MP 29 : MCAT Biology Passage Deep Dive

Session 29

This week, we're going to do a deep dive into a full biology MCAT passage as we show you how you can prevent yourself from falling into the trap of some “tricky” questions and ultimately beat the MCAT.

[01:34] Beta Oxidation Passage

This passage shows the description of the process of beta oxidation, how the body in the mitochondrion metabolizes fat for energy. It also shows a couple of different molecular structures of carnitine and palmitic acid as well as the first three steps of beta oxidation.

With the addition of biochemistry to the MCAT, the test raters are going to expect you to be very comfortable with all these different metabolic pathways, not quite to the level that you would learn them in medical school but it still has to be the kind of language you're comfortable reading about.

[02:25] Answering “Least” Questions

Question #41: Injection of insulin into the bloodstream is least likely to result in which of the following:

  • (A) Increased glycogen synthesis
  • (B) Decreased lipid synthesis
  • (C) Increased deesterification of fatty acids
  • (D) Decreased gluconeogenesis

(We know that insulin is a very powerful metabolic hormone so this is not directly coming from the passage itself but just related to the topic of the passage.)

[03:19] Bryan's Insights:

The question sounds like it's going to require a whole lot of hyper-detailed knowledge of the various metabolic results of insulin. When organizing all the various complicated biochemistry pathways, start with the broadest, most general understanding.

Insulin is arguably the most powerful anabolic hormone in the body that involves building up and storing big molecules. Knowing that it's big job is to store energy to build up big molecules, you can usually hack your way through this question and find your way to the right answer.

Choice (A) increased glycogen synthesis sounds like something insulin would do since it means more storage. However, a common mistake among students is they'd just pick this answer and move on, forgetting the word “least” in the question. Therefore, choice (A) is already crossed off.

Choice (B) decreased lipid synthesis is the right answer since insulin's job is to help us store energy. Since this is a “least” question, answer choice (B) is then the right answer.

[05:08] Tips to Prevent Mistakes in  Answering “Least” Questions

First, AAMC has written this where they've put all in caps, or italics, words like least, not, except, etc.

Second, the MCAT comes with a highlighting function where you can mouse over and highlight words in the passage or in the question. So if you see words like challenge, weaken, not, accept, or least, highlight it in the question itself. This visual reminder will help prevent any mistakes.

[06:07] Answering Roman Numeral Questions

Question #42: Which steps in Figure 3 are oxidations?

(Steps are presented in Roman Numerals. Figure 3 starts with a big long fatty acid tail attached to Coenzyme A.)

  1. Step 1 shows a single bond becoming a double bond.
  2. Step 2 shows the double bond going away and an OH (hydroxyl group) has now been tagged on where that double bond was.

III. Step 3 shows the OH group becomes a carbonyl carbon (C=O).

[07:11] Bryan's Insights:

There are different ways to answer Roman Numeral questions but do the easiest one first. In this case, going from a hydroxyl group (OH) to a carbonyl carbon (C=O) is fairly obviously an oxidation. It's a classic definition of oxidation set up when there are more bonds. So Step 3 is an oxidation. Let's just eliminate answer choice (A) and if this is far as you can get and you're not really sure about the other steps,t hat's fine. Take whatever progress you can get and make your best guess and move on.

Step 1 of the process going from a single bond to a double bond is another example of an oxidation step. So when we reduce or saturate a molecule, we reduce all the double bonds down to single bonds. And if you go the other way, going from a single bond to a double bond would be an oxidation step. So (I) is also an oxidation step.

Hence, Steps 1 and 3 are oxidations. This then leads us to eliminate another answer choice, (B), aside from (A) which we've already eliminated.

For the two remaining answer choices (C) and (D), we just have to decide whether Step 2 is an oxidation step. And this is a tricky question because a majority of students get this question wrong and think that Step 2 is an oxidation step so they pick the incorrect answer (D) whereas the right answer is (C)  I and III.

So you have to look back at Step 2 and figure out why it's not an oxidation. It's tricky in that the molecule starts from a double bond to adding a hydroxyl group. Students simply see the oxygen and they immediately conclude it's oxidation, without recognizing that since the double bond went away, that means one of the carbons got the OH group therefore the other carbon had to have gotten a hydrogen. The double bond did not just disappear so you had to put a hydrogen on there. Hence, this is not an oxidation step but a hydration step. They actually added water across a double bond.sure one carbon got an oxygen but the other carbon got a hydrogen.

This is tricky because you really have to think about what happened to the other carbon in that double bond. But ultimately, it's not a trick question because the figure is right there on your screen or handout.

[10:50] Final Thoughts

You just want to walk into the test being super comfortable with beta oxidation as a metabolic pathway so none of these steps will be something new. It's good to really know your metabolic pathways so you won't be worried about interpreting the figure correctly because it would be very comfortable for you already and you can instead just focus on the exact question asked.

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Transcript

Introduction

Dr. Ryan Gray: Have you checked out our Specialty Stories podcast yet over at www.SpecialtyStories.com? In that podcast we focus on medical specialties. As you're preparing for the MCAT, maybe you don't care what type of physician you want to be yet, you just want to get into medical school. But listening to the Specialty Stories will help keep you motivated as you're struggling through your MCAT prep. Hearing from different specialists and different physicians will help keep you motivated and encouraged, and I think will help your MCAT score. Go check out Specialty Stories at www.SpecialtyStories.com.

This is The MCAT Podcast, session number 29.

A collaboration between the Medical School Headquarters and Next Step Test Prep, The MCAT Podcast is here to make sure you have the information you need to succeed on your MCAT test day. We all know that the MCAT is one of the biggest hurdles as a premed, and this podcast will give you the motivation and information you need to know to help get you the score you deserve so you can one day call yourself a physician.

I'm excited to be here for another week of The MCAT Podcast and I appreciate you taking the time to listen. We're going to jump in to another episode here with Bryan.

Bryan, last week we had a set of biology discrete questions, this week we're going to do a deep dive into a full passage, so let's go ahead and talk about this one.

Question #1

Bryan Schnedeker: Sure absolutely. Sure as we always do with these podcasts, if the listener is able to get the handout, you can go ahead and pause the podcast for just a second and read your way through the passage carefully, and then we're going to talk about a couple of sample questions that come right along with it. What we see in the passage here is just a description of the process of beta-oxidation, how the body and the mitochondria metabolize fat for energy, with a couple of different molecular structures, they give us the structure of carnitine and palmitic acid, and then they give us the first three steps of beta-oxidation. With the addition of biochemistry to the MCAT, the test writers are going to expect you to be very comfortable, very familiar with all these different metabolic pathways. Maybe not quite to the level that you would obviously learn them in medical school, but this still has to be language that you're comfortable reading about. But then typical for the MCAT of course, they're going to introduce a general topic in a passage, or an experiment in the passage, and then the questions are just going to be scattershot around that topic. So the first question we have here number 41 says, ‘Injection of insulin into the bloodstream is least likely to result in which of the following?' So we know that insulin is a very powerful metabolic hormone, so this is not coming directly from the passage itself but it's just related to the topic of the passage. So again injection of insulin into the bloodstream is least likely to result in which of the following? And the choices are A, increased glycogen synthesis. B, decreased lipid synthesis. C, increased esterification of fatty acids. Or D, decreased gluconeogenesis. At first the question sounds like it's going to require a whole lot of hyper detailed knowledge about the various metabolic results of insulin. When I'm working with my own students to try and help them organize all the various complicated biochemistry pathways, I always say start with the broadest, most general understanding, right? Insulin is a powerful, arguably the most powerful anabolic hormone in the body. It's about building up and storing big molecules, not about making little molecules. So if you remember that insulin's big job is to store energy to build up big molecules, then you can usually hack your way through these questions and find your way to the right answer. So in this case answer choice A said increased glycogen synthesis, and that certainly sounds like something insulin would do, right? Glycogen, a storage polymer of glucose molecules, so increased glycogen synthesis, sure that means more storage. So that's something insulin would do. Now the mistake is of course a lot of students at that point would just go, ‘Oh A is the right answer,' pick it, and move on. But they forget that the word that I read twice now in the question itself was the word ‘least.' The question was injection of insulin into the bloodstream is least likely to result in which of the following? So A, increased glycogen synthesis, is a function of insulin and so we cross it off. Then we get to B, decreased lipid synthesis. And that's our winner, that's the right answer because insulin's job is to help us store energy, and B says decreased lipid synthesis. So as this is a least question, answer choice B then becomes the right answer.

Tips for Avoiding Mistakes

Dr. Ryan Gray: Do you have any sort of tips for when a student reads this passage, and you mentioned that they forget that ‘least' function there. What sort of tips do you have so that when they read that and they're looking over their answers, they're reminded that it's a ‘least' and kind of an opposite thing?

Bryan Schnedeker: Sure, yeah there are two big things there. First, one provided by the AAMC which is nice of them, they put it all in caps. So when they put words like ‘least,' ‘not,' ‘except,' they're going to put that in caps or italics or something. And then second, the MCAT comes with a highlighting function. You can mouse over words in the passage or even in the question, you can highlight words in the question. And so I tell my own students when you see a word like ‘challenge,' or ‘weaken,' or ‘not,' or ‘except,' or ‘least,' highlight it in the question itself. That little visual reminder will help prevent any mistakes like you're talking about.

Dr. Ryan Gray: Alrighty.

Question #2

Bryan Schnedeker: Okay let's look at one more from this passage. So question number 42 asks, ‘Which steps in figure three are oxidations?' And then the Roman numerals are just step one, step two, step three. And I'm going to describe what we see in the figure and of course if you're following along and printed the handout out, you can just see this directly. So figure three starts with a fatty acid, so a big long fatty acid tail attached to coenzyme A. Step one shows a single bond becoming a double bond. Step two shows the double bond going away, and then OH or hydroxyl group has now been tagged on where that double bond was. And then in step three that hydroxyl group, that OH group becomes a carbonyl carbon, C double bond to O. So those are your three steps. Single bond into a double bond, a double bond going away and now showing a hydroxyl group, OH group, and then finally a hydroxyl group OH becoming a C double bond to O. And once again the question is, ‘Which of these steps are oxidations?' And so when you have Roman numerals, there's different ways to tackle Roman numeral questions, but I always say do the easiest one first. So in this case going from a hydroxyl group, OH, to a carbonyl carbon, C double bond to O, it's fairly obviously an oxidation. It's more bonds to oxygen, kind of your classic definition of an oxidation set-up. So Roman numeral three, step three is an oxidation, and that lets us eliminate answer choice A. And if that's as far as you can get, if you're not really sure about the other steps, then that's fine. You've made some progress and you should take what progress you can get and make your best guess and move on. Next step one of the process, going from a single bond to a double bond, is another example of an oxidation step. So when we reduce or saturate a molecule, we reduce all the double bonds down to single bonds. So going the other way, going from a single bond to a double bond would be an oxidation step. So Roman number one is also an oxidation. Step one is an oxidation and step three is an oxidation. That lets us eliminate another answer choice. We've eliminated choice A, now we can eliminate choice B, and the two remaining answer choices C and D, we just have to decide whether or not step two is an oxidation step. And Ryan, here's where the tricky bit comes in for most students. When we actually look at how Next Step students have done on this test, and which answer choices, and which percentages students have picked, a majority of students get this question wrong. They think that step two is an oxidation step, and so they pick the incorrect answer, they pick D whereas the right answer is choice C, just only Roman one and three. And so we have to look back at step two and see why is it not an oxidation? Why is it tricky? It's tricky because the molecule starts with a double bond- remember the process was single bond, to double bond, to adding a hydroxyl group, to going to a carbonyl carbon. So the step going from a double bond to adding a hydroxyl group, my guess is that students simply see the oxygen and go, ‘Oh that's oxidation,' boom, done, and they don't even think about it. Without recognizing that now that the double bond went away, that means one of the carbons got the OH group, that means the other carbon had to have gotten a hydrogen, right? Because the double bond didn't just disappear, it doesn't become a radical, or a carbocation or something. So you had to put a hydrogen on there, but of course we don't just draw that, right? We don't draw the hydrogens when we're doing the little stick diagrams in orgo. So this isn't an oxidation step, it's a hydration step. They added water across a double bond. Sure one carbon got an oxygen but the other carbon got a hydrogen, and the way we think about redox in orgo is bonds to oxygen are oxidation, bonds to hydrogen are reduction. So you can't say the overall molecule got oxidized or reduced, they just added water across the double bond. So you've got to- it's a tricky question in the sense that you've got to really think about what happened to that other carbon in the double bond. But ultimately it's not a trick question, the figure is right there on the screen, or it's right there in your handout.

Dr. Ryan Gray: Okay, interesting. Yeah I- again having forgotten all of this, I see the O, the oxygen there and I'm like, ‘Oh yeah that's an oxidation.' So yeah exactly the trap that students fall into, or that you're assuming they fall into is definitely the trap that I fell into.

Bryan Schnedeker: Yeah absolutely. And I'll tell you the real trick here, the real takeaway point for our prep is we just want to walk into the test being super comfortable with beta-oxidation as a metabolic pathway, so none of these steps will be something new. I think the real trick is for students who maybe- they're not as good on their content so when question 42 comes up they suddenly start freaking out and analyzing the figure because it's new to them. Whereas if you really knew your metabolic pathways, you wouldn't be worried about interpreting the figure correctly because it would be really comfortable for you already, and you could instead just be focusing on exactly what the question asked.

Final Thoughts

Dr. Ryan Gray: Alright there you have it, another MCAT Podcast in the books. If you are on an iOS device and you do not subscribe to this podcast through a podcast app like The Podcasts, the official Apple podcast app, you should and you can do that very easily by opening up that podcast app. If you don't find it on your phone, search for it in the app store, it's hidden there. If you removed it, it's still there. Open it up, search for Med Ed Media, that's Med Ed Media with a space in there, and all four of the podcasts that we do at the Medical School Headquarters, you will find and you click subscribe and every week this podcast will come to you. Do me a favor while you're in there, you can leave a rating and review as well.

I hope you have a great week, but before I let you go, I want to remind you that Next Step Test Prep is known for their one-on-one tutoring, but did you know that they have a huge set of MCAT prep books, and ten full length MCAT practice exams that you can buy separately. So go check them out, that's www.NextStepTestPrep.com and use the promo code MCATPOD, that's MCATPOD, save some money on those practice exams, and save some money on their tutoring, and their awesome new course as well. Again that's MCATPOD, all capital letters for that coupon code.

Have a great week, we'll see you next week here at The MCAT Podcast.

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