In order to regulate the citrate cycle, its various enzymes can be inhibited by different substrates. Sort the substrates into the correct bins depending on whether they inhibit the action of citrate synthase (CS), isocitrate dehydrogenase (ID), or both (CS and ID) Substrates (4 items) (Drag and drop into the appropriate area below) Succinyl-CoA Citrate NADH ATP Enzymes CS ID CS and ID

The citric acid cycle also called the tricarboxylic acid cycle (TCA) or Kreb’s cycle is a catabolic pathway for aerobic organisms. In the cycle, acetyl-coA is metabolized in a series of steps.

The regulation of the cycle is done by the availability of substrates produced within the cycle. It is known as feedback inhibition.

Succinyl-CoA – High concentration of succinyl-CoA inhibits a-ketoglutarate dehydrogenase.

Citrate – CS. Citrate synthase catalyses the combination of acety-CoA with oxaloacetic acid to form citrate. High concentration of citrate inhibits it.

NADH – For isocitrate to be converted to oxalosuccinate, it needs to bind with NAD+. ID catalyses the reaction. NADH inhibits ID by displacing NAD+

ATP Enzymes – CS. ATP inhibits citrate synthase through allosteric inhibition. As more ATP is produces, citrate synthase becomes less saturated with acetyl-CoA, therefore there is less acetyl-Co A to form citrate.