Despite conflicting information from test prep companies and vagueness on behalf of the AAMC, you need to know your amino acid structures, chemical properties, 3-letter and 1-letter names. I highly recommend that, before test day, you be able to recreate the structures (by hand) of all of the 20 amino acids. The reason why this is important is because the MCAT will often modify one of the amino acids very slightly and then ask you to identify it. Learning how to draw the amino acids from scratch will not only give you more insight as to how polypeptides are synthesized in the body (the amino group performs a nucleophilic attack on the carboxyl, causing growth from the N to C direction) but will ensure that you can quickly name or draw parallels to known amino acids without hesitation.  
 
In this blog post, I will point out important features of amino acids that you should know and some tips on how to learn them.
 
First off, all of the twenty amino acids you are expected to know are alpha amino acids. This means that there is only one carbon (the alpha carbon) attached to the carboxylic acid group. These amino acids, in general, consist of an amino group (which, under physiological conditions is always protonated, pKa ~ 9), the alpha carbon (which is connected to one hydrogen and the R group) and the carboxylic acid group (always deprotonated under physiological conditions, pKa ~ 2).
 
The Fischer projections of the naturally occurring amino acids in the body tell us that all the chiral amino acids (which includes all of them except glycine, with two hydrogens attached to the alpha carbon) are L amino acids. This means that in the Fischer projection, the amino group is on the left side.
 
18 out of the 19 L amino acids rotate plane polarized light in the counter-clockwise direction, meaning that they are S (remember, the D/L conventions do not necessarily correlate with the R/S conventions). Only cysteine is R due to the higher priority of the sulfur atom over the oxygen. Despite this, cysteine is still an L amino acid because the positioning of all the groups still matches the L form of the Fischer projection (D/L conventions don’t use Cahn-Ingold-Prelog priority assignments).
 
Finally, of course, know all the chemical properties of the amino acids. All amino acids are polar to some extent (since they exist as zwitterions and contain a number of hydrogen bond donors and acceptors) but, rather, are classified based on the identity of their R group. Glycine, Alanine, Valine, Leucine, Isoleucine, Proline, and Methionine are non-polar and non-aromatic (aliphatic). Methionine is sulfur-containing, making it a good candidate to track via radioactive sulfur labeling. The non-polar amino acids tend to be found in the interior of proteins and the increase in entropy as a result of the formation of their hydrophobic interactions and the subsequent release of water drive polypeptide folding. Phenylalanine, Tyrosine, and Tryptophan are aromatic amino acids. They can form stable structures through pi-stacking. Asparagine, Glutamine, Serine, Threonine and Cysteine are polar and tend be found on the exterior of proteins, forming interactions with water, salts, and other polar compounds. Glutamate and Aspartate are considered to be acidic amino acids, but will generally be found in their deprotonated, negatively charged state due to their carboxyl groups. They can form nice ionic interactions with metal ions. Finally, we have the basic amino acids which include arginine, lysine, and histidine. All of their side chains are nitrogen-containing.

​The CARS section of the MCAT for many is the most daunting one of all, despite being the only section on the exam that does not require any formal knowledge or content. This may be due to a test taker’s bad experience with the critical reading/verbal section of the SAT/ACT in the past, not being a native English speaker, or being a Canadian medical school applicant where the CARS section is more heavily weighted than the rest. Nevertheless, solid performance on CARS will demonstrate that you are academically well-rounded and have the ability to engage in rhetorical reasoning.
 
It is important to enter the CARS section with a tabula rasa (blank slate) to avoid allowing your internal biases and preconceptions influence your ability to choose the correct answer. If you ever find yourself choosing an answer choice in part because you personally agree with it, rather than having hard evidence from the passage to back it up, you are probably making a mistake. Instead, you should make it your job to determine what the author’s agenda is. Just like you do when you watch a newscast or read an article online, ask yourself, “What is the author trying to achieve by writing this.” This will help you determine what the main idea of the passage is – a central piece to performing well on the CARS section.
 
Try to engage in an argument with the author and the passage. Play the devil’s advocate. Look for logical flaws in the author’s argument and see if he/she supports all of the claims that are made with evidence or examples. This will keep you focused and engaged throughout the entire section – an issue some people tend to have especially when it comes to passages on philosophy and art.
 
After reading each paragraph, ask yourself why the author included it. What was the purpose of that sentence or phrase? Does it improve his/her argument? Try to quickly summarize each paragraph in your head as you move on. This will allow you to keep track of the overall argument and determine whether the author is maintaining the same viewpoint or is evolving it into a newer, more nuanced one. Realize that the authors of the passages will rarely (if ever) have an extreme viewpoint that resides on one part of a spectrum – this would leave them open to easy attacks. Rather, most passages take a middle-of-the-road approach, where the author will take some moderate stance, acknowledge the opposing arguments, and attempt to refute them.
 
As a cardinal rule, never choose an answer choice that contradicts the main idea in any way (unless of course the question expressly asks you to do so). Furthermore, if you are ever stuck between two answer choices (which happens fairly often) pick the one you think the author (not you!) would agree with the most. If you are having trouble formulating the complete main idea, look at what is going on towards the end of the passage. Usually, the author’s true agenda comes out then.
 
Above all, remain cool and confident. Try to have fun! 

To see it in practice, watch some of our videos below on approaching an AAMC CARS passage and questions.

Many of my students have come to me from other prep companies, lamenting that they were perfectly able to learn the content and recite the equations and concepts behind them, but were still performing poorly on practice exams. Even more, they often complain that they had never experienced this issue in undergrad. One of the main contributors to this problem is the MCAT's penchant for including highly technical and novel scientific passages that serve to disorient the test taker upon first glance. Many of these passages start by naming a slew of genes, proteins, and bioactive chemicals linked together in some pathway. Others will include a bunch of complicated figures and data presented in ways you may have never seen before. Here I will illustrate three methods I use to attack these kinds of passages:

1. Slow down and collect yourself - maintaining sharp focus and motivation is key to understanding the passage.
2. Read each word of the passage slowly and carefully. You should be constantly attempting to link any ideas you read about back to content you have already studied.
3. Although you should be paying close attention to the details, don't get too bogged down by them. Look for the main idea and ask yourself, "What is the point of this? What knowledge does the MCAT want me to demonstrate?" 

Additionally, when you are reading a passage that describes protein-protein interactions or mechanical contraptions in physics, you should be visualizing the process in your head the whole time and attempting to piece it all together. When encountering biochemical pathways, it may helpful for you to quickly jot down the order of the molecules and then refer to them when you get to the questions.  It is imperative that you have a solid understanding of most of the passage before you get to the questions - neither I nor any of my tutors condone skipping to the questions first or ignoring the passage altogether as many of the answers must be found from the passage.

Finally, when you get to the figures, begin by reading the caption and title (if available) and looking at the axes labels if there is a graph. This will give you an idea of what the data is supposed to show. On graphs, look for trends within the data points - is there an increase or decrease across the points or does it remain constant? Does this make sense in light of the passage? Feel free to refer back to the sentence or paragraph that cites the figure in question. For bar charts or box plots, you should be looking for comparisons. Is one drug more effective than the other (or do the error bars cross and no mention of a significant difference is made)?

Keep these ideas in mind as you read the passages. Remember to relax and as weird as it sounds, have fun! As a future physician, you will be expected to continue reading and evaluating research papers, drug trial outcomes, etc. and pass on that knowledge to your patients in hopes of improving their mental and physical health.

To get a feel for how I approach these passages, watch some of our videos on AAMC biology and chemistry passages below.

1. The MCAT is nothing like your undergrad physics classes.
In my physics classes in undergrad, we would get problems that would each take 15-20 minutes to solve. They were complicated, required knowledge of a pretty large and specific set of equations, and a fair amount of algebra/calculus in order to solve. Believe me when I tell you that the MCAT is nothing like that. For the most part, physics problems on the MCAT can be solved in a few steps, often relying on one core concept and 1-2 simple equations. The MCAT is more concerned with you being able to identify relationships between terms in an equation and will usually not expect you to actually perform extended computations for any given question.

2. Focus on broad concepts and relevant applications. Don't get bogged down by nitty gritty details.
A lot of prep books (Kaplan especially) liked to throw in equations and problems that are not at all necessary to know going into the exam. The MCAT wants to make sure you understand concepts outlined in the content list, not every single law/rule in your Giancoli physics textbook. For example, Kaplan spent a lot of time going over Kirchhoff's rules for solving complicated circuits despite it not being mentioned on the official content list. By doing so, they make it easy for you to overlook bigger and more important concepts that are much more likely to be tested and instead teach you rote/procedural problem solving that is much more relevant for a university course. Instead of knowing Kirchhoff's equations, know conceptually that the current through resistors in series is constant (conservation of charge, which is mentioned on the list) and that voltage across resistors in parallel is the same (conservation of energy). 

3. Each time you learn a new equation, practice seeing how messing with one of the variables would affect the others. 
The MCAT loves problems that ask you what happens to one variable when another variable changes. Recognize these relationships when you learn a new equation because it will reveal fundamental concepts. For example, for the Power equation for lens strength (P = 1/f, where f is the focal length of the lens in meters), it is evident that an increase in focal length decreases the refractive (bending power of a lens). Now you should ask yourself, what does a lens with a large focal length even look like? Does a it have a big curve or is it flat? Remember that the focal length is determined by creating an imaginary circle using the boundary of the lens, finding the radius of that circle, and dividing it by two. Now its evident that big focal length = flat lens. Why is any of this important? People with presbyopia (i.e. old people) have lenses that have crystallized and now have trouble bending. This means that their lenses have a big focal length...low refractive power...can't bend light well...image will converge too late (i.e. behind retina). How do we treat them? With converging (convex) lenses! Now we have made a full circle and have thrown in biological/medical applications. This is how the MCAT wants you to think.

4. Learn your units. 
The MCAT will once in a while throw in a problem where you will be like ??? but is actually extremely simple to solve using dimensional analysis. For instance, Power (this time the rate of energy transfer) is measured in Watts. Watts is composed of a J/s (remember, work/time). A Joule is composed of a kg*m^2/s^2. Know how to break down everything into basic SI units.

5. Rely less on your intuition, more on empirical data/equations.
Throughout my experience as an MCAT tutor, I have seen a lot of my students make the mistake of relying too much on raw intuition in order to solve physics problems. Keep in mind that your intuition can betray you, especially when you are outside of the mechanics realm (and into electricity, magnetism, quantum, etc.) For instance, does the magnetic force (F = qv x B = qvBsin(theta)) do any work on a moving charge? Intuitively, it may seem like the answer is yes, but if you do the math you'll see it is no! Because the lorentz force is a cross product, by definition it must be perpendicular to the velocity of the charge. When a force is perpendicular to an objects displacement, no work is done (W = Fdcos(theta)).

Watch some of these methods in action in our videos on AAMC MCAT physics passages.