Which process connects glycolysis and the citric acid cycle

acetyl CoA formation.

The correct answer is Link reaction ( formation of acetyle CoA from pyruvate).

In this reaction acetyl-Coenzyme A ( which is a two-carbon molecule) is produced from pyruvate ( three-carbon molecule, produced from glycolysis). Acetyl CoA is required for the citric acid cycle.  

In the link reaction, two molecules of hydrogen and CO₂ are released from two molecules of pyruvate, forming two acetyl CoA.

This reaction occurs in the mitochondrial matrix

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