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What Do You Actually Need to Know for Biochemical Pathways on the MCAT?

Every MCAT student’s greatest fear: the web of arrows and perplexing jargon to decipher when studying for the biochemistry section. Most students are instantaneously overwhelmed and unsure how to proceed. Your first priority should NOT be memorizing every single reactant, product, and enzyme for each metabolic pathway. While many students are determined to push themselves through this time-intensive brute memorization, the key to the biochemistry section is ultimately prioritizing high-yield content over minute details. The MCAT Biochemistry section ultimately requires a strategic approach to plan your preparation. The primary biochemical pathways that you need to be familiar with for the MCAT are glycolysis, fermentation, Krebs Cycle, electron transport chain/oxidative phosphorylation, gluconeogenesis, glycogenolysis, glycogenesis, fatty acid synthesis, beta-oxidation of fatty acids, and pentose phosphate pathway. So what do you really have to know??

1. Before delving into the details, focus on the overall picture.

It is crucial to know where the metabolic pathways take place at the cellular level and in the body. Furthermore, consider the specific biochemical pathways in relation to the other biochemical pathways. Do two pathways work together, compete with each other, follow sequentially, or serve completely different functions? 

2. Although it seems like common sense, many students blindly memorize minutiae without even understanding the fundamental purpose of the chemical reaction.

Your first goal should be to thoroughly understand the purpose of the biochemical pathway and its final end product. Is it a catabolic or anabolic pathway—does it break down molecules or synthesize new ones? Furthermore, consider how endocrine hormones (such as insulin and glucagon) can affect this pathway.  

3. Rate-limiting steps are key!

Even if you haven’t memorized every step of the pathway, you can still get most of the pathway questions correct! The trick here is to memorize the enzyme, reactant, and product for each rate-limiting step of each biochemical reaction, as these are the highest yield. In order to do this, you first must understand what exactly a rate-limiting step is and what this means for the overall reaction. By thoroughly understanding each rate-limiting step, you can better gauge the reversibility or irreversibility of the pathways and what happens to the pathway if a certain step is affected. 

4. Rate-limiting steps are actually the most regulated steps in biochemical pathways.

It is crucial that you understand the impact on the amount of reactants and products when inhibitors or activators of the reaction are introduced. Being able to critically solve negative and positive feedback questions is vital; for example, if more of a product is introduced, based on Le Chatelier’s principle, the reaction will shift to the reactants. Furthermore, you will also have to know some specific examples of inhibitors and activators for the rate-limiting steps. However, as long as you remember that adding reactants shifts the reaction forward and adding products shifts the rate backward, you should be able to solve most regulation questions. 

5. Now that you’ve covered the highest yield content for the biochemical pathways, it’s time to take this to the next level!

Although it is low-yield, the MCAT can ask questions regarding other steps of biochemical pathways, such as enzymes, reactants, and products. However, memorizing details for some of these pathways is more important than others. For example, you do not necessarily need to know the intricacies of every step of the pentose phosphate pathway, fatty acid synthesis, beta-oxidation, glycogenesis, and glycogenolysis besides the main rate-limiting steps. However, understanding the steps of glycolysis, gluconeogenesis, Krebs cycle, and electron transport chain can be highly beneficial because it allows for a deeper comprehension of organic chemistry passages and experiments. Furthermore, understanding the steps and enzymes that differ in glycolysis and gluconeogenesis is fundamental. 

6. So how do I memorize each of these steps?

Repetition is key! For pathways with countless enzymes and compounds that often sound very similar, staring at these pathways will likely just be a waste of time and effort. Flashcards, such as those by Anki and Blueprint, are great tools to quiz yourself whenever you’re free to ensure that you don’t forget the countless details of the biochemical pathways. Additionally, writing out biochemical pathways repeatedly is highly effective in ensuring that the pathways are committed to memory. 

7. Make the pathways work for you!

Biochemical pathways are overwhelming for most students at first glance, especially when students lack exposure to such terms. Acronyms, either those online, in your content review books, or ones you create, are some of the most useful tricks for ensuring that the biochemical pathways are relatable and memorable. Additionally, although these complex enzyme functions and substrate terms often seem like a foreign language, breaking down the root words, prefixes, and suffixes of these components can be extremely helpful. Consider what an enzyme is really doing: is it rearranging the substrate, phosphorylating the substrate at certain positions, or facilitating a redox chemical reaction? (In that case, this is an isomerase, kinase, and dehydrogenase, respectively.) Furthermore, keeping track of the number of carbons, especially in glucose metabolism, and the number of phosphates can help ease the memorization of enzyme and substrate names. While it may seem counterintuitive, developing a deeper understanding of these cellular processes actually reduces the stress and effort you have to invest in memorization. 

Biochemical pathways can often seem like another language in their complex terminology. However, like any language, the most difficult, fundamental phase is getting started. Once you start piecing together the highest-yield concepts through your unique memorization techniques, everything will slowly fall into place. Hopefully you’ll now be able to attack the highest-yield topics to strategize your studying and catalyze your success! For more content review, check out our amino acids tips.

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