Reviewed by:
Third-Year Medical Student, Lewis Katz School of Medicine at Temple University
Reviewed: 12/11/23
Studying for MCAT biochemistry and not sure where to start? This study guide will go over some essential biochemistry focus topics, sample questions, and answer a few FAQs to get you on the right track.
If you’re looking to pursue an education as a medical student, you’ll likely have a general understanding of what the Medical College Admissions Test (MCAT) entails. In addition to bringing your ID and water bottle on MCAT day, you’re going to need to bring to the MCAT lots of strong knowledge!
This article will go over the basics of the Biochemistry MCAT. We will discuss how the MCAT covers biochemistry, sample MCAT biochemistry questions and answers, and some frequently asked questions.
The MCAT is a computer-based multiple-choice test. Its purpose is to assess your foundational understanding of scientific and behavioral concepts that determine your likelihood of success in medical school. You will be given 95 minutes to complete the 59 questions within each section, made up of passage-based and discrete questions.
25% of questions in MCAT’s Biological and Biochemical Foundations of Living Systems section cover concepts in biochemistry. The biochemistry section is designed to assess your conceptual understanding of first-semester biochemistry topics taught at the college level.
This section will test your understanding of foundational concepts, scientific inquiry, and reasoning skills. You will be tested on cycles and biochemical pathways on the MCAT.
You can expect these approximate percentages in the MCAT Biological and Biochemical Foundations of Living Systems section:
Source: The Association of American Medical Colleges (AAMC)
With this in mind, we will cover the main biochemistry topics you’ll find on the MCAT in the following section.
The MCAT biochemistry questions will cover the following topics:
Since your first-semester biochemistry class was likely ages ago, you might find remembering everything a bit challenging. In this study guide, we will briefly break down each concept and discuss some terms to focus on as you study for your biochemistry MCAT.
An understanding of amino acids, peptides, and proteins is foundational in the biochemistry of living systems. This section will break down what you need to know about them for your MCAT.
Amino acids are building blocks for proteins. The biochemistry MCAT will focus primarily on alpha-amino acids and the molecules that make them up. The MCAT will expect you to memorize the 20 alpha-amino acids, their structures, full name, three-letter code, and single-letter code.
It is also necessary for you to have a thorough understanding of the properties of amino acids. For instance, you’ll want to know how an amino acid’s charge might change depending on its environment’s pH level and how amino acids are synthesized.
Finally, the MCAT will require you to understand the classifications of amino acids. Specifically, their acidic or basic classifications and their hydrophobic and hydrophilic classifications.
A peptide is a string of 2-50 bonded amino acids. For the biochemistry MCAT, there are three primary reactions that you must remember:
Understanding how these reactions occur will ultimately allow you to determine a polypeptide’s structure and function, which is essential for this section of the MCAT.
In addition to the components and processes that make up proteins, the biochemistry MCAT will require you to understand the general principles and structures of proteins. It is integral that you become familiar with the following concepts:
It will also be essential to know the processes that lead to the formation of these structures. For instance, it will serve to know that Primary structures link through covalent bonds and that secondary structures are a result of inter- or intramolecular hydrogen bonding.
Now that we have gone over proteins, we will be going over protein function. Enzymes are proteins that act as catalysts, increasing the rate at which a chemical reaction occurs. For the MCAT, it is important to know how an enzyme functions and the process by which it is able to accelerate a chemical reaction.
The biochemistry MCAT will also test you on the classification of enzymes by reaction type, how these reactions take place, or the mechanism of catalysis. You should also know what types of ions and molecules assist enzymes throughout these processes.
Finally, you will want to understand how certain environmental conditions affect enzyme activity and reactions. Recall that enzymes are proteins in action and are built from amino acid chains (peptides). The charge of amino acids can change depending on the environment; therefore, differences in temperature or pH can impact enzymatic activity.
Aside from their enzymatic function, proteins also have non-enzymatic functions. Proteins can serve structure, transportation, regulation, movement, and immune defense.
For the biochemistry portion of the MCAT, it is important to know the three primary non-enzymatic functions of proteins: binding, immune system, and motors. Here are the basics of what you need to know:
In this section, we will be going over what you need to know about DNA and RNA for the biochemistry MCAT. We will be looking at their respective structures, components, differences, and functions.
Nucleotides are the most basic components of RNA and DNA. Nucleotides consist of a sugar, a phosphate group, and a nitrogenous base. Nucleosides, on the other hand, are slightly different in that they do not have a nitrogenous base.
DNA, or Deoxyribonucleic Acid, is a double-helix structure that stores genetic information of living things. For the biochemistry MCAT, you must understand DNA structure and its components. As mentioned, the sugar-phosphate backbone is made up of nucleotides. Nitrogenous bases you can find in DNA are adenine, cytosine, guanine, and thymine.
These bases are paired with hydrogen bonds to form the DNA’s double-helix structure. Adenine pairs with thymine, and guanine pairs with cytosine.
RNA (ribonucleic acid) is a single-stranded structure with a ribose and phosphate backbone. Like DNA, RNA contains nitrogenous bases adenine, cytosine, and guanine. Uracil takes the place of thymine in base pairing for RNA.
For the biochemistry MCAT, you must be able to differentiate RNA from DNA in location, function, structure, reproduction, and base pairing.
Source: Research Gate
The classifications of nucleotides found in both DNA and RNA are purines and pyrimidines. You should know that the difference between the two is based on their structure; purines have a double-ring structure, and pyrimidines have a single-ring structure. These classifications are as follows:
In terms of DNA and RNA on the biochemistry MCAT, you will have to acquire a good understanding of these structures and how they are formed, their classifications, their functions, and how they replicate.
Carbohydrates work to produce energy for cells. They consist of carbon-containing sugar molecules that integrate hydrogen and oxygen. Structurally, carbohydrates are simply a chain of carbon atoms. For the biochemistry MCAT, you must know carbohydrate nomenclature, classification, and common names.
Another vital thing to understand is the absolute configuration of carbohydrates. You will have to know how atoms in carbohydrates are arranged based on the highest-numbered chiral carbon.
In addition to absolute configuration, the biochemistry MCAT will also test you on the cyclic structure and conformations of hexoses. Hexoses can switch from a chain to cyclic formations. Understand how these structures form and how they can affect intermolecular reactions.
Finally, know what epimers and anomers are and how they contribute to a carbohydrate’s structure.
For your biochemistry MCAT, you will have to know how carbohydrates bond with each other through glycosidic linkage. Understand the process in which these bonds occur and the type of carbohydrates they produce.
Specifically, you will want to know the following categories of carbohydrates and their types, their structures, and their functions:
Lipids are hydrophobic molecules composed of three long hydrocarbon tails attached to a glycerol molecule. There are different types of lipids:
For the biochemistry MCAT, know the molecular structure of each of these lipids, their distinctions, and their functions within living systems. Also, know the different types of fatty acid chains that can make up certain lipids. Examples include saturated or unsaturated fats, trans fats, and omega fatty acids.
Gluconeogenesis is a process that enables glucose production from noncarbohydrates such as fats and proteins. For this section of the biochemistry MCAT, you will have to know how, where, and why gluconeogenesis occurs.
Finally, you will want to know what precursors are necessary for the occurrence of gluconeogenesis, such as lactate, glycerol, and amino acids, among others. It is integral to understand the gluconeogenesis pathway and its parts for your biochemistry MCAT.
This section will cover what you need to know about protein and lipid metabolism for your biochemistry MCAT. We will briefly cover some basic terms and constituents of each process.
As we’ve covered, proteins are essential to the function of living systems. Our bodies are not able to synthesize certain amino acids; therefore, some of these proteins must come from one’s diet, supplements, and other sources.
As we digest these proteins, they are broken down into new amino acids, absorbed into the bloodstream, and then into the liver to synthesize new proteins.
For the biochemistry MCAT, you must know the three digestive enzymes that break down proteins: trypsin, chymotrypsin, and carboxypeptidase. You will also have to know how they are degraded through deamination, how they are absorbed, and how they circulate throughout the body.
Lipid Metabolism is the process by which fats are broken down and synthesized. Fats are triglycerides found in one’s diet, adipose tissue, or synthesized from excess carbohydrates. These fats are first broken down via the digestive system.
For the biochemistry MCAT, you will have to know the elements that aid the synthesis of fats during digestion (i.e., bile salts and pancreatic lipase).
After the initial digestion of lipids, they break down into monoglycerides, free fatty acids, and glycerol. They then move through the intestinal epithelium and eventually reconstruct into triglycerides. Know that fats are hydrophobic in nature and require lipoproteins to move through aqueous environments.
The biochemistry MCAT will require you to understand the biochemical processes in which these fats are processed, mobilized, and stored throughout the body.
Now that we have gone over the basics of what you need to know for MCAT biochemistry, we will be going over some sample questions, answers, and explanations. These samples will allow you to understand how you can apply your knowledge. You’ll also better understand how MCAT questions are formulated and reasoned.
“Question 1. A new test involving precipitation has been developed to find proteins in urine. However, complications have arisen due precipitation of calcium phosphate. Which of the following procedures could prevent the precipitation of the salt?
A) Adding a buffer in order to maintain a high pH
B) Adding a buffer so a neutral pH can be maintained
C) Adding calcium hydroxide to the test
D) Adding sodium phosphate to the test
Answer:
The correct answer is B: Here, the question asks the examinee to point out a change in an experimental/scientific approach that has the ability to eliminate a repeated complication. To respond to this question correctly, the examinee must reason about how varying the experimental parameters of the test would eliminate the current complication.”
In addition to stand-alone multiple-choice questions, the MCAT will also have passage-based questions similar to the following:
“The myocellular transmembrane Na+ gradient is important for proper cellular function. During septic shock, disruption of Na+ homeostasis often occurs and leads to decreased membrane potential and increased intracellular Na+.
It has been found that failure of cellular energy metabolism is a common symptom in septic patients who do not respond to therapeutics. Because normal intracellular levels of Na+ are maintained by the Na+K+ ATPase, it is important to understand how metabolic energy production is linked to cation transport.
Researchers are interested in whether the energy used for ion transport is derived from glycolysis or oxidative phosphorylation. This information would provide a better understanding of myocellular damage that occurs during critical illness. Experiments were conducted to evaluate the effects of glycolytic inhibition on cellular Na+ and K+ concentrations and lactate production in rat skeletal myocytes.
Rat skeletal muscle fibers were extracted and incubated in normal media (control), glucose-free media (G(–)), and glucose-free media with various concentrations of the glycolytic inhibitor iodoacetate (IAA). IAA directly prevents the formation of 1,3-bisphosphoglycerate.
After one hour in the media, the muscle tissues were assayed for intracellular Na+ and K+ content and lactate production. Cellular viability was determined by measuring the amount of lactate dehydrogenase (LDH) released, as LDH release is an indicator of cell death. The results are displayed in Figure 1.
Figure 1 Effects of glycolytic inhibition on intracellular Na+ and K+ content and lactate production with cellular viability measured by LDH release. (Note: The * indicates p < 0.05 versus control.)
The researchers also examined the effect disruption of oxidative phosphorylation had on Na+ and K+ content. Inhibition of oxidative phosphorylation was caused by carbonyl-cyanide m-chlorophenylhydrazone (CCCP), an ionophore that allows protons to move freely through membranes. No correlation between Na+ and K+ content and oxidative phosphorylation was found.
Question 1. The researchers chose a concentration of 0.3 mM IAA as the working concentration for any additional studies instead of 1 mM or 2 mM. What is the likely reason for this?
A) The lower concentration of IAA gave the largest Na+ response.
B) Higher concentrations induced significant cytotoxicity.
C) The solubility of IAA was not high enough.
D) The researchers were trying to mimic control conditions as closely as possible.
Answer:
Correct Answer is B) Higher concentrations induced significant cytotoxicity.
Rationale: Here, the examinee must have an understanding of cell lysis and cytotoxicity in an experimental design, as the passage outlines. More specifically, when it comes to conducting an experiment where the level of IAA was cytotoxic to the cells, test takers must know that these cells would lose membrane integrity and suffer lysis. Therefore, they are not ideal for comprehending the role glycolysis plays in establishing ion concentration gradients. Considering all factors, the experimental design should avoid using a concentration of IAA concentration that greatly increases cell lysis.
Question 2. The information in the passage suggests that glycolysis:
A) is important for maintaining normal Na+ and K+ levels in skeletal muscle.
B) facilitates membrane permeability in skeletal muscle.
C) impedes the function of the Na+ and K+ ATPase in skeletal muscle.
D) is regulated by the Na+ and K+ ATPase in skeletal muscle.
Answer:
Correct Answer is A) is important for maintaining normal Na+ and K+ levels in skeletal muscle.
Rationale: Here, the examinee must use their knowledge of glycolysis to properly analyze the experimental data shown in Figure 1. More specifically, the examinee needs to spot the data trend that demonstrates a correlation between the role of IAA in the distribution of glycolysis; a rising IAA concentration leads to a higher NA+ to K+ concentration than was observed in the control sample.
The above conclusion is also supported by the data in Figure 1, which shows a drop in lactate production at higher IAA concentrations. IAA inhibits NADH formation, which is used when lactate is produced from pyruvate.
IAA’s proposed role, combined with Figure 1’s results, causes examinees to conclude that glycolysis is important to the Na+K+ ATPase. It is also, therefore, significant to maintaining the concentration ratio of Na+ to the K+.
Question 3. If the effects of IAA treatment in nerve cells are the same as those observed in myocytes, which feature of an action potential would be most affected by IAA treatment?
A) Initiation of depolarization
B) Rising phase of depolarization
C) Falling phase to undershoot
D) Return to resting potential
Answer:
Correct Answer is D) Return to resting potential.
Rationale: Here, the examinee must recall the role Na+K+ ATPase plays in the recovery of the nerve cell’s resting potential. Additionally, the examinee must use information from the passage to explain the effect of IAA treatment as well as how the IAA’s hindrance of glycolysis impacts ATP’s cellular concentration. Considering the two factors above, the examinee can come up with a hypothesis on how much of an action potential would be changed by IAA treatment.”
Familiarizing yourself with practice questions like this is an essential part of studying for the MCAT.
Now that we’ve covered topics and some sample questions for the biochemistry section on the MCAT, we will be answering some FAQs to address any questions you might still have.
Biochemistry is a part of the Biological and Biochemical Foundations of Living Systems section on the MCAT. You will also find some biochemistry in the Chemical and Physical Foundations of Living Systems.
Biochemistry consists of approximately 25% of the MCAT.
Although you can always teach yourself biochemistry for the MCAT, the content is dense and will require a pre-existing understanding of the subject matter. Self-teaching may also put you at a disadvantage in terms of time and efficiency when studying for your MCAT.
Biochemistry is a necessary prerequisite to taking the MCAT. You will be explicitly tested on first-semester biochemistry.
It always helps to have a plan and create a study schedule. It is best to choose courses that will help you prepare for the exam and begin studying well in advance.
For the biochemistry portion of the MCAT, it is critical to develop a practical understanding of the general concepts discussed in this article. Now that you have an overview of what you need to know for the biochemistry MCAT, you’ll find it easier to navigate your MCAT biochemistry review and plan out your study schedule.
Remember that the MCAT will require you to understand how each relevant structure interacts with one another and their environment. The biochemistry MCAT will also expect an understanding of how these concepts operate within living systems. With this said, make sure to allot enough time to study each of its components. Best of luck!
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