Consider the following steps of the Tricarboxylic Acid (TCA) cycle: I. Conversion of isocitrate to -ketoglutaric acid II. Conversion of succinyl-CoA to succinic acid III. Conversion of -ketoglutaric acid to succinyl-CoA IV. Conversion of succinic acid to malic acid In which of the above steps does decarboxylation take place?

Step-by-step solution

The Tricarboxylic Acid (TCA) cycle involves two decarboxylation steps where a carbon atom is removed in the form of CO₂ . In step I, isocitrate (a 6-carbon compound) undergoes oxidative decarboxylation to form -ketoglutaric acid (a 5-carbon compound), releasing one molecule of CO₂ . In step III, -ketoglutaric acid (5-carbon) undergoes another oxidative decarboxylation to form succinyl-CoA (a 4-carbon compound), releasing another molecule of CO₂ . Step II involves the conversion of succinyl-CoA to succinic acid, whi