Which process connects glycolysis to the citric acid cycle in mitochondria?

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Glycolysis ends with pyruvate, which must be converted into the substrate that starts the citric acid cycle. In the presence of oxygen, pyruvate enters the mitochondrial matrix and is oxidized by the pyruvate dehydrogenase complex to acetyl-CoA, releasing CO2 and reducing NAD+ to NADH. This acetyl-CoA then combines with oxaloacetate to form citrate, kicking off the citric acid cycle. This step is the essential bridge because it transforms the glycolysis product into the exact substrate that the TCA cycle needs, while also supplying NADH for the electron transport chain. Other options don’t provide this direct link: fermentation happens without entering the mitochondria and doesn’t form acetyl-CoA; photosynthesis is a different energy-harvesting process in plants and some microbes; beta-oxidation breaks down fatty acids into acetyl-CoA but isn’t the direct connection from glycolysis to the TCA cycle.