Re-Cap of Biology II

Hey everyone,

First and foremost, if you have not yet done Full-Length #1, that is your official homework for MSCT II!  Do NOT forget to complete this test!  WHEN YOU TAKE FULL-LENGTH #1, DO SO IN INTERNET EXPLORER!  THERE HAVE OCCASIONALLY BEEN GLITCHES REPORTED WITH SAFARI AND FIREFOX.  When you take Full-Length #1, don’t forget to turn off spell-check, grammar-check, and auto correct if you plan to complete the writing samples.

In regards to the question I got earlier tonight about bicarbonate and glycolysis, I have two things to consider (I'm not sure if either truly answers the question that was asked, but I'll give it a try):

-When the body is hypoxic (low oxygen) and must go into anaerobic respiration, it starts producing lactic acid.  This lactic acid, being an acid, meets up with the bicarbonate in the blood and causes a "metabolic acidosis" - that is, because of metabolic disturbances, the body becomes more acidic.  In particular, this is often refered to as a "high anion gap" acidosis, mainly because there are a lot of anions in solution that shouldn't be there (drinking a lot of HCl would be an example of a "low anion gap" acidosis).  Basically, lactic acid will lower blood bicarbonate levels.

-I found a few studies that indicate that increased bicarbonate stimulates glycolysis (most of these were done in bacterial models, but I'm guessing it also applies for humans -- our glycolytic enzymes are similar although not identical).  In particular, it seemed to activate one of the enzymes (glyceraldehye-3-phosphate dehydrogenase, or G3PDH), used right after glucose metabolites are split into two 3-carbon molecules.  I hope this helps!

This re-cap email is going to be a little different.  Since biology is, at its core, a visual science, I wanted to get a bunch of great online resources to you so you can see these processes occurring.  One of the most popular introductory biology textbooks, Life: The Science of Biology, has a companion website that has compiled an impressive array of animations that is available to the public (i.e. you don’t have to register with the website and/or provide proof of purchase to view the animations).  Given that we humans tend to learn better from visual stimuli, reviewing these animations may be a nice way to review the wealth of biology topics that might be tested on the MCAT.  Introductory biology courses cover a vast array of topics, far greater than what the MCAT covers, thus many of the animations on this website are not relevant to the biology you need to know for the MCAT.  Therefore, I have taken the time to specifically list the animations that are relevant to the MCAT below.  To help make your review more efficient, I’ve previewed each video and provided comments on the merits of each animation.  Enjoy!

List of animations from Life: The Science of Biology relevant to the MCAT

• Chapter 6, Tutorial 6.2: Allosteric Regulation of Enzymes
  • Some of the questions on AAMC exams like to play mind games with your ability to understand the difference between allosteric activators and inhibitors.  This topic can be combined with molecular biology and genetics concepts so it is in your interest to have a strong foundation in this concept so you can answer tough critical thinking questions related to enzymes.
• Chapter 7, Tutorial 7.1: Electron Transport and ATP Synthesis
  • Please note that you don’t need to know the names of the electron carriers… this animation is included in the list because while many students remember that oxygen is the final electron acceptor they tend to forget precisely how the generation of the proton gradient is the key player in actually leading to the synthesis of ATP.  This animation does a decent job of helping you visualize that process.
• Chapter 8, Tutorial 8.2: Photophosphorylation
  • What, photosynthesis?  Really?  Yes, really.  It’s on the AAMC list of topics and they have tested it in the past.  What you need to know is that during there are two phases: the light-reactions and the carbon-assimilation reactions (aka the dark reactions, but since that name is misleading it is being phased out).  This animation covers the light reactions, which explains how plants use sunlight to synthesize ATP and NADPH.  These products are used in the carbon-assimilation reactions to synthesize sugars.  Thus, at the end of the day we get the famous net reaction: CO₂ + H₂O + sunlight à O₂ + sugars.  As with ETC, you don’t need to know the details behind photophosphorylation…just the major concepts as I’ve discussed here.
• Chapter 9, Tutorial 9.1 and 9.2: Mitosis & Meiosis
  • These animations review what occurs in each stage of mitosis and meiosis.  In both animations, the parent cell has two pairs of chromosomes.
• Chapter 10, Tutorial 10.1 and 10.2: Independent Assortment of Alleles; Alleles that Do Not Assort Independently
  • The 9:3:3:1 phenotypic ratio that results from a dihybrid cross of two heterozygous parents is dependent upon this concept.  Most classical genetics questions presume that the alleles in question assort independently, but the AAMC has also tested your ability to answer questions about linked genes so make sure you’re up to speed on both scenarios.
• Chapter 11, Tutorial 11.1 and 11.3: DNA Replication, Part 1 and Part 2: Replication of a Chromosome and DNA Polymerization; Coordination of Leading and Lagging Strand Synthesis
  • These two animations review DNA replication quite thoroughly.  As usual, don’t memorize details…just re-familiarize yourself with the concepts.
• Chapter 12, Tutorial 12.1 and 12.3: Transcription and Translation
  • These animations cover the processes that lie at the heart of molecular biology.  It is in your interest to have a thorough understanding of these processes so that you can be prepared for some of the applications of these concepts to difficult passages and questions.
• Chapter 13, Tutorial 13.1 and 13.3: The lac and trp operon
  • These simple animations succinctly review the difference between inducible systems (lac operon) and repressible systems (trp operon).   
• Chapter 15, Tutorial 15.1: Signal Transduction
  • The content reviewed in this animation is NOT knowledge you need to know for Test Day, but it could be helpful for you to visualize how signal transduction cascade mechanisms proceed just in case you encounter a passage that discusses signal transduction.
• Chapter 18, Tutorial 18.1: Cells of the Immune System
  • There is no animation here – merely a detailed chart on the various cells of the immune system.  Most of the information presented in this chart is beyond the scope of what you need to know for the test, so it is not advised to memorize the information presented here; nevertheless, reviewing this chart briefly may help your comprehension of the organization of the immune system and how the various players interact with each other.  The key players to focus on are B cells, T cells, neutrophils, and macrophages. 
• Chapter 18, Tutorial 18.2: Pregnancy Test
  • This animation is way out of scope for the test.  It is suggested for review, because applications of immunology such as the one presented here is good fodder for an experimental style MCAT passage.  A well-organized animation like this one makes it easy to understand how the test works, but as you review this animation take note on how understanding this test may have been harder if it was presented to you on the MCAT in prose without any diagrams.
• Chapter 18, Tutorial 18.3 and 18.4: The Humoral Response and the Cellular Immune Response
  • These animations review the immune system in a bit more depth than the Kaplan Immunology Workshops, but while some of the content presented here is out of scope these animations should help clarify normal immune system function.  The word “normal” was underlined in the previous sentence because having a firm grasp on understanding how the immune system normally functions will help prepare you for questions that test your ability to apply that knowledge to explain and predict what occurs when things go wrong (such as in AIDS).
• Chapter 22, Tutorial 22.1: Natural Selection
  • There’s a few reasons I recommend this animation…one, it wouldn’t shock me if the MCAT asked you to be able to delineate the difference between directional, stabilizing or disruptive selection (in the context of a passage) and this animation does a really good job of explaining the difference.  Second, I find the bird throwing up after eating the unpalatable butterfly kind of cute. 
• Chapter 40, Tutorial 40.1: The Hypothalamus: The Body’s Thermostat
  • This animation nicely sums up the thermoregulatory function of the hypothalamus plus at the end we learn that the hypothalamus itself functions as a temperature sensor.
• Chapter 41, Tutorial 41.2: Hypothalamic-Pituitary-Endocrine Axis
  • A very nice review of the hypothalamus, and it even provides a nice chart summary of the major hormones and their functions.
• Chapter 41, Tutorial 41.3: Hormonal Regulation of Calcium
  • A very nice review of all the players (bone, kidney, digestive tract) that affect blood calcium levels.  Notice that homeostasis is still maintained even if the thyroid is removed. 
• Chapter 42, Tutorial 42.1: Fertilization
  • Almost all of this is out of scope, but it’s cool to see. 
• Chapter 42, Tutorial 42.2: The Ovarian and Uterine Cycles
  • These animations are quite fantastic, and all of the content reviewed is material you need to know for Test Day. 
• Chapter 43, Tutorial 43.1: Gastrulation
  • Embryology can be hard to understand without visual animations like this one…that said, embryology isn’t a high-yield topic so don’t get carried away with memorizing all of the content presented in this animation. 
• Chapter 44, Tutorial 44.1: The Resting Membrane Potential
  • This animation does a nice job of showing how the electrical and chemical gradients balance each other to create the negative resting membrane potential.  This topic seems innocent, but tough questions
• Chapter 44, Tutorial 44.2: The Action Potential
  • This animation teaches the action potential the exact same way the Kaplan MCAT Lesson Book does, so this animation is a nice review of material you have already covered in the classroom. 
• Chapter 44, Tutorial 44.3: Synaptic Transmission
  • A brief visual on what goes on at the pre-synaptic and post-synaptic membranes.
• Chapter 47, Tutorial 47.1: Molecular Mechanism of Muscle Contraction
  • A well-organized and thorough review of the entire mechanism of muscle contraction.  It has everything you need to know for Test Day.
• Chapter 48, Tutorial 48.2: Human Respiratory System
  • There’s nothing special here, as the Kaplan online workshop on the Respiratory System covers all the content in this animation.
• Chapter 49, Tutorial 49.1: The Cardiac Cycle
  • This animation is broken up into four “options”: the second and third options review material that is out-of-scope to the MCAT (still, it’s not hard to follow), but the first and fourth options are in-play.
• Chapter 50, Tutorial 50.1: The Digestion and Absorption of Fats
  • This animation nicely illustrates how bile emulsifies fats, and how that action facilitates their digestion.
• Chapter 50, Tutorial 50.2: Insulin and Glucagon Regulation
  • These animations review the effects of insulin and glucagon on the liver and blood glucose levels.
• Chapter 51, Tutorial 51.1: The Kidney
  • A concise and thorough review of almost everything you need to know about the kidney.  One major fault is that the animation fails to discuss the roles of ADH and aldosterone.

• Molecular Cell Biology Textbook, Chapter 3: SDS Gel Electrophoresis and Immunoblotting
  • These two animations hail from the same publishing company, but on a different website because they relate to their Molecular Cell Bio textbook.  These two animations provide an overview on how proteins are commonly studied in molecular biology labs.  Although some of the content and procedures discussed here are out of scope for the exam, the AAMC’s recent emphasis on molecular biology probably makes it worth your time to view these animations.  In fact, we recently received a report that one of the recent MCATs featured a challenging experimental passage about immunoblotting.

Reviewing all of these animations is a great way to get an overview of a large percentage of the biology you need to know for Test Day, but don’t get seduced into thinking that reviewing these animations will suffice.  Use the animations as one tool to help you prep for the MCAT.