Cellular Respiration Quiz

The Link Between Glycolysis and the Citric Acid Cycle

• Glycolysis occurs in the cytoplasm of the cell while the citric acid cycle takes place in the mitochondria.
• Pyruvate, a product of glycolysis, must be transported into the mitochondria for aerobic metabolism.
• In the mitochondrial matrix, pyruvate is oxidatively decarboxylated by the pyruvate dehydrogenase complex to form acetyl CoA.
• The conversion of pyruvate into acetyl CoA is irreversible and commits carbon atoms to oxidation by the citric acid cycle.
• The pyruvate dehydrogenase complex produces high-transfer-potential electrons in the form of NADH.
• Fatty acid degradation is another source of acetyl CoA for the citric acid cycle.
• The pyruvate dehydrogenase complex is a large, highly integrated complex of three distinct enzymes with its own active site.
• The complex is a member of a family of extremely large similar complexes with molecular masses ranging from 4 million to 10 million daltons.
• The synthesis of acetyl Coenzyme A from pyruvate requires three enzymes and five coenzymes.
• The reaction requires the participation of catalytic coenzymes, such as thiamine pyrophosphate (TPP), lipoic acid, and flavin adenine dinucleotide (FAD), and stoichiometric coenzymes, such as CoA and nicotinamide adenine dinucleotide.
• The conversion of pyruvate into acetyl CoA consists of three steps: decarboxylation, oxidation, and transfer of the resultant acetyl group to CoA.
• The steps must be coupled to preserve the free energy derived from the decarboxylation step to drive the formation of NADH and acetyl CoA.

The Mechanism of Acetyl Coenzyme A Synthesis from Pyruvate

• Glycolysis occurs in the cytoplasm of the cell, while the citric acid cycle occurs in mitochondria.
• Pyruvate is transported into mitochondria to be aerobically metabolized.
• Pyruvate is oxidatively decarboxylated by the pyruvate dehydrogenase complex to form acetyl CoA in the mitochondrial matrix.
• The conversion of pyruvate into acetyl CoA is irreversible and commits the carbon atoms of carbohydrates to oxidation by the citric acid cycle or to the synthesis of fatty acids.
• The pyruvate dehydrogenase complex produces and captures high-transfer-potential electrons in the form of NADH, foreshadowing the key features of the reactions of the citric acid cycle.
• Pyruvate produced by glycolysis is converted into acetyl CoA, the fuel of the citric acid cycle.
• The pyruvate dehydrogenase complex is a large, highly integrated complex of three distinct enzymes, each with its own active site.
• The pyruvate dehydrogenase complex is a member of a family of extremely large similar complexes with molecular masses ranging from 4 million to 10 million daltons.
• The synthesis of acetyl Coenzyme A from pyruvate requires three enzymes and five coenzymes.
• The conversion of pyruvate into acetyl CoA consists of three steps: decarboxylation, oxidation, and the transfer of the resultant acetyl group to CoA.
• The coenzymes thiamine pyrophosphate (TPP), lipoic acid, and flavin adenine dinucleotide (FAD) serve as catalytic coenzymes, and CoA and nicotinamide adenine dinucleotide are stoichiometric coenzymes.
• The mechanism of the pyruvate dehydrogenase reaction is wonderfully complex, requiring the participation of the three enzymes of the pyruvate dehydrogenase complex and five coenzymes.