The most important thing to keep in mind regarding the MCAT is that it's NOT a detail-oriented exam but rather a critical thinking test. Thus, you need not learn all the excruciating details of intermediary metabolism, there are only a few major facts and concepts that you should bring with you to test day; everything else will be provided for you in the MCAT passage:
1. The purpose of each biochemical pathway. For instance, glycolysis partially oxidizes glucose, thereby generating some reducing power (high energy electrons in NADH) and some ATP. THe Krebs cycle fully oxidizes what is left of glucose, following glycolysis and pyruvate decarboxylation, thereby generating a ton of NADH and FADH2 (and a modicum of ATP); further, the Krebs cycle functions as a sort of hub of metabolism, meaning that a lot of things feed into it and many things can be synthesized from the intermediates in the cycle.
2. The location of each process (e.g., pyruvate decarboxylation occurs in the mitochondrial matrix) and the implications of this location from the standpoint of energy production--HINT: the NADH produced by glycolysis must go to the inner mitochondrial membrane to participate in oxidative phosphorylation, but NADH doesn't exactly cross biological membranes with ease.
3. Understand negative and positive feedback--this is REALLY important.
4. Understand the significance of aerobic and anaerobic environments (e.g., when oxygen is not present, then fermentation occurs and the Krebs cycle and ETC are inactive)
5. Know the ultimate products of each pathway, but not necessarily the exact number of each product, the one exception being the number of ATP's generated by each pathway.
6. Know the relationships between electron shuttling, proton movement across biological membranes, and phosphorylation of ADP in the electron transport chain. It's critical that you fully understand why the ETC relies on an electrochemical gradient for ATP generation.