both catabolism and anabolism. It is the central metabolic pathway.
Relationship of TCA Cycle to Catabolism
Amino acids, fatty acids and glucose can all produce acetyl-CoA in stage 1 of catabolism. In stage 2, acetyl-CoA enters the citric acid cycle. Stage 1 and 2 produce reduced electron carriers. In stage 3, the electrons enter the electron transport chain, which then produces ATP.
Where does the Citric Acid Cycle Take Place?
In eukaryotes, the cycle takes place in the mitochondrial matrix.
Features of Citric Acid Cycle
• Pyruvate produced by glycolysis is transformed by oxidative decarboxylation into acetyl-CoA in the presence of coenzyme A.
• Acetyl-CoA enters citric acid cycle by react with oxaloacetate to produce citrate.
• The reactions of the citric acid cycle include two other oxidative decarboxylation, which transform citrate into succinate. • The cycle is complete by regenaration of oxaloacetate from succinate in a multistep process that includes two other oxidation reactions. Pyruvate + 4NAD+ + FAD + GDP + Pi + 2H2O 3CO2 + 4NADH + FADH2 + GTP + 4H+
• The cycle is strongly exergonic.
Pyruvate is Converted to Acetyl-CoA
Pyruvate dehydrogenase complex is responsible for the conversion of pyruvate to CO2 and the acetyl portion of acetyl-CoA. Five enzymes in complex:
1. 2. 3. 4. 5.