The first reaction in the citric acid cycle is binding A) carbon dioxide to a four-carbon (C₄) molecule. B) carbon dioxide to a five-carbon (C₅) molecule. C) acetyl-CoA to a C₅ molecule. D) acetyl-CoA to a C₄ molecule.

Question

Quizplus · Accepted Answer

The first reaction in the citric acid cycle is the binding of acetyl-CoA (a two-carbon molecule) to a four-carbon molecule called oxaloacetate, forming a six-carbon molecule called citrate. Therefore, the best choice is D which states that acetyl-CoA binds to a four-carbon molecule (C₄). Choices A and B are incorrect because carbon dioxide is not involved in the first reaction of the citric acid cycle. Choice C is also incorrect because acetyl-CoA does not bind to a five-carbon molecule in the first reaction.

The First Reaction in the Citric Acid Cycle Is Binding