Recall that the citric acid cycle starts with a four-carbon molecule, but that most of its intermediates are molecules that contain six carbons. How is this possible?

Question

Quizplus · Accepted Answer

The citric acid cycle starts with the four-carbon molecule oxaloacetate combining with acetyl-CoA to form the six-carbon molecule citrate. Through a series of reactions, citrate is converted to isocitrate (six carbons), α-ketoglutarate (five carbons), succinyl-CoA (four carbons), succinate (four carbons), fumarate (four carbons), and finally malate (four carbons). The cycle is then completed when malate is converted back to oxaloacetate (four carbons), thus starting the process over again. Therefore, it is through the reaction of acetyl-CoA and oxaloacetate that the citric acid cycle intermediates gain two additional carbons.

Recall That the Citric Acid Cycle Starts with a Four-Carbon