We will use the Interdisciplinary Discussions to provide a bit of commentary on the citric acid cycle as we did with glycolysis. Please bear in mind that biochemistry is not an MCAT prerequesite. However, the expectation on the exam is a bit more advanced in the biochemistry topics than the typical Bio 101 course. Furthermore, biochemistry exerts a pull on the organic chemistry emphasis. Reactions which are very important in biochemistry appear on the MCAT with great frequency. So rest assured that the exam will not be interested in very specific recall regarding biochemical pathways. However, preparing your ability to read and comprehend passages with biochemistry nomenclature is an important task for the MCAT. In summary, although you are not expected to have mastered Biochemistry before the MCAT, a good comfort level with the subject matter is essential for a superior score.

It is a good idea to open your biology textbook to its graphic of the citric acid cycle pathway as you read these discussions. Let us begin our discussion of the citric acid cycle with acetyl CoA, our two carbon remainder from glycolysis. In a series of reactions catalyzed by citrate synthase, acetyl CoA first combines with oxaloacetate, a four carbon form, by means of an aldol condensation (aldol condensation again!). The CoA portion of is then removed by hydrolysis of the thioester linkage in an acyl exchange mechanism.