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MCAT Amino Acids: What to Know

You have probably already heard that the new MCAT has a lot more biochemistry than the old MCAT. It’s not that there was no biochemistry on the old exam but it just wasn’t a major emphasis. On the new MCAT, biochemistry is the second most tested natural science subject after biology. You might now recall the pain of having to memorize the entire cellular respiration pathway and the structures of all the amino acids for your biochemistry class. It’s true these concepts will be tested on the MCAT but not to as much depth. In this post, we will talk about MCAT amino acids and what you need to know about them for the exam. If you want to learn more about how the MCAT has changed, check out our previous posts on New MCAT vs. Old MCAT and Is the New MCAT Harder than the Old MCAT.

What You Need to Know for the MCAT

If you talk to any student that has taken the new MCAT, they will tell you that amino acids are a big deal. You need to have all twenty amino acids memorized. This includes the structure of the side chains, the pKa of the side chain (if applicable), the one-letter code, and the three-letter code for each amino acid. In addition, you will need to be able to classify each as hydrophobic, hydrophilic, acidic, or basic. Below, we have an example of what you need to know for the acidic amino acid, glutamic acid:

MCAT Amino Acids

This is a lot to memorize but, unfortunately, there is more. According to the content outlines for the MCAT, you will also need to know:

  • How to synthesize amino acids, specifically the Strecker Synthesis and Gabriel Synthesis
  • Common amino acid reactions, including the formation of disulfide and peptide bonds
  • How to calculate the charge of an amino acid and its isoelectric point

We hope you get the point. MCAT amino acids are important. There are numerous ways that the exam can test these special organic compounds.
 
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MCAT Amino Acids Practice Questions

To give you an idea of how the MCAT tests amino acids, we have a couple practice questions for you to try. If you think you know the answers, go ahead and let us know by commenting below!

1. What is the net charge of the oligonucleotide DVLNQEK at pH 7?

A. +1

B. 0

C. -1

D. -2

2. Octopine is an analog of lactic acid found in the muscle tissue of some invertebrates. Which two amino acids is the compound (shown below) derived from?

MCAT Amino Acids 2

A. Gly and Arg

B. Ala and Lys

C. Ser and Tyr

D. Arg and Ala

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8 Responses to MCAT Amino Acids: What to Know

  1. Tas August 13, 2016 at 9:00 pm #

    Is the answer to #2 D?

    • Ken
      Ken August 14, 2016 at 5:36 pm #

      Hi Tas,

      Great job! Yes, the answer is D. 🙂

      Best,
      Ken

  2. Lauren August 17, 2016 at 7:34 am #

    Is #1 B?

    • Ken
      Ken August 17, 2016 at 7:41 am #

      Hi Lauren,

      You’re close but not quite right! Here are the steps you can take to answer these sort of questions:

      1. Determine which amino acids have acidic or basic side chains.
      2. Determine whether these side chains will be protonated or deprotonated by comparing their pKa values with the pH (don’t forget to take into account the N-terminus and C-terminus!)
      3. Add up the overall charges

      Hope that helps!

      Best,
      Ken

      • Kelsi August 17, 2016 at 10:05 am #

        Hi Ken! I thought B would be correct because you only take D and K into account? D is negatively charged and K is positively charged, so wouldn’t they cancel out at pH 7 because the C terminus would be deprotonated and the NH would still be protonated? I guess I’m confused.

        • Ken
          Ken August 17, 2016 at 10:12 am #

          Hi Kelsi,

          You are extremely close! Your approach is absolutely correct but there is one more acidic amino acid besides D. Once you figure out which amino acid I’m talking about, I’m sure you’ll figure it out!

          Best,
          Ken

          Best,
          Ken

  3. Gerry Mtike May 21, 2017 at 2:55 pm #

    Is #1 C and #2 D?

  4. Brianna August 4, 2017 at 9:06 pm #

    Thats right. #1 you count Lysine +, Glutamine -, and Aspartic acid -. And B is just memorization of amino acid structures


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